Building Applications with Scala - Sergey Drozdov. Sausage ...sd.blackball.lv/library/Building_Applications_with_Scala_(2016).pdf · Building Applications with Scala Credits About

BuildingApplicationswithScala

TableofContents

BuildingApplicationswithScalaCreditsAbouttheAuthorAcknowledgmentsAbouttheReviewerwww.PacktPub.com

Whysubscribe?Preface

WhatthisbookcoversWhatyouneedforthisbookWhothisbookisforConventionsReaderfeedbackCustomersupport

DownloadingtheexamplecodeDownloadingthecolorimagesofthisbookErrataPiracyQuestions

1.IntroductiontoFP,Reactive,andScalaFunctionalprogrammingPrinciplesoffunctionalprogramming

ImmutabilityDisciplinedstatePurefunctionsandnosideeffectsFirst-classfunctionsandhigher-orderfunctionsTypesystemsReferentialtransparency

InstallingJava8andScala2.11ReadEvalPrintandLoop-REPLScalaHelloWorldusingtheREPL

ScalaREPLHelloWorldprogramScalaobject-orientedHelloWorldprogramScalaHelloWorldAppintheScalaREPLJavaHelloWorldapplication

Scalalanguage-thebasicsScalavariables-varandval

ScalaREPLvarusageScalavalusageattheScalaREPL

CreatingimmutablevariablesScalavariabletypeintheScalaREPL

ScalavariableswithexplicittypingattheScalaREPLScalaconditionalandloopsstatements

IfstatementsinScalaREPLIfstatementsinreturnstatementsinScalaREPLBasicforloopinScalaREPLForwithListinScalaREPLForwithifstatementsforfiltering-ScalaREPLJavacodeforfilteringevennumbers

ForcomprehensionsForcomprehensioninScalaREPLJavacodeforperformingfilteringwithcollections

ScalacollectionsCreating,removing,andgettinganitemfromamutablelistinScalaREPLScalatuplesScalaimmutableMapinScalaREPLScalamutableMapsatScalaREPL

MonadsScalaMapfunctioninScalaREPLOptionMonadinScalaAlistofallmethodsusingtheScalaREPL

Scalaclass,traits,andOOprogrammingAsimpleScalaclassinScalaREPLScalaplainoldJavaobjectinScalaREPLPersonclassinJava

TraitsandinheritanceScalainheritancecodeinScalaREPLScalatraitssamplecodeinScalaREPLScalatraitsusingvariablemixingtechniqueatScalaREPLScalatypealiassampleinScalaREPL

CaseclassesScalacaseclassesfeatureinScalaREPL

PatternMatcherSimplePatternMatcherinScalaAdvancedpatternmatcherinScalaREPLAdvancedcomplexpatternmatcherinScalaREPL

PartialfunctionsSimplePartialfunctioninScalaREPLScalaPartialFunctionwithoutOOusingcasestatementsinScalaREPLPartialFunctioncompositioninScalaREPL

Packageobjectspackage.scalaMainApp.scala

FunctionsPartialapplication

PartialfunctioninScalaREPLCurriedfunctions

Curriedfunctions-ScalaREPLCurriedtransformationinScalaREPL

OperatoroverloadingScalaoperatoroverloadinginScalaREPL

ImplicitsScalaImplicitsinSCALAREPLImplicitParameteratScalaREPL

FuturesSimpleFuturecodeinScalaREPLAcompleteFuturesampleatScalaREPL

ReactiveProgramingandRxScalaSimpleObservablesScalawithRxScalaSimpleObservablesScalawithRxScala-ExecutionintheconsoleComplexScalawithRxScalaObservables

Summary2.CreatingYourAppArchitectureandBootstrappingwithSBT

IntroducingSBTInstallingSBTonUbuntuLinuxGettingstartedwithSBTAddingdependenciesGeneratingEclipseprojectfilesfromSBTApplicationdistributionHelloworldSBT/ScalaAppBootstrappingourPlayframeworkappwithActivatorActivatorshellActivator-compiling,testing,andrunningSummary

3.DevelopingtheUIwithPlayFrameworkGettingstartedCreatingourmodelsCreatingroutesCreatingourcontrollersWorkingwithservicesConfiguringtheGuicemoduleWorkingwithviews(UI)Summary

4.DevelopingReactiveBackingServicesGettingstartedwithreactiveprogramming

IPriceService-ScalatraitPriceService-RxScalaPriceServiceimplementationGuiceInjection-Module.scalaNGServiceEndpoint

PlayframeworkandhighCPUusageRndDoubleGeneratorControllerIRndService.scala-ScalatraitRndService.scala-RndServiceimplementationModule.scala-GuiceInjectionsmain.scala.htmlproduct_details.scala.html

Summary5.TestingYourApplication

UnittestingprinciplesMakingcodetestableIsolationandself-containedtestsEffectivenamingLevelsoftesting

TestingwithJunitBehavior-DrivenDevelopment-BDDMyFirstPlaySpec.scala-FirstBDDwithScalaTestandthePlayframeworkTestingwithPlayframeworksupport

ProductService.scala-FIXthecodeissueImageServiceTestSpec.scala-ImageServiceTestReviewServiceTestSpec.scala-ReviewServicetest

TestingroutesRoutesTestingSpec.scala-Playframeworkroutetesting

ControllertestingRndDoubleGeneratorControllerTestSpec.scala-RndDoubleGeneratorControllertestsIntegrationSpec.scalaProductControllerTestSpec.scalaproduct_index.scala.htmlImageControllerTestSpec.scalaimage_index.scala.htmlReviewControllerTestSpec.scalareview_index.scala.htmlApplicationSpec.scalaNGServiceImplTestSpec.scalaNGServiceEndpointControllerTest.scala

Summary6.PersistencewithSlick

IntroducingtheSlickframeworkMySQLsetupConfiguringSlickinourPlayframeworkapp

ConfigurethedatabaseconnectionFPMMapping

ProductDaoReviewDAO

ImageDaoSlickevolutionsRefactoringservicesRefactoringcontrollersConfiguringDAOpackagesinGuiceRefactoringtestsGenericmocksServicetestsControllertestsRunningtheapplicationSummary

7.CreatingReportsIntroducingJasperReportsJasperReportsworkflowJaspersessionsInstallingJaspersoftStudio6ConfiguringMySQLDataAdapterinJaspersoftStudioCreatingaproductreportCreatingareviewreportCreatinganimagereportIntegratingJasperReportswithPlayframework

build.sbtGenericreportbuilderAddingthereporttotheproductcontrollerAddingthereporttothereviewcontrollerAddingthereporttotheimagecontroller

Routes-addingnewreportroutesNewcentralizedreportsUI

AddingthereportbuttonforeachviewSummary

8.DevelopingaChatwithAkkaAddingthenewUIintroductiontoAkkaIntroductiontotheActormodel

WhatisanActor?MessageexchangeandmailboxesCodingactorswithAkkaActorroutingPersistenceCreatingourchatapplicationThechatprotocolThechatcontroller

ImplementingthechatcontrollerConfiguringtheroutesWorkingontheUI

AddingAkkatestsScalatestforAkkaActorChatroomActortestChatBotAdminActortest

Summary9.DesignYourRESTAPI

IntroductiontoRESTRESTAPIdesign

HTTPverbsdesignUniformAPIResponsewithHTTPstatuscodesRESTAPIpatternsAPIversioningSomeanti-patternstobeavoided

CreatingourAPIwithRESTandJSONRestApiContoller

RESTAPIFrontControllerimplementationJSONmappingConfiguringnewroutesTestingtheAPIusingthebrowser

CreatingaScalaclientConfiguringplugins.sbtConfiguringbuild.sbtScalaclientcode

CreatingourRESTclientproxiesCreatingScalaTesttestsfortheproxiesAddingbackpressure

TheleakybucketalgorithmScalaleakybucketimplementationTestingbackpressure

AddingSwaggersupportSwaggerUI

BuildandinstallSwaggerStandaloneSummary

10.ScalingupStandalonedeployReportsfolderChangingreportbuilderDefiningthesecretRunningthestandalonedeployArchitectureprinciples

Serviceorientation(SOA/microservices)PerformanceScalability/Resiliency

ScalabilityprinciplesVerticalandhorizontalscaling(upandout)CachingLoadbalancerThrottlingDatabaseclusterCloudcomputing/containersAutoScalingAnoteaboutautomationDon'tforgetabouttelemetryReactiveDriversanddiscoverability

Mid-Tierloadbalancer,timeouts,Backpressure,andcachingScalingupmicroserviceswithanAkkaclusterScalinguptheinfrastructurewithDockerandAWScloudSummary

BuildingApplicationswithScala

BuildingApplicationswithScalaCopyright©2016PacktPublishing

Allrightsreserved.Nopartofthisbookmaybereproduced,storedinaretrievalsystem,ortransmittedinanyformorbyanymeans,withoutthepriorwrittenpermissionofthepublisher,exceptinthecaseofbriefquotationsembeddedincriticalarticlesorreviews.

Everyefforthasbeenmadeinthepreparationofthisbooktoensuretheaccuracyoftheinformationpresented.However,theinformationcontainedinthisbookissoldwithoutwarranty,eitherexpressorimplied.Neithertheauthor,norPacktPublishing,anditsdealersanddistributorswillbeheldliableforanydamagescausedorallegedtobecauseddirectlyorindirectlybythisbook.

PacktPublishinghasendeavoredtoprovidetrademarkinformationaboutallofthecompaniesandproductsmentionedinthisbookbytheappropriateuseofcapitals.However,PacktPublishingcannotguaranteetheaccuracyofthisinformation.

Firstpublished:December2016

Productionreference:1021216

PublishedbyPacktPublishingLtd.

LiveryPlace

35LiveryStreet

Birmingham

B32PB,UK.

ISBN978-1-78646-148-3

www.packtpub.com

http://www.packtpub.com

Credits

Author

DiegoPacheco

CopyEditor

SoniaMathur

Reviewer

YuanhangWang

ProjectCoordinator

SuzanneCoutinho

CommissioningEditor

KunalParikh

Proofreader

SafisEditing

AcquisitionEditor

DenimPinto

Indexer

TejalDaruwaleSoni

ContentDevelopmentEditor

RohitSingh

Graphics

JasonMonteiro

TechnicalEditor

JijoMaliyekal

ProductionCoordinator

MelwynDsa

AbouttheAuthorDiegoPachecoisanexperiencedsoftwarearchitectandDevOpspractitionerwithover10yearsofsolidexperience.HehasledarchitectureteamsusingopensourcesolutionssuchasJava,Scala,AmazonWebServices(AWS),Akka,ApacheCassandra,Redis,ActiveMQ,NetflixOSSStack-SimianArmy,RxJava,Karyon,Eureka,andRibbononcigcustomersinBrazil,London,Barcelona,India,andtheUSA.Diegohasapassionforfunctionalprogrammingandiscurrentlyworkingasasoftwarearchitect/agilecoachwithScala,Akka,andNetflixOSS.Duringhisfreetime,heenjoysgaming,blogging,andplayingwickedtunesonhisguitar.Youcancheckouthisblogathttp://diego-pacheco.blogspot.in/.

Someofhiscoreskillsincludethefollowing:

ArchitecturedesignandarchitecturecodingforhighscalablesystemsDistributedsystemsusingSOAandmicroservicesprinciples,tools,andtechniquesPerformancetuningandDevOpsengineeringFunctionalprogrammingandScalaAgilecoachingandservantleadershipforarchitectureteamsConsultancyondevelopmentpracticeswithXP/Kanban

Moreabouthimcanbefoundatthefollowing:

Linkedin:https://www.linkedin.com/in/diegopachecorsBlog:http://diego-pacheco.blogspot.in/Github:https://github.com/diegopachecoSlideshare:http://www.slideshare.net/diego.pacheco/presentationsPresentations:https://gist.github.com/diegopacheco/ad3e3804a5071ef219d1

HisrecentlecturesincludeNetflix(https://www.youtube.com/watch?v=Z4_rzsZd70o&feature=youtu.be),QCon(http://qconsp.com/sp2016/speaker/diego-pacheco),andAmazon(http://www.meetup.com/Sao-Paulo-Amazon-Web-Services-AWS-Meetup/events/229283010/).

http://diego-pacheco.blogspot.in/

https://www.linkedin.com/in/diegopachecors

http://diego-pacheco.blogspot.in/

https://github.com/diegopacheco

http://www.slideshare.net/diego.pacheco/presentations

https://gist.github.com/diegopacheco/ad3e3804a5071ef219d1

https://www.youtube.com/watch?v=Z4_rzsZd70o&feature=youtu.be

http://qconsp.com/sp2016/speaker/diego-pacheco

http://www.meetup.com/Sao-Paulo-Amazon-Web-Services-AWS-Meetup/events/229283010/

AcknowledgmentsFirstofall,I'mverythankfulforeverythingGodhasgiventomeinlife.So,IneedtosaythankyoutoGodatleastthreetimes.ThankyouGod,thankyouGod,thankyouGod.I’mverygladtohavefinishedthisbook,andIalsoneedtosayabigthankyoutoallmyfamilyandsupportivefriends,especiallyAndressaBicca,mytruelove;mymother,DeniseMaris;mygrandmother,Walkyria;andmydearfriends,MargaridaAvila,AdãoAvila,IsraelPrestes,andTaisdaRosa,foralltheirloveandsupport.IneedtosaythankstoPackt,especiallytoKirkD'costaandRohitKumarSinghforbeinggreateditors.Also,Ineedtosaythankyoutoilegra.comandespeciallytoIvãBoesingandRomuloDornellesforallthespace,trust,andsupport.Also,Icannotforgettosaythankyoutomycoworkers,customers,andfriends,whoaregreatpeopletoworkwith,andwhoI’velearnedalotfrom:SamSgro,DanielWildt,AnibalRojas,AlexandrePoletto,JefersonMachado,NilseuPadilha,JacksonSantos,ChristopheMarchal,JoelCorrea,andRafaelSouza.Finally,thankyoutoallofyouwhoboughtthisbookandhavereadit--youareawesome!

AbouttheReviewerYuanhangWangdescribeshimselfasanenthusiastofpurelyfunctionalprogrammingandneuralnetworks,withaprimaryfocusonDomainSpecificLanguage(DSL)design,andhehasdabbledinseveralfunctionalprogramminglanguages.HeiscurrentlyadatascientistatChinaMobileResearchCenter,workingonatypeddataprocessingengineandoptimizerbuiltontopofseveralbigdataplatforms.

www.PacktPub.comForsupportfilesanddownloadsrelatedtoyourbook,pleasevisitwww.PacktPub.com.

DidyouknowthatPacktofferseBookversionsofeverybookpublished,withPDFandePubfilesavailable?YoucanupgradetotheeBookversionatwww.PacktPub.comandasaprintbookcustomer,youareentitledtoadiscountontheeBookcopy.Getintouchwithusatservice@packtpub.comformoredetails.

Atwww.PacktPub.com,youcanalsoreadacollectionoffreetechnicalarticles,signupforarangeoffreenewslettersandreceiveexclusivediscountsandoffersonPacktbooksandeBooks.

https://www.packtpub.com/mapt

Getthemostin-demandsoftwareskillswithMapt.MaptgivesyoufullaccesstoallPacktbooksandvideocourses,aswellasindustry-leadingtoolstohelpyouplanyourpersonaldevelopmentandadvanceyourcareer.

http://www.PacktPub.com



https://www.packtpub.com/mapt

Whysubscribe?FullysearchableacrosseverybookpublishedbyPacktCopyandpaste,print,andbookmarkcontentOndemandandaccessibleviaawebbrowser

PrefaceFunctionalprogrammingstartedinacademiaandendedupintheITindustry.TheScalalanguageisamulti-paradigmlanguageusedbybigplayersandlargeorganizationsthathelpsyougetthecorrect(inthesenseofpurefunctionalprogramming)softwareand,atthesametime,softwarethatispracticalandscalable.

Scalahasaveryrichecosystem,includingPlayFramework,Akka,Slick,Gatling,Finable,andmore.Inthisbook,wewillstartrightfromthebasicprinciplesandideasonfunctionalandReactiveXprogramming,andthroughpracticalexamples,youwilllearnhowtocodewiththemostimportantframeworksoftheScalaecosystem,suchasPlay,Akka,andSlick.

YouwilllearnhowtobootstrapaScalaapplicationwithSBTandActivator,howtobuildaPlayandAkkaapplicationstepbystep,andwecoverthetheoryofhowtoscalemassiveScalaapplicationswithcloudandtheNetflixOSSstack.ThisbookwillhelpyoutogofromthebasicsubjectstothemostadvancedonesinordertomakeyouaScalaexpert.

WhatthisbookcoversChapter1,IntroductiontoFP,Reactive,andScala,looksathowtosetupaScaladevelopmentenvironment,thedifferencebetweenfunctionalprogrammingandobject-orientedprogramming,andtheconceptsoffunctionalprogramming.

Chapter2,CreatingYourAppArchitectureandBootstrappingwithSBT,discussestheoverallarchitecture,SBTbasics,andhowtocreateyourownapplication.

Chapter3,DevelopingtheUIwithPlayFramework,coverstheprinciplesofwebdevelopmentinScala,creatingourmodels,creatingourviews,andaddingvalidations.

Chapter4,DevelopingReactiveBackingServices,introducesyoutoreactiveprogrammingprinciples,refactoringourcontrollers,andaddingRxScalatoourservices.

Chapter5,TestingYourApplication,looksintotestingprincipleswithScalaandJUnit,behavior-drivendevelopmentprinciples,usingScalaTestspecsandDSLinourtests,andrunningourtestswithSBT.

Chapter6,PersistencewithSlick,coversprinciplesofdatabasepersistencewithSlick,workingwithFunctionalRelationalMappinginyourapplication,creatingthequeriesyouneedwithSQLsupport,andimprovingthecodewithasyncdatabaseoperations.

Chapter7,CreatingReports,helpsyouunderstandJasperreportsandadddatabasereportstoyourapplication.

Chapter8,DevelopingaChatwithAkka,discussestheactormodel,actorsystems,actorrouting,anddispatchers.

Chapter9,DesignYourRESTAPI,looksintoRESTandAPIdesign,creatingourAPIwithRESTandJSON,addingvalidations,addingbackpressure,andcreatingaScalaclient.

Chapter10,ScalingUp,touchesuponthearchitectureprinciplesandscalinguptheUI,reactivedrivers,anddiscoverability.Italsocoversmiddle-tierloadbalancers,timeouts,backpressure,andcaching,andguidesyouthroughscalingupmicroserviceswithanAkkaclusterandscalinguptheinfrastructurewithDockerandAWScloud.

WhatyouneedforthisbookForthisbook,youwillneedthefollowing:

UbuntuLinux14orsuperiorJava8update48orsuperiorScala2.11.7TypesafeActivator1.3.9JasperReportsDesignerWindowsfontsforLinuxEclipseIDE

WhothisbookisforThisbookisforprofessionalswhowantlearnScala,aswellasfunctionalandreactivetechniques.Thisbookismainlyfocusedonsoftwaredevelopers,engineers,andarchitects.Thisisapracticalbookwithpracticalcode;however,wealsohavetheoryaboutfunctionalandreactiveprogramming.

ConventionsInthisbook,youwillfindanumberoftextstylesthatdistinguishbetweendifferentkindsofinformation.Herearesomeexamplesofthesestylesandanexplanationoftheirmeaning.

Codewordsintext,databasetablenames,foldernames,filenames,fileextensions,pathnames,dummyURLs,userinput,andTwitterhandlesareshownasfollows:"ThenextstepistocreatetheenvironmentvariablecalledSCALA_HOME,andtoputtheScalabinariesinthePATHvariable."

Ablockofcodeissetasfollows:

packagescalabook.javacode.chap1;

publicclassHelloWorld{

publicstaticvoidmain(Stringargs[]){

System.out.println("HellowWorld");

}

}

Anycommand-lineinputoroutputiswrittenasfollows:

exportJAVA_HOME=~/jdk1.8.0_77

exportPATH=$PATH:$JAVA_HOME/bin

Newtermsandimportantwordsareshowninbold.Wordsthatyouseeonthescreen,forexample,inmenusordialogboxes,appearinthetextlikethis:"TheActorbehavioristhecodeyouwillhaveinsideyourActor."

Note

Warningsorimportantnotesappearinaboxlikethis.

Tip

Tipsandtricksappearlikethis.

ReaderfeedbackFeedbackfromourreadersisalwayswelcome.Letusknowwhatyouthinkaboutthisbook--whatyoulikedordisliked.Readerfeedbackisimportantforusasithelpsusdeveloptitlesthatyouwillreallygetthemostoutof.

Tosendusgeneralfeedback,[email protected],andmentionthebook'stitleinthesubjectofyourmessage.

Ifthereisatopicthatyouhaveexpertiseinandyouareinterestedineitherwritingorcontributingtoabook,seeourauthorguideatwww.packtpub.com/authors.

http://www.packtpub.com/authors

CustomersupportNowthatyouaretheproudownerofaPacktbook,wehaveanumberofthingstohelpyoutogetthemostfromyourpurchase.

DownloadingtheexamplecodeYoucandownloadtheexamplecodefilesforthisbookfromyouraccountathttp://www.packtpub.com.Ifyoupurchasedthisbookelsewhere,youcanvisithttp://www.packtpub.com/supportandregistertohavethefilese-maileddirectlytoyou.

Youcandownloadthecodefilesbyfollowingthesesteps:

1. Loginorregistertoourwebsiteusingyoure-mailaddressandpassword.2. HoverthemousepointerontheSUPPORTtabatthetop.3. ClickonCodeDownloads&Errata.4. EnterthenameofthebookintheSearchbox.5. Selectthebookforwhichyou'relookingtodownloadthecodefiles.6. Choosefromthedrop-downmenuwhereyoupurchasedthisbookfrom.7. ClickonCodeDownload.

Oncethefileisdownloaded,pleasemakesurethatyouunziporextractthefolderusingthelatestversionof:

WinRAR/7-ZipforWindowsZipeg/iZip/UnRarXforMac7-Zip/PeaZipforLinux

ThecodebundleforthebookisalsohostedonGitHubathttps://github.com/PacktPublishing/Building-Applications-with-Scala.Wealsohaveothercodebundlesfromourrichcatalogofbooksandvideosavailableathttps://github.com/PacktPublishing/.Checkthemout!

http://www.packtpub.com

http://www.packtpub.com/support

https://github.com/PacktPublishing/Building-Applications-with-Scala

https://github.com/PacktPublishing/

DownloadingthecolorimagesofthisbookWealsoprovideyouwithaPDFfilethathascolorimagesofthescreenshots/diagramsusedinthisbook.Thecolorimageswillhelpyoubetterunderstandthechangesintheoutput.Youcandownloadthisfilefromhttps://www.packtpub.com/sites/default/files/downloads/BuildingApplicationswithScala_ColorImages.pdf

https://www.packtpub.com/sites/default/files/downloads/BuildingApplicationswithScala_ColorImages.pdf

ErrataAlthoughwehavetakeneverycaretoensuretheaccuracyofourcontent,mistakesdohappen.Ifyoufindamistakeinoneofourbooks--maybeamistakeinthetextorthecode--wewouldbegratefulifyoucouldreportthistous.Bydoingso,youcansaveotherreadersfromfrustrationandhelpusimprovesubsequentversionsofthisbook.Ifyoufindanyerrata,pleasereportthembyvisitinghttp://www.packtpub.com/submit-errata,selectingyourbook,clickingontheErrataSubmissionFormlink,andenteringthedetailsofyourerrata.Onceyourerrataareverified,yoursubmissionwillbeacceptedandtheerratawillbeuploadedtoourwebsiteoraddedtoanylistofexistingerrataundertheErratasectionofthattitle.

Toviewthepreviouslysubmittederrata,gotohttps://www.packtpub.com/books/content/supportandenterthenameofthebookinthesearchfield.TherequiredinformationwillappearundertheErratasection.

http://www.packtpub.com/submit-errata

https://www.packtpub.com/books/content/support

PiracyPiracyofcopyrightedmaterialontheInternetisanongoingproblemacrossallmedia.AtPackt,wetaketheprotectionofourcopyrightandlicensesveryseriously.IfyoucomeacrossanyillegalcopiesofourworksinanyformontheInternet,pleaseprovideuswiththelocationaddressorwebsitenameimmediatelysothatwecanpursuearemedy.

Pleasecontactusatcopyright@packtpub.comwithalinktothesuspectedpiratedmaterial.

Weappreciateyourhelpinprotectingourauthorsandourabilitytobringyouvaluablecontent.

QuestionsIfyouhaveaproblemwithanyaspectofthisbook,[email protected],andwewilldoourbesttoaddresstheproblem.

Chapter1.IntroductiontoFP,Reactive,andScalaInourfirstchapter,wewilllearnthebasicconceptsofFunctionalPrograming(FP),reactiveprogramming,andtheScalalanguage.Theseconceptsarelistedasfollows:

SettingupaScaladevelopmentenvironmentwithEclipseScalaIDE.Basicconstructsofthelanguagelikevar,val,for,if,switch,andoperatoroverload.ThedifferencebetweenFPandobject-orientedprogramming.PrinciplesofpureFP:immutability,nosideeffects,statediscipline,composition,andhigherorderfunctions.ConceptsofFPsuchaslambda,recursion,forcomprehensions,partialfunctions,Monads,currying,andfunctions.PatternMatcher,recursion,reflection,packageobjects,andconcurrency.

Let'sgetgoing!

FunctionalprogrammingFPisnotnewatall.TheveryfirstimplementationofFPisLispandisdatedfromthe1950s.Currently,wearelivinginapost-functionalprogrammingera,wherewehavethestrongmathprinciplesandideasfromthe50smixedwiththemostmodernandbeautifulpieceofengineering,alsoknowastheJavaVirtualMachine(JVM).Scalaisapost-functionalprogramminglanguagebuiltontopoftheJVM.BeingontopoftheJVMgivesusalotofbenefitssuchasthefollowing:

Scalaisapost-functionalprogramminglanguagebuiltontopoftheJVM.BeingontopoftheJVMgivesusalotofbenefitssuchasthefollowing:

Reliabilityandperformance:Javaisusedby10outof10topwebsiteswehavecurrently,likeNetflix,Apple,Uber,Twitter,Yahoo,eBay,Yelp,LinkedIn,Google,Amazon,andmanyothers.JVMisthebestsolutionatscaleandisbattle-testedbytheseweb-scalecompanies.NativeJVMeco-system:FullaccesstoalloftheJavaecosystemincludingframeworks,libraries,servers,andtools.Operationsleverage:YouroperationteamcanrunScalainthesamewaytheyrunJava.Legacycodeleverage:ScalaallowsyoutoeasilyintegrateScalacodewithJavacode.ThisfeatureisgreatbecauseitenablesJavalegacysystemintegrationinsidethebox.Javainteroperability:AcodewritteninScalacanbeaccessedinJava.

Scalawascreatedin2001atEPFLbyMartinOdersky.Scalaisastrongstatic-typedlanguage,andwasinspiredbyanotherfunctionallanguagecalledHaskell.ScalaaddressesseveralcriticismsoftheJavalanguage,anddeliversabetterdeveloperexperiencethroughlesscodeandmoreconciseprograms,withoutlosingperformance.

ScalaandJavasharethesameinfrastructureastheJVM,butintermsofdesign,ScalaisadifferentlanguageincomparisonwithJava.Javaisanimperativeobject-orientedlanguageandScalaisapost-functional,multiparadigmprograminglanguage.FPworkswithdifferentprinciplesthanobject-orientedprograming(OOP).OOPgotverypopularandwellestablishedinenterprisethankstolanguageslikeJava,C#,Ruby,andPython.However,languageslikeScala,Clojure,F#,andSwiftaregainingahugemomentum,andFPhasgrownalotinthelast10years.Mostofthenewlanguagesarepurefunctional,post-functional,orhybrid(likeJava8).Inthisbook,youwillseeScalacodecomparedwithJavacodesoyoucanseebyyourselfhowScalaiswaymorecompact,objective,anddirectthanJavaandimperativeOOPlanguages.

FPstartedatacademiaandspreadtotheworld;FPiseverywhere.BigDataandStreamprocessingsolutionslikeHadoopandSpark(builtontopofScalaandAkka)arebuiltontopofFPideasandprinciples.FPspreadtoUIwithRxJavaScript-youcanevenfindFPinadatabasewithDatomic(Clojure).LanguageslikeClojureandScalamadeFPmorepracticalandattractivetoenterpriseandprofessionaldevelopers.Inthisbook,wewillbeexploring

bothprinciplesandpracticalaspectsoftheScalalanguage.

PrinciplesoffunctionalprogrammingFPisawayofthinking,aspecificstyleofconstructingandbuildingprograms.HavinganFPlanguagehelpsalotintermsofsyntax,butattheendoftheday,it'sallaboutideasanddevelopermindset.FPfavorsdisciplinedstatemanagementandimmutabilityinadeclarativeprogrammingwayratherthantheimperativeprogrammingmostlyusedbyOOPlanguagessuchasJava,Python,andRuby.

FPhasrootsinmathbacktoLambdacalculus-aformalsystemdevelopedinthe1930s.Lambdacalculusisamathematicalabstractionandnotaprogramminglanguage,butitiseasytoseeitsconceptsinprogramminglanguagesnowadays.

Imperativeprogrammingusesstatementstochangetheprogramstate.Inotherwords,thismeansyougivecommandstotheprogramtoperformactions.Thiswayofthinkingdescribesasequenceofstepsonhowtheprogramneedstooperate.WhatyouneedtokeepinmindisthekindofstylefocusonhowFPworksinadifferentway,focusingonwhattheprogramshouldaccomplishwithouttellingtheprogramhowtodoit.WhenyouarecodinginFP,youtendtousefewervariables,forloops,andIFS,andwritemorefunctionsandmakefunctioncomposition.

ThefollowingaretheCOREprinciplesofFP:

ImmutabilityDisciplinedstatePurefunctionsandnosideeffects/disciplinedstatesFirstclassfunctionsandhighorderfunctionsTypesystemsReferentialtransparency

Let'sunderstandtheseprinciplesindetail.

ImmutabilityTheconceptofimmutabilityistheCOREofFP,anditmeansthatonceyouassignavaluetosomething,thatvaluewon'tchange.Thisisveryimportant,becauseiteliminatessideeffects(anythingoutsideofthelocalfunctionscope),forinstance,changingothervariablesoutsidethefunction.Immutabilitymakesiteasiertoreadcode,becauseyouknowthefunctionthatyouareusingisapurefunction.Sinceyourfunctionhasadisciplinedstateanddoesnotchangeothervariablesoutsideofthefunction,youdon'tneedtolookatthecodeoutsidethefunctiondefinition.Thissoundslikeyou'renotworkingwithstateatall,sohowwoulditbepossibletowriteprofessionalapplicationsthisway?Well,youwillchangestatebutinaverydisciplinedway.Youwillcreateanotherinstanceoranotherpointertothatinstance,butyouwon'tchangethatvariable'svalue.Havingimmutabilityisthekeytohavingbetter,faster,andmorecorrectprograms,becauseyoudon'tneedtouselocksandyourcodeisparallelbynature.

DisciplinedstateSharedmutablestateisevil,becauseitismuchhardertoscaleandtorunitconcurrently.Whatissharedmutablestate?Asimplewaytoseeitisasaglobalvariablethatallyourfunctionshaveaccessto.Whyisthisbad?Firstofall,becauseitishardtokeepthisstatecorrectsincetherearemanyfunctionsthathavedirectaccesstothisstate.Second,ifyouareperformingrefactoring,thiskindofcodeisoftenthehardesttorefactoraswell.It'salsohardtoreadthiscode.Thisisbecauseyoucannevertrustthelocalmethod,sinceyourlocalmethodisjustonepartoftheprogram.Andwithmutablestate,youneedtolookupforallthefunctionsthatusethatvariable,inordertounderstandthelogic.It'shardtodebugfortheverysamereason.WhenyouarecodingwithFPprinciplesinmind,youavoid,asmuchaspossible,havingasharedmutablestate.Ofcourseyoucanhavestate,butyoushouldkeepitlocal,whichmeansinsideyourfunction.Thisisthestatediscipline:youusestate,butinaverydisciplinedway.Thisissimple,butitcouldbehardespeciallyifyouareaprofessionaldeveloper,becausethisaspectisnowusualtoseeinenterpriselanguagessuchasJava,.NET,Ruby,andPython.

PurefunctionsandnosideeffectsPurefunctionsaretheoneswithnosideeffects.Sideeffectsarebad,becausetheyareunpredictableandmakeyoursoftwarehardtotest.Let'ssayyouhaveamethodthatreceivesnoparametersandreturnsnothing--thisisoneoftheworstthingswecouldhave,becausehowdoyoutestit?Howcanyoureusethiscode?Thisisnotwhatwecallapurefunction.Whatarethepossiblesideeffects?Databasecall,globalvariables,IOcall,andsoon.Thismakessense,butyoucannothaveaprogramwithjustpurefunctions,becauseitwon'tbepractical.

First-classfunctionsandhigher-orderfunctionsFirst-classmeansthatthelanguagetreatsfunctionsasfirst-classcitizens.Inotherwords,itmeanshavinglanguagesupporttopassfunctionsasargumentstootherfunctionsandtoreturnvaluesasfunctions.First-classfunctionalsoimpliesthatthelanguageallowsyoutostorefunctionsasvariablesoranyotherdatastructure.

Higher-orderfunctionsarerelatedtoFirst-classfunctions,buttheyarenotthesamething.Higher-orderfunctionsoftenmeanslanguagesupportforpartialfunctionalapplicationandCurrying.Higher-orderfunctionsareamathematicalconceptwherefunctionsoperatewithotherfunctions.

Partialfunctionsarewhenyoucanfixavalue(argument)toaparticularfunction,whichyoumayormaynotchangelateron.Thisisgreatforfunctioncomposition.

Curryingisatechniquetotransformafunctionwithmultipleparametersinasequenceoffunctionswitheachfunctionhavingasingleargument.Scalalanguagedoesnotforcecurrying,however,languageslikeMLandHaskellalmostalwaysusethiskindoftechnique.

TypesystemsTypesystemisallaboutthecompiler.Theideaissimple:youcreateatypesystem,andbydoingso,youleveragethecompilertoavoidallkindsofmistakesanderrors.Thisisbecausethecompilerhelpsinmakingsurethatyouonlyhavetherighttypesasarguments,turnstatements,functioncomposition,andsoon.Thecompilerwillnotallowyoudomakeanybasicmistakes.ScalaandHaskellareexamplesoflanguagesthatareStrong-type.Meanwhile,CommonLisp,Scheme,andClojurearedynamiclanguagesthatmayacceptwrongvaluesduringcompilationtime.Oneofthebiggestbenefitsofthestrongtypesystemisthatyouhavetowritefewertests,becausethecompilerwilltakecareofseveralissuesforyou.Forinstance,ifyouhaveafunctionthatreceivesastring,itcouldbedangerous,becauseyoucanpassprettymuchanythinginastring.However,ifyouhaveafunctionthatreceivesatypecalledsalesman,thenyoudon'twriteavalidationtocheckifitisasalesman.Allthismaysoundsilly,butinarealapplication,thissaveslotsoflinesofcodeandmakesyouprogrambetter.Anothergreatbenefitofstrongtypingisthatyouhavebetterdocumentation,asyourcodebecomesyourdocumentation,andit'swaymoreclearwhatyoucanorcan'tdo.

ReferentialtransparencyReferentialtransparencyisaconceptwhichworksclosewithpurefunctionsandimmutabilitysinceyourprogramhasfewerassignmentstatements,andoftenwhenyouhaveit,youtendtoneverchangethatvalue.Thisisgreatbecauseyoueliminatesideeffectswiththistechnique.Duringprogramexecution,anyvariablecanbereplacedsincetherearenosideeffects,andtheprogrambecomesreferentiallytransparent.Scalalanguagemakesthisconceptveryclearthemomentyoudeclareavariable.

InstallingJava8andScala2.11ScalarequiresJVMtowork,soweneedgettheJDK8beforeinstallingScala.GototheOraclewebsite,anddownloadandinstallJDK8fromhttp://www.oracle.com/technetwork/pt/java/javase/downloads/index.html.

Onceyou'vedownloadedJava,weneedtoaddJavatothePATHvariable;otherwise,youcanusetheterminal.Wedothisasfollows:

$cd~/

$wget--no-cookies--no-check-certificate--header"Cookie:

gpw_e24=http%3A%2F%2Fwww.oracle.com%2F;oraclelicense=accept-securebackup-

cookie""

http://download.oracle.com/otn-pub/java/jdk/8u77-b03/jdk-8u77-linux-

i586.tar.gz"

$tar-xzvf$jdk-8u77-linux-x64.tar.gz

$rm-fjdk-8u77-linux-x64.tar.gz

ThenextstepistocreatetheenvironmentvariablecalledJAVA_HOME,andtoputtheJava8binariesinthePATHvariable.InLinux,weneedtoeditthe~/.bashrcfile,andexportthevariablesweneed,likeinthefollowing:

exportJAVA_HOME=~/jdk1.8.0_77

exportPATH=$PATH:$JAVA_HOME/bin

Savethefile,andthenonthesameterminalweneedtosourcethefilevia$source~/.bashrc

NowwecantestourJava8installation.Justtypein$java-version.Youshouldseesomethinglikethefollowing:

$java-version

javaversion"1.8.0_77"

Java(TM)SERuntimeEnvironment(build1.8.0_77-b03)

JavaHotSpot(TM)ServerVM(build25.77-b03,mixedmode)

Let'sgetstarted.WewillbeusingthelatestScalaversion2.11.8.However,thecodeinsidethisbookshouldworkwithanyScala2.11.xversion.Firstofall,let'sdownloadScalafromhttp://www.scala-lang.org/.

ScalaworksonWindows,Mac,andLinux.Forthisbook,IwillshowhowtouseScalaonUbuntuLinux(Debian-based).Openyourbrowserandgotohttp://www.scala-lang.org/download/.

Downloadscala2.11.8:itwillbeaTGZfile.Extractitandaddittoyourpath;otherwise,youcanusetheterminal.Dothisasfollows:

$cd~/

$wgethttp://downloads.lightbend.com/scala/2.11.8/scala-2.11.8.tgz

http://www.oracle.com/technetwork/pt/java/javase/downloads/index.html

http://www.scala-lang.org/

http://www.scala-lang.org/download/

$tar-xzvfscala-2.11.8.tgz

$rm-rfscala-2.11.8.tgz

ThenextstepistocreatetheenvironmentvariablecalledSCALA_HOME,andtoputtheScalabinariesinthePATHvariable.InLinux,weneedtoeditthe~/.bashrcfileandexportthevariablesweneed,likeinthefollowing:

exportSCALA_HOME=~/scala-2.11.8/

exportPATH=$PATH:$SCALA_HOME/bin

Savethefile,andthen,onthesameterminal,weneedtosourcethefilevia$source~/.bashrc.

NowwecantestourScalainstallation.Justtypein$scala-version.Youshouldseesomethinglikethefollowing:

$scala-version

Scalacoderunnerversion2.11.8--Copyright2002-2016,LAMP/EPFL

YouhavesuccessfullyinstalledJava8andScala2.11.NowwearereadytostartlearningtheFPprinciplesinScala.Forthis,wewillbeusingtheScalaREPLinthebeginning.ScalaREPLisbundledwiththedefaultScalainstallation,andyoujustneedtotype$scalainyourterminalasfollows:

$scala

WelcometoScala2.11.8(JavaHotSpot(TM)ServerVM,Java1.8.0_77).

Typeinexpressionsforevaluation.Ortry:help.

scala>

ScalaREPL

Congratulations!YouhaveinstalledJava8andScala2.11successfully.

ReadEvalPrintandLoop-REPLReadEvalPrintandLoop(REPL)isalsoknowasalanguageshell.Manyotherlanguageshaveshells,likeLisp,Python,andRubyforinstance.TheREPLisasimpleenvironmenttoexperimentthelanguagein.It'spossibletowriteverycomplexprogramsusingREPL,butthisisnottheREPLgoal.UsingREPLdoesnotinvalidatetheusageofanIDElikeEclipseorIntelliJIDEA.REPLisidealfortestingsimplecommandsandprogramswithouthavingtospendmuchtimeconfiguringprojectslikeyoudowithanIDE.TheScalaREPLallowsyoutocreateavariable,functions,classes,andcomplexfunctionsaswell.Thereisahistoryofeverycommandyouperform;thereissomelevelofautocompletetoo.AsaREPLuser,youcanprintvariablevaluesandcallfunctions.

ScalaHelloWorldusingtheREPLLet'sgetstarted.Goahead,openyourterminal,andtype$scalainordertoopentheScalaREPL.OncetheREPLisopen,youcanjusttype"HelloWorld".Bydoingthis,youperformtwooperations:evalandprint.TheScalaREPLwillcreateavariablecalledres0,andstoreyourStringthere.Thenitwillprintthecontentoftheres0variable.

ScalaREPLHelloWorldprogramWewillseehowtocreateHelloWorldprograminScalaREPLasfollows:

$scala

WelcometoScala2.11.8(JavaHotSpot(TM)64-BitServerVM,Java1.8.0_77).


scala>"HelloWorld"

res0:String=HelloWorld

scala>

Scalaisahybridlanguage,whichmeansitisobject-orientedandfunctionalaswell.YoucancreateclassesandobjectsinScala.NextwewillcreateacompleteHelloWorldapplicationusingclasses.

Scalaobject-orientedHelloWorldprogramWewillseehowtocreateobject-orientedHelloWorldprograminScalaREPLasfollows:

$scala



scala>objectHelloWorld{

|defmain(args:Array[String])=println("HelloWorld")

|}

definedobjectHelloWorld

scala>HelloWorld.main(null)

HelloWorld

scala>

Thefirstthingyouneedtorealizeisthatweusethewordobjectinsteadofclass.TheScalalanguagehasdifferentconstructscomparedtoJava.ObjectisasingletoninScala.It'sthesameascodingthesingletonpatterninJava.

NextweseetheworddefthatisusedinScalatocreatefunctions.Intheprecedingprogram,wecreatethemainfunctionsimilartothewaywedoitinJava,andwecallthebuilt-infunctionprintlninordertoprinttheStringHelloWorld.ScalaimportssomeJavaobjectsandpackagesbydefault.CodinginScaladoesnotrequireyoutotype,forinstance,System.out.println("HelloWorld"),butyoucanifyouwant.Let'stakealookatitinthefollowingcode:

$scala



scala>System.out.println("HelloWorld")

HelloWorld

scala>

Wecanandwewilldobetter.Scalahassomeabstractionsforaconsoleapplication,sowecanwritethiscodewithalessernumberoflinesofcode.Toaccomplishthisgoal,weneedtoextendtheScalaclassApp.WhenweextendfromApp,weperforminheritanceandwedon'tneedtodefinethemainfunction.Wecanjustputallthecodeinthebodyoftheclass,whichisveryconvenientandmakesthecodecleanandsimpletoread.

ScalaHelloWorldAppintheScalaREPLWewillseehowtocreateScalaHelloWorldAppinScalaREPLasfollows:

$scala



scala>objectHelloWorldextendsApp{

|println("HelloWorld")

|}

definedobjectHelloWorld

scala>HelloWorld

objectHelloWorld

scala>HelloWorld.main(null)

HelloWorld

scala>

AftercodingtheHelloWorldobjectintheScalaREPLwecanasktheREPLwhatHelloWorldis,andasyoumightrealize,theREPLwillanswerthatHelloWorldisanobject.ThisisaveryconvenientScalawaytocodeconsoleapplications,becausewecanhaveaHelloWorldapplicationwithjustthreelinesofcode.Sadly,tohavethesameprograminJava,itrequiredwaymorecode.Javaisagreatlanguageforperformance,butitisaverboselanguagecomparedwithScala,forinstance.

JavaHelloWorldapplicationWewillseehowtocreateJavaHelloWorldapplicationasfollows:


publicclassHelloWorld{

publicstaticvoidmain(Stringargs[]){

System.out.println("HellowWorld");

}

}

TheJavaapprequiredsixlinesofcode,whileinScala,wewereabletodothesamewith50%lesscode(threelinesofcode).Thisisaverysimpleapplication.Whenwearecodingcomplexapplications,thisdifferencegetsbigger,asaScalaapplicationendsupwithwaylesscodethanJava.

Remember,weuseanobjectinScalainordertohaveaSingleton(DesignPatternthatmakessureyouhavejustoneinstanceofaclass),andifwewantthesameinJava,thecodewouldbesomethinglikethefollowing:


publicclassHelloWorldSingleton{

privateHelloWorldSingleton(){}

privatestaticclassSingletonHelper{

privatestaticfinalHelloWorldSingletonINSTANCE=

newHelloWorldSingleton();

}

publicstaticHelloWorldSingletongetInstance(){

returnSingletonHelper.INSTANCE;

}

publicvoidsayHello(){

System.out.println("HelloWorld");

}

publicstaticvoidmain(String[]args){

getInstance().sayHello();

}

}

It'snotjustaboutthesizeofthecode,butalsoaboutconsistencyandthelanguageprovidingmoreabstractionsforyou.Ifyouwritelesscode,youwillhavefewerbugsinyoursoftwareattheendoftheday.

Scalalanguage-thebasicsScalaisastaticallytypedlanguagewithaveryexpressivetypesystemwhichenforcesabstractionsinasafeyetcoherentmanner.AllvaluesinScalaareJavaobjects(primitiveswhichareunboxedatruntime),becauseattheendoftheday,ScalarunsontheJavaJVM.ScalaenforcesimmutabilityasacoreFPprinciple.ThisenforcementhappensinmultipleaspectsoftheScalalanguage,forinstance,whenyoucreateavariable,youdoitinanimmutableway,whenyouuseancollection,youwilluseaimmutablecollection.Scalaalsoletsyouusemutablevariablesandmutablestructures,butbydesign,itfavorsimmutableones.

Scalavariables-varandvalWhenyouarecodinginScala,youcreatevariablesusingtheoperatorvar,oryoucanusetheoperatorval.Theoperatorvarallowsyoutocreateamutablestate,whichisfineaslongasyoumakeitlocal,followtheCORE-FPprinciplesandavoidamutablesharedstate.

ScalaREPLvarusageWewillseehowtousevarinScalaREPLasfollows:

$scala



scala>varx=10

x:Int=10

scala>x

res0:Int=10

scala>x=11

x:Int=11

scala>x

res1:Int=11

scala>

However,Scalahasamoreinterestingconstructcalledval.Usingthevaloperatormakesyourvariablesimmutable,andthismeansyoucan'tchangethevalueonceyou'vesetit.IfyoutrytochangethevalueofthevalvariableinScala,thecompilerwillgiveyouanerror.AsaScaladeveloper,youshouldusethevariablevalasmuchaspossible,becausethat'sagoodFPmindset,anditwillmakeyourprogramsbetter.InScala,everythingisanobject;therearenoprimitives--thevarandvalrulesapplyforeverythingitcouldbutanIntorStringorevenaclass.

ScalavalusageattheScalaREPLWewillseehowtousevalinScalaREPLasfollows:

$scala



scala>valx=10

x:Int=10

scala>x

res0:Int=10

scala>x=11

<console>:12:error:reassignmenttoval

x=11

^

scala>x

res1:Int=10

scala>

CreatingimmutablevariablesRightnow,let'sseehowwedefinethemostcommontypesinScalasuchasInt,Double,Boolean,andString.Remember,youcancreatethesevariablesusingvalorvardependingonyourneeds.

ScalavariabletypeintheScalaREPLWewillseeScalavariabletypeinScalaREPLasfollows:

$scala



scala>valx=10

x:Int=10

scala>valy=11.1

y:Double=11.1

scala>valb=true

b:Boolean=true

scala>valf=false

f:Boolean=false

scala>vals="ASimpleString"

s:String=ASimpleString

scala>

Forthevariablesintheprecedingcode,wedidnotdefinethetype.Scalalanguagefiguresitoutforus.However,itispossibletospecifythetypeifyouwant.InScala,thetypecomesafterthenameofthevariable.

ScalavariableswithexplicittypingattheScalaREPLWewillseeScalavariableswithexplicittypingatScalaREPLasfollows:

$scala



scala>valx:Int=10

x:Int=10

scala>valy:Double=11.1

y:Double=11.1

scala>vals:String="MyString"

s:String="MyString"

scala>valb:Boolean=true

b:Boolean=true

scala>

ScalaconditionalandloopsstatementsLikeanyotherlanguage,Scalahassupportforconditionalstatementslikeifandelse.WhileJavahasaswitchstatement,ScalahasamorepowerfulandfunctionalstructurecalledPatternMatcher,whichwewillcoverlaterinthischapter.Scalaallowsyoutouseifstatementsduringvariableassignments,whichisverypracticalaswellasuseful.

IfstatementsinScalaREPLWewillseehowtouseifstatementsinScalaREPLasfollows:

$scala



scala>valx=10

x:Int=10

scala>if(x==10)

|println("Xis10")

Xis10

scala>valy=if(x==10)11

y:AnyVal=11

scala>y

res1:AnyVal=11

scala>

Intheprecedingcode,youcanseethatwesetthevariableybasedonanifcondition.Scalaifconditionsareverypowerful,andtheyalsocanbeusedinreturnstatements.

IfstatementsinreturnstatementsinScalaREPLWewillseehowtouseifstatementsinreturnstatementsinScalaREPLasfollows:

$scala



scala>valx=10

x:Int=10

scala>defsomeFunction=if(x==10)"Xis10"

someFunction:Any

scala>someFunction

res0:Any=Xis10

scala>

Scalasupportselsestatementstoo,andyoualsocanusetheminvariablesandreturnstatementsaswellasfollows:

~$scala



scala>valx=10

x:Int=10

scala>if(x==10){

|println("Xis10")

|}else{

|println("Xissomethingelse")

|}

Xis10

scala>

NowyouwilllearnhowtouseforloopsinScala.ForloopsareverypowerfulinScala.Wewillstartwiththebasicsandlaterwewillmoveontofunctionalloopsusedforcomprehensions,alsoknowasListcomprehensions.

InScala,forloopsworkwithranges,whichisanotherScaladatastructurethatrepresentsnumbersfromastartingpointtoanendpoint.Therangeiscreatedusingtheleftarrowoperator(<-).Scalaallowsyoutohavemultiplerangesinthesameforloopaslongasyouusethesemicolon(;).

Youalsocanuseifstatementsinordertofilterdatainsideforloops,andworksmoothlywithListstructures.Scalaallowsyoutocreatevariablesinsideaforloopaswell.Rightnow,let'sseesomecodewhichillustratesthevariousforloopusagesinScalalanguage.

BasicforloopinScalaREPLWewillseehowtousebasicforloopinScalaREPLasfollows:

$scala



scala>for(i<-1to10)

|println("i*"+i+"="+i*10)

i*1=10

i*2=20

i*3=30

i*4=40

i*5=50

i*6=60

i*7=70

i*8=80

i*9=90

i*10=100

scala>

Rightnow,wewillcreateaforloopusingaScaladatastructurecalledList.Thisisveryuseful,becauseinthefirstlineofcode,youcandefineaListaswellassetitsvaluesinthesameline.SinceweareusingtheListstructure,youdon'tneedtopassanyotherargumentbesidestheListitself.

ForwithListinScalaREPLWewillseehowtouseforwithListinScalaREPLasfollows:

$scala



scala>vallistOfValues=List(1,2,3,4,5,6,7,8,9,10)

listOfValues:List[Int]=List(1,2,3,4,5,6,7,8,9,10)

scala>for(i<-listOfValues)println(i)

1

2

3

4

5

6

7

8

9

10

scala>

Next,wecanuseforloopswithifstatementsinordertoapplysomefiltering.Laterinthisbook,wewillapproachamorefunctionalwaytoapproachfilteringusingfunctions.Forthiscode,let'ssaywewanttogetjusttheevennumbersonthelistandprintthem.

Forwithifstatementsforfiltering-ScalaREPLWewillseehowtouseforwithifstatementsinScalaREPLasfollows:

$scala



scala>vallistOfValues=List(1,2,3,4,5,6,7,8,9,10)

listOfValues:List[Int]=List(1,2,3,4,5,6,7,8,9,10)

scala>for(i<-listOfValues)if(i%2==0)println(i)

2

4

6

8

10

scala>

JavacodeforfilteringevennumbersInScalalanguage,wejustneedtwolinesofcodetoperformthisfiltering,whereasinJavaitwouldhaverequiredatleastelevenlinesofcodeasyouseeinthefollowingcode:


importjava.util.Arrays;

importjava.util.List;

publicclassForLoopsEvenNumberFiltering{


List<Integer>listOfValues=Arrays.asList(

newInteger[]{1,2,3,4,5,6,7,8,9,10});

for(Integeri:listOfValues){

if(i%2==0)System.out.println(i);

}

}

}

ForcomprehensionsAlsoknownaslistorsequencecomprehensions,forcomprehensionsareoneoftheFPwaystoperformloops.ThisisalanguagesupporttocreateListstructureorcollectionsbasedonothercollections.ThistaskisperformedinaSetBuildernotation.AnotherwaytoaccomplishthesamegoalwouldbebyusingtheMapandfilterfunctions,whichwewillcoverlaterinthischapter.Forcomprehensionscanbeusedinageneratorform,whichwouldintroducenewvariablesandvalues,orinareductionistway,whichwouldfiltervaluesresultingintoanewcollectionorsequence.Thesyntaxis:for(expt)yielde,wheretheyieldoperatorwilladdnewvaluestoanewcollection/sequencethatwillbecreatedfromtheoriginalsequence.

ForcomprehensioninScalaREPLWewillseehowtouseforcomprehensioninScalaREPLasfollows:

$scala



scala>valnames=Set("Diego","James","John","Sam","Christophe")

names:scala.collection.immutable.Set[String]=Set(John,Sam,Diego,James,

Christophe)

scala>

scala>valbrazilians=for{

|name<-names

|initial<-name.substring(0,1)

|}yieldif(name.contains("Die"))name

brazillians:scala.collection.immutable.Set[Any]=Set((),Diego)

scala>

Intheprecedingcode,wecreateasetofnames.Asyoucansee,Scala,bydefault,prefersimmutabledatastructuresandusesimmutable.Set.Whenweapplytheforloop,wearesimplyfilteringonlythenameswhichcontainaspecificsubstring,andthen,usingtheyieldoperator,wearecreatinganewSetstructure.Theyieldoperatorwillkeepthestructureyouareusing.Forinstance,ifweuseListstructure,itwouldcreateaListinsteadofaSetstructure,theyieldoperatorwillalwayskeepthesamedatacollectionyouhaveonthevariable.AnotherinterestingaspectoftheprecedingcodeisthefactthatweareholdingtheresultoftheforcomprehensioninavariablecalledBrazilians.Javadoesnothaveforcomprehensions,butwecouldusesimilarcodealthoughitwouldrequirewaymorelinesofcode.

JavacodeforperformingfilteringwithcollectionsWewillseehowtouseJavacodeforperformingfilteringwithcollectionsasfollows:


importjava.util.LinkedHashSet;

importjava.util.Set;

publicclassJavaNoForComprehension{


Set<String>names=newLinkedHashSet<>();

Set<String>brazillians=newLinkedHashSet<>();

names.add("Diego");

names.add("James");

names.add("John");

names.add("Sam");

names.add("Christophe");

for(Stringname:names){

if(name.contains("Die"))brazillians.add(name);

}

System.out.println(brazillians);

}

}

ScalacollectionsIntheprevioussection,wesawhowtocreatetheListandSetstructuresinScalainanimmutableway.NowwewilllearntoworkwiththeListandSetstructuresinamutableway,andalsowithothercollectionssuchassequences,tuples,andMaps.Let'stakealookattheScalacollectionshierarchytree,asshowninthefollowingdiagram:

Nowlet'stakealookattheScalaSeqclasshierarchy.Asyoucansee,Seqistraversableaswell.

Scalacollectionsextendfromtraversable,whichisthemaintraitofallcollection'sdescends.Liststructures,forinstance,extendfromSeqclasshierarchy,whichmeanssequence-Listisakindofsequence.AllthesetreesareimmutableormutabledependingontheScalapackageyouendupusing.

Let'sseehowtoperformbasicmutableoperationswithListstructuresinScala.Inordertohavefilterandremovaloperations,weneeduseaBuffersequenceasfollows:

$scala



scala>varms=scala.collection.mutable.ListBuffer(1,2,3)

ms:scala.collection.mutable.ListBuffer[Int]=ListBuffer(1,2,3)

scala>ms+=4

res0:scala.collection.mutable.ListBuffer[Int]=ListBuffer(1,2,3,4)

scala>ms+=5

res1:scala.collection.mutable.ListBuffer[Int]=ListBuffer(1,2,3,4,5)

scala>ms+=6

res2:scala.collection.mutable.ListBuffer[Int]=ListBuffer(1,2,3,4,5,6)

scala>ms(1)

res3:Int=2

scala>ms(5)

res4:Int=6

scala>ms-=5

res5:scala.collection.mutable.ListBuffer[Int]=ListBuffer(1,2,3,4,6)

scala>ms-=6

res6:scala.collection.mutable.ListBuffer[Int]=ListBuffer(1,2,3,4)

scala>

Let'sseethenextsetofcode.

Creating,removing,andgettinganitemfromamutablelistinScalaREPLWewillseehowtocreate,remove,andgetanitemfromamutablelistinScalaREPLasfollows:

$scala



scala>varnames=scala.collection.mutable.SortedSet[String]("Diego",

"Poletto","Jackson")

names:scala.collection.mutable.SortedSet[String]=TreeSet(Diego,Jackson,

Poletto)

scala>names+="Sam"

res2:scala.collection.mutable.SortedSet[String]=TreeSet(Diego,Jackson,

Poletto,Sam)

scala>names("Diego")

res4:Boolean=true

scala>names-="Jackson"

res5:scala.collection.mutable.SortedSet[String]=TreeSet(Diego,Poletto,

Sam)

scala>

Haveyoueverwantedtoreturnmultiplevaluesinamethod?Well,inJavayouhavetocreateaclass,butinScala,thereisamoreconvenientwaytoperformthistask,andyouwon'tneedtocreatenewclasseseachtime.Tuplesallowyoutoreturnorsimplyholdmultiplevaluesinmethodswithouthavingtocreateaspecifictype.

ScalatuplesWewillseeScalatuplesasfollows:

$scala



scala>valconfig=("localhost",8080)

config:(String,Int)=(localhost,8080)

scala>config._1

res0:String=localhost

scala>config._2

res1:Int=8080

scala>

Scalahasspecialmethodscalled_1and_2whichyoucanusetoretrieveatuple'svalues.Theonlythingyouhavetokeepinmindisthefactthatvaluesarekeptintheorderofinsertioninthetuple.

Scalahasaverypracticalandusefulcollectionlibrary.AMap,forinstance,isakey/valuepairthatcanberetrievedbasedonthekey,whichisunique.However,Mapvaluesdonotneedtobeunique.LikeotherScalacollections,youhavemutableandimmutableMapcollections.KeepinmindthatScalafavorsimmutablecollectionsovermutableones.

ScalaimmutableMapinScalaREPLWewillseeScalaimmutableMapinScalaREPLasfollows:

$scala



scala>valnumbers=Map("one"->1,

|"two"->2,

|"three"->3,

|"four"->4,

|"five"->5,

|"six"->6,

|"seven"->7,

|"eight"->8,

|"nine"->9,

|"ten"->10)

numbers:scala.collection.immutable.Map[String,Int]=Map(four->4,three->

3,two->2,six->6,seven->7,ten->10,five->5,nine->9,one->1,

eight->8)

scala>

scala>numbers.keys

res0:Iterable[String]=Set(four,three,two,six,seven,ten,five,nine,

one,eight)

scala>

scala>numbers.values

res1:Iterable[Int]=MapLike(4,3,2,6,7,10,5,9,1,8)

scala>

scala>numbers("one")

res2:Int=1

scala>

Asyoucansee,Scalausesscala.collection.immutable.MapwhenyoucreateaMapusingMap().Bothkeysandvaluesareiterable,andyoucanhaveaccesstoallthekeyswiththekeysmethodortoallthevaluesusingthevaluesmethod.

ScalamutableMapsatScalaREPLWewillseeScalamutableMapinScalaREPLasfollows:

$scala



scala>valmap=scala.collection.mutable.HashMap.empty[Int,String]

map:scala.collection.mutable.HashMap[Int,String]=Map()

scala>map+=(1->"one")

res0:map.type=Map(1->one)

scala>map+=(2->"two")

res1:map.type=Map(2->two,1->one)

scala>map+=(3->"three")

res2:map.type=Map(2->two,1->one,3->three)

scala>map+=(4->"mutable")

res3:map.type=Map(2->two,4->mutable,1->one,3->three)

scala>

Ifyouaredealingwithmutablestate,youhavetobeexplicitandthisisgreatinScala,becauseitincreasesdevelopers'awarenessandavoidsmutablesharedstatebydefault.So,inordertohaveamutableMap,weneedtoexplicitlycreatetheMapwithscala.collection.mutable.HashMap.

MonadsMonadsarecombinableparametrizedcontainertypeswhichhavesupportforhigher-orderfunctions.Rememberhigher-orderfunctionsarefunctionswhichreceivefunctionsasparametersandreturnfunctionsasresults.OneofthemostusedfunctionsinFPisMap.Maptakesafunction,appliesittoeachelementinthecontainer,andreturnsanewcontainer.

ScalaMapfunctioninScalaREPLWewillseeMapfunctioninScalaREPLasfollows:

$scala



scala>

scala>valnumbers=List(1,2,3,4,5,6)

numbers:List[Int]=List(1,2,3,4,5,6)

scala>defdoubleIt(i:Int):Double=i*2

doubleIt:(i:Int)Double

scala>valdoubled=numbers.map(doubleIt_)

doubled:List[Double]=List(2.0,4.0,6.0,8.0,10.0,12.0)

scala>valdoubled=numbers.map(2.0*_)

doubled:List[Int]=List(2.0,4.0,6.0,8.0,10.0,12.0)

scala>

Intheprecedingcode,wecreatedalistofnumberscontaining1,2,3,4,5,and6.WealsodefinedaScalafunctioncalleddoubleIt,whichreceivesanintegerandmultipliesitby2.0resultinginadoublenumber.ThemapfunctioncallsdoubleItforeachelementintheList(1,2,3,4,5,6),andtheresultisanewcontainer,abrandnewListinstancecontainingthenewvalues.

Scalahassomesyntacticalsugarwhichhelpsustobemoreproductive.Forinstance,youmayrealizethatinthepreviouscode,wealsodid-2.0*_.Theunderscoreisaspecialoperatorforthisspecificcase--itmeansthecurrentvalueisbeingiteratedintothecollection.Scalawillcreateafunctionfromthisexpressionforus.

Asyoumighthaverealized,mapfunctionsareprettyusefulforlotsofreasons:onereasonisthatyoucandocomplexcomputationswithoutusingtheforloopexplicitly,andthismakesyourcodefunctional.Secondly,wecanuseamapfunctiontoconvertelementtypesfromonetypetoanother.That'swhatwedidinthepreviouscode:wetransformedalistofintegersintoalistofdoubles.Lookatthefollowing:

scala>valone=Some(1)

one:Some[Int]=Some(1)

scala>valoneString=one.map(_.toString)

oneString:Option[String]=Some(1)

Themapfunctionoperatesoverseveraldatastructuresandnotonlycollections,asyoucanseeinthepreviouscode.YoucanusethemapfunctiononprettymucheverythinginScalalanguage.

Themapfunctionisgreat,butyoucanendupwithnestedstructures.That'swhy,whenweareworkingwithMonads,weuseaslightlydifferentversionofthemapfunctioncalledflatMap,whichworksinaverysimilarwaytothemapfunction,butreturnsthevaluesinaflatforminsteadofnestedvalues.

Inordertohaveamonad,youneedtohaveamethodcalledflatMap.OtherfunctionlanguagessuchasHaskellcallflatMapasbind,andusetheoperator>>=.Thesyntaxchangeswiththelanguage,buttheconceptisthesame.

Monadscanbebuiltindifferentways.InScala,weneedasingleargumentconstructorwhichwillworkasamonadfactory.Basically,theconstructorreceivesonetype,A,andreturnsMonad[A]orjustM[A].Forinstance,unit(A)foraListwillbe==List[A]andunit(A),whereaisanOption==Option[A].InScala,youdon'tneedtohaveunit;thisisoptional.TohaveamonadinScala,youneedtohavemapandflatMapimplemented.

WorkingwithMonadswillmakeyouwritealittlebitmorecodethanbefore.However,youwillgetawaybetterAPI,whichwillbeeasiertoreuseandyourpotentialcomplexitywillbemanaged,becauseyouwon'tneedtowriteacomplexcodefullofifandforloops.Thepossibilitiesareexpressedthroughthetypes,andthecompilercancheckitforyou.LetusseeasimplemonadexampleinScalalanguage:

OptionMonadinScalaWewillseeoptionMonadinScalaasfollows:

$scala



scala>vala:Option[Int]=Some(1)

a:Option[Int]=Some(1)

scala>a.get

res0:Int=1

scala>valb:Option[Int]=None

b:Option[Int]=None

scala>b.get

java.util.NoSuchElementException:None.get

atscala.None$.get(Option.scala:347)

atscala.None$.get(Option.scala:345)

...32elided

scala>b.getOrElse(0)

res2:Int=0

scala>a==b

res3:Boolean=false

scala>

InHaskell,thisalsoknownastheMaybemonad.Optionmeansoptionalvalue,becausewearenot100%sureifthevaluewillbepresent.Inordertoexpressavalue,weusetheSometype,andinordertoexpressthelackofvalue,weusenone.OptionMonadsaregreat,theymakeyourcodemoreexplicit,becauseamethodmightreceiveorreturnanoption,whichmeansyouareexplicitlysayingthiscouldbenull.However,thistechniqueisnotonlymoreexpressivebutalsosafer,sinceyouwon'tgetanullpointer,becauseyouhaveacontaineraroundthevalue.Although,ifyoucallthemethodgetinOptionanditisnone,youwillgetaNoSuchelementException.Inordertofixthis,youcanusethemethodgetOrElse,andyoucansupplyafallbackvaluewhichwillbeusedinthecaseofnone.Alright,butyoumightbewonderingwheretheflatMapmethodis.Don'tworry,ScalaimplementsthismethodforusintotheOptionabstraction,soyoucanuseitwithnoissues.

scala>valc=Some("one")

c:Some[String]=Some(one)

scala>c.flatMap(s=>Some(s.toUpperCase))

res6:Option[String]=Some(ONE)

TheScalaREPLcanperformautocompleteforyou.IfyoutypeC+Tab,youwillseealltheavailablemethodsfortheSomeclass.Themapfunctionisavailableforyoutouse,andasIsaidbefore,thereisnounitfunctioninScalawhatsoever.However,itisnotwrongifyouaddinyourAPIs.

AlistofallmethodsusingtheScalaREPLFollowingarethelistofallmethodsusingtheScalaREPL:

$scala



scala>valc=Some("one")

c:Some[String]=Some(one)

scala>c.

++countforeachiteratorproductArity

seqtoBufferunzip

++:dropgenericBuilderlastproductElement

sizetoIndexedSequnzip3

/:dropRightgetlastOptionproductIterator

slicetoIterableview

:\dropWhilegetOrElsemapproductPrefix

slidingtoIteratorwithFilter

WithFilterequalsgroupBymax

reducespantoLeftx

addStringexistsgroupedmaxBy

reduceLeftsplitAttoListzip

aggregatefilterhasDefiniteSizeminreduceLeftOption

stringPrefixtoMapzipAll

canEqualfilterNothashCodeminByreduceOption

sumtoRightzipWithIndex

collectfindheadmkStringreduceRight

tailtoSeq

collectFirst

flatMapheadOptionnonEmptyreduceRightOptiontails

toSet

companionflatten

initorElsereprtake

toStream

containsfoldinitsorNull

sameElementstakeRighttoString

copyfoldLeftisDefinedpar

scantakeWhiletoTraversable

copyToArrayfoldRightisEmptypartitionscanLeft

totoVector

copyToBufferforallisTraversableAgainproductscanRight

toArray

transpose

scala>c

Scalaclass,traits,andOOprogrammingAsahybridpost-functionallanguage,ScalaallowsyoutowriteOOcodeandcreateclassesaswell.Rightnowwewilllearnhowtocreateclassesandfunctionsinsideclasses,andalsohowtoworkwithtraits,whicharesimilartoJavainterfacesinconceptbutwaymorepowerfulinpractice.

AsimpleScalaclassinScalaREPLWewillseeasimpleScalaclassinScalaREPLasfollows:

$scala



scala>classCalculator{

|defadd(a:Int,b:Int):Int=a+b

|defmultiply(n:Int,f:Int):Int=n*f

|}

definedclassCalculator

scala>

scala>valc=newCalculator

c:Calculator=Calculator@380fb434

scala>c.add(1,2)

res0:Int=3

scala>c.multiply(3,2)

res1:Int=6

scala>

Atfirstglance,theprecedingcodelookslikeJava.Butlet'saddconstructors,getters,andsetters,andthenyoucanseehowmuchwecanaccomplishwithjustafewlinesofcode.

ScalaplainoldJavaobjectinScalaREPLFollowingisaScalaplainoldJavaobjectinScalaREPL:

$scala



scala>classPerson(

|@scala.beans.BeanPropertyvarname:String="",

|@scala.beans.BeanPropertyvarage:Int=0

|){

|name=name.toUpperCase

|overridedeftoString="name:"+name+"age:"+age

|}

definedclassPerson

scala>

scala>valp=newPerson("Diego",31)

p:Person=name:DIEGOage:31

scala>valp1=newPerson(age=31,name="Diego")

p1:Person=name:DIEGOage:31

scala>p.getAge

res0:Int=31

scala>p1.getName

res1:String=DIEGO

scala>

ConstructorsinScalaarejustlinesofcode.Youmightrealizethatwegetthenamevariable,andapplyafunctiontochangethegivennametouppercaseintheprecedingexample.Ifyouwant,youcanputasmanylinesasyouwant,andyoucanperformasmanycomputationsasyouwish.

Onthissamecode,weperformmethodoverridingaswell,becauseweoverridethetoStringmethod.InScala,inordertodoanoverride,youneedtousetheoverrideoperatorinfrontofthefunctiondefinition.

WejustwroteaPlainOldJavaObject(POJO)withveryfewlinesofcodeinScala.Scalahasaspecialannotationcalled@scala.beans.BeanProperty,whichgeneratesthegetterandsettermethodforyou.Thisisveryuseful,andsaveslotsoflinesofcode.However,thetargetneedstobepublic;youcan'taapplyBeanPropertyannotationontopofaprivatevarorvalobject.

PersonclassinJavaFollowingisaPersonclassinJava:


publicclassJavaPerson{

privateStringname;

privateIntegerage;

publicJavaPerson(){}

publicJavaPerson(Stringname,Integerage){

super();

this.name=name;

this.age=age;

}

publicJavaPerson(Stringname){

super();

this.name=name;

}

publicJavaPerson(Integerage){

super();

this.age=age;

}

publicIntegergetAge(){

returnage;

}

publicvoidsetAge(Integerage){

this.age=age;

}

publicStringgetName(){

returnname;

}

publicvoidsetName(Stringname){

this.name=name;

}

}

TraitsandinheritanceIt'spossibletodoinheritanceinScalaaswell.Forsuchatask,youusetheoperatorextendaftertheclassdefinition.Scalajustallowsyoutoextendoneclass,justlikeJava.JavadoesnotallowmultipleinheritancelikeC++.However,ScalaallowsitbyusingtheMixingtechniquewithtraits.ScalatraitsarelikeJavainterface,butyoucanalsoaddconcretecode,andyouareallowedtohaveasmanytraitsasyouwantinyourcode.

ScalainheritancecodeinScalaREPLFollowingisaScalainheritancecodeinScalaREPL:

$scala



scala>classPerson(

|@scala.beans.BeanPropertyvarname:String="",

|@scala.beans.BeanPropertyvarage:Int=0

|){

|name=name.toUpperCase

|overridedeftoString="name:"+name+"age:"+age

|}

definedclassPerson

scala>

scala>classLowerCasePerson(name:String,age:Int)extendsPerson(name,age){

|setName(name.toLowerCase)

|}

definedclassLowerCasePerson

scala>

scala>valp=newLowerCasePerson("DIEGOPACHECO",31)

p:LowerCasePerson=name:diegopachecoage:31

scala>p.getName

res0:String=diegopacheco

scala>

ScaladoesnotmakeconstructorsinheritancelikeJava.Soyouneedtorewritetheconstructorsandpassthevaluesthroughasuperclass.Allcodeinsidetheclasswillbethesecondaryconstructor.Allcodeinsideparentheses()intheclassdefinitionwillbetheprimaryconstructor.It'spossibletohavemultipleconstructorsusingthethisoperator.Forthisparticularimplementation,wechangedthedefaultbehaviorandaddednewconstructorcodeinordertomakethegivennamelowercase,insteadofthedefaultuppercasedefinedbythePersonsuperclass.

ScalatraitssamplecodeinScalaREPLFollowingisaScalatraitssamplecodeinScalaREPL:

$scala



scala>traitCar

definedtraitCar

scala>

scala>traitSportCar{

|valbrand:String

|defrun():String="RghhhhhRghhhhhRghhhhh...."

|}

definedtraitSportCar

scala>

scala>traitPrintable{

|defprintIt:Unit

|}

definedtraitPrintable

scala>

scala>classBMWextendsCarwithSportCarwithPrintable{

|overridevalbrand="BMW"

|overridedefprintIt:Unit=println(brand+"does"+run())

|}

definedclassBMW

scala>

scala>valx1=newBMW

x1:BMW=BMW@22a71081

scala>x1.printIt

BMWdoesRghhhhhRghhhhhRghhhhh....

scala>

Intheprecedingcode,wecreatedmultipletraits.OneiscalledCar,whichisthemothertrait.Traitssupportinheritanceaswell,andwehaveitwiththeSportCartraitwhichextendsfromtheCartrait.TheSportCartraitdemandsavariablecalledbrand,anddefinesaconcreteimplementationofthefunctionrun.Finally,wehaveaclasscalledBMWwhichextendsfrommultipletraits--thistechniqueiscalledmixing.

ScalatraitsusingvariablemixingtechniqueatScalaREPLFollowingisaScalatraitsusingvariablemixingtechniqueatScalaREPL:

$scala



scala>traitSportCar{

|defrun():String="RghhhhhRghhhhhRghhhhh...."

|}

definedtraitSportCar

scala>

scala>valbmw=newObjectwithSportCar

bmw:SportCar=$anon$1@ed17bee

scala>bmw.run

res0:String=RghhhhhRghhhhhRghhhhh....

scala>

Scalaisaverypowerfullanguageindeed.It'spossibletoaddtraitstoavariableatruntime.Whenyoudefineavariable,youcanusethewithoperatoraftertheassignment.Thisisaveryusefulfeature,becauseitmakesiteasiertomakefunctioncomposition.Youcanhavemultiplespecializedtraitsandjustaddtheminyourvariablesasyouneedthem.

Scalaallowsyoutocreatethetypealiasaswell,thisisaverysimpletechniquewhichwillincreasethereadabilityofyourcode.It'sjustasimplealias.

ScalatypealiassampleinScalaREPLFollowingisaScalatypealiassampleinScalaREPL:

$scala



scala>typeEmail=String

definedtypealiasEmail

scala>

scala>vale=newEmail("[email protected]")

e:[email protected]

scala>

WhenyouarecodingwithScala,itishighlyrecommendedthatyouusethetypealiasandtraitsforeverything,becausethatwayyouwillgetmoreadvantageswithyourcompiler,andyouwillavoidwritingunnecessarycodeandunnecessaryunittests.

CaseclassesWearenotdoneyetintermsoftheOOfeaturesinScala;thereisanotherveryinterestingwaytoworkwithclassesinScala:theso-calledcaseclasses.CaseclassesaregreatbecauseyoucanhaveaclasswithwaylessnumberoflinesofcodeandcaseclassescanbepartofaPatternMatcher.

ScalacaseclassesfeatureinScalaREPLFollowingisaScalacaseclassesfeatureinScalaREPL:

$scala



scala>caseclassPerson(name:String,age:Int)

definedclassPerson

scala>valp=Person("Diego",31)

p:Person=Person(Diego,31)

scala>valp2=Person("Diego",32)

p2:Person=Person(Diego,32)

scala>p.name

res0:String=Diego

scala>p.age

res1:Int=31

scala>p==p

res2:Boolean=true

scala>p.toString

res3:String=Person(Diego,31)

scala>p.hashCode

res4:Int=668670772

scala>p.equals(p2)

res5:Boolean=false

scala>p.equals(p)

res6:Boolean=true

scala>

ThisistheScalawaytoworkwithclasses.Becausethisissomucheasierandcompact,youprettymuchcreateaclasswithonelineofcode,andyoucanhavetheequalsandhashcodemethodsforfree.

PatternMatcherWhenyoucodeinJava,youcanuseaSwitchstatement.However,inScala,wehaveamorepowerfulfeaturecalledPatternMatcher,whichisakindofswitchbutonsteroids.

SimplePatternMatcherinScalaFollowingisaSimplePatternMatcherinScala:

$scala



scala>defresolve(choice:Int):String=choicematch{

|case1=>"yes"

|case0=>"no"

|case_=>thrownewIllegalArgumentException("Validargumentsare:

0or1.Yourargis:

"+choice)

|}

resolve:(choice:Int)String

scala>println(resolve(0))

no

scala>println(resolve(1))

yes

scala>try{

|println(resolve(33))

|}catch{

|casee:Exception=>println("SomethingWentWorng.EX:"+e)

|}

SomethingWentWorng.EX:java.lang.IllegalArgumentException:Validarguments

are:0or1.Yourargis:33

scala>

ScalausesPatternMatcherforerrorhandling.JavadoesnothavePatternMatcherlikeScala.It'ssimilartoaswitchstatement;however,PatternMatchercanbeusedinamethodreturnstatementasyoucanseeintheprecedingcode.Scaladeveloperscanspecifyaspecialoperatorcalled_(Underscore),whichallowsyoutospecifyanythinginthePatternMatcherscope.Thisbehaviorissimilartoelseinanifconditional.However,inScala,youcanuse_inseveralplaces,andnotonlyastheotherwiseclause,likeinJavaswitch.

ErrorhandlinginScalaissimilartoerrorhandlinginJava.Weusetry...catchblocks.ThemaindifferenceisthatyouhavetousePatternMatcherinScala,whichisgreatbecauseitaddsmoreflexibilitytoyourcode.PatternMatcherinScalacanoperateagainstmanydatastructureslikecaseclasses,collections,integers,andstrings.

Theprecedingcodeisprettysimpleandstraightforward.NextwewillseeamorecomplexandadvancedcodeusingtheScalaPatternMatcherfeature.

AdvancedpatternmatcherinScalaREPLFollowingisanAdvancedPatternMatcherusingScalaREPL:

$scala



scala>deffactorial(n:Int):Int=nmatch{

|case0=>1

|casen=>n*factorial(n-1)

|}

factorial:(n:Int)Int

scala>

scala>println(factorial(3))

6

scala>println(factorial(6))

720

scala>

PatternMatchercanbeusedinaveryfunctionalway.Forinstance,intheprecedingcode,weusethePatternMatcherforrecursion.Thereisnoneedtocreateavariabletostoretheresult,wecanputthePatternMatcherstraighttothefunctionreturn,whichisveryconvenientandsaveslotsoflinesofcode.

AdvancedcomplexpatternmatcherinScalaREPLFollowingisanAdvancedcomplexPatternMatcherusingScalaREPL:

$scala



scala>traitColor

definedtraitColor

scala>caseclassRed(saturation:Int)extendsColor

definedclassRed

scala>caseclassGreen(saturation:Int)extendsColor

definedclassGreen

scala>caseclassBlue(saturation:Int)extendsColor

definedclassBlue

scala>defmatcher(arg:Any):String=argmatch{

|case"Scala"=>"AAwesomeLanguage"

|casex:Int=>"AnIntwithvalue"+x

|caseRed(100)=>"Redsat100"

|caseRed(_)=>"AnykindofREDsat"

|caseGreen(s)ifs==233=>"Greensat233"

|caseGreen(s)=>"Greensat"+s

|casec:Color=>"SomeColor:"+c

|casew:Any=>"Whatever:"+w

|}

matcher:(arg:Any)String

scala>println(matcher("Scala"))

AAwesomeLanguage

scala>println(matcher(1))

AnIntwithvalue1

scala>println(matcher(Red(100)))

Redsat100

scala>println(matcher(Red(160)))

AnykindofREDsat

scala>println(matcher(Green(160)))

Greensat160

scala>println(matcher(Green(233)))

Greensat233

scala>println(matcher(Blue(111)))

SomeColor:Blue(111)

scala>println(matcher(false))

Whatever:false

scala>println(matcher(newObject))

Whatever:java.lang.Object@b56c222

scala>

TheScalaPatternMatcherisreallyamazing.WejustusedanifstatementinthemiddleofthePatternMatcher,andalso_tospecifyamatchforanykindofredvalue.WealsousedcaseclassesinthemiddleofthePatternMatcherexpressions.

PartialfunctionsPartialfunctionsaregreatforfunctioncomposition.TheycanoperatewithcasestatementsaswejustlearnedfromPatternMatcher.Partialfunctionsaregreatinthesenseoffunctioncomposition.Theyallowustodefineafunctioninsteps.Scalaframeworksandlibrariesusethisfeaturealottocreateabstractionsandcallbackmechanisms.It'salsopossibletocheckifapartialfunctionisbeingsuppliedornot.

Partialfunctionsarepredictable,becausethecallercancheckbeforehandifthevaluewillbeappliedtothepartialfunctionornot.Partialfunctioncanbecodedwithorwithoutcase-likestatements.

SimplePartialfunctioninScalaREPLFollowingisasimplePartialfunctionusingScalaREPL:

$scala



scala>valpositiveNumber=newPartialFunction[Int,Int]{

|defapply(n:Int)=n/n

|defisDefinedAt(n:Int)=n!=0

|}

positiveNumber:PartialFunction[Int,Int]=<function1>

scala>

scala>println(positiveNumber.isDefinedAt(6))

true


false

scala>

scala>println(positiveNumber(6))

1


java.lang.ArithmeticException:/byzero

at$anon$1.apply$mcII$sp(<console>:12)

...32elided

scala>

PartialfunctionsareScalaclasses.Theyhavesomemethodsyouneedtoprovide,forinstance,applyandisDefinedAt.ThefunctionisDefinedAtisusedbythecallertocheckifthePartialFunctionwillacceptandoperatewiththevaluesupplied.TheapplyfunctionwilldotheworkwhenthePartialFunctionisexecutedbyScala.

ScalaPartialFunctionwithoutOOusingcasestatementsinScalaREPLFollowingisaScalaPartialFunctionwithoutOOusingcasestatementsinScalaREPL:

$scala



scala>valpositiveNumber:PartialFunction[Int,Int]={

|casen:Intifn!=0=>n/n

|}

positiveNumber:PartialFunction[Int,Int]=<function1>

scala>


true


false

scala>


1


scala.MatchError:0(ofclassjava.lang.Integer)

atscala.PartialFunction$$anon$1.apply(PartialFunction.scala:253)

atscala.PartialFunction$$anon$1.apply(PartialFunction.scala:251)

at$anonfun$1.applyOrElse(<console>:11)

at$anonfun$1.applyOrElse(<console>:11)

atscala.runtime.AbstractPartialFunction$mcII$sp.apply$mcII$sp

(AbstractPartialFunction.scala:36)

...32elided

scala>

ScalawasamorefluentwaytoworkwithPartialFunctionusingthecasestatements.Whenyouusethecasestatements,youdon'tneedtosupplytheapplyandisDefinedAtfunctions,sincethePatternMatchertakescareofthat.

PartialFunctioncompositioninScalaREPLFollowingisaPartialFunctioncompositioninScalaREPL:

$scala



scala>valeven:PartialFunction[Int,String]={

|caseiifi%2==0=>"even"

|}

even:PartialFunction[Int,String]=<function1>

scala>

scala>valodd:PartialFunction[Int,String]={case_=>"odd"}

odd:PartialFunction[Int,String]=<function1>

scala>

scala>valevenOrOdd:(Int=>String)=evenorElseodd

evenOrOdd:Int=>String=<function1>

scala>

scala>println(evenOrOdd(1)=="odd")

true

scala>println(evenOrOdd(2)=="even")

true

scala>

ScalaallowsustocomposeasmanyPartialFunctionsaswewant.PartialFunctioncompositionhappenswiththeorElsefunction.Intheprecedingcode,wedefinedanimmutablevariablecalledeven,whichverifiesevennumbers.Secondly,wecreatedasecondimmutablevariablecalledodd,whichchecksforoddnumbers.Thenwedidthecomposition,andcreatedathirdPartialFunctioncalledevenOrOddwithcomposeevenandoddusingtheorElseoperator.

PackageobjectsScalahaspackageslikeJava.However,Scalapackagesarealsoobjects,andyoucanhavecodeinsideapackage.JavadoesnothavethesamepowerasScalaintermsofpackages.Ifyouaddcodetoapackage,itwillbeavailabletoallclassesandfunctionswithinthatpackage.

package.scalaYourpackage.scalafileshouldcontainthefollowingcode

packagecom.packait.scala.book

packageobjectcommons{

valPI=3.1415926

objectconstraintsHolder{

valODD="Odd"

valEVEN="Even"

}

defisOdd(n:Int):String=if(n%2==0)constraintsHolder.ODDelse

null

defisEven(n:Int):String=if(n%2!=0)constraintsHolder.EVEN

elsenull

defshow(s:String)=println(s)

}

ThisistheScalapackageobject.Thereisthisspecialtokencalledpackageobjectwhichyouusetodefinecommoncodetoallclasses,objects,andfunctionsthataredefinedinsidethispackageorsub-package.Forthiscase,wedefineavalueofPIasaconstantandalsooneobjectholdercontainingtheStringvaluesforOddandEven.Therearealsothreehelperfunctions,whichcanandwillbeusedbytheclassesinsidethispackage.

MainApp.scalaYourMainApp.scalafileshouldcontainthefollowingcode

packagecom.packait.scala.book.commons

objectMainAppextendsApp{

show("PIis:"+PI)

show(constraintsHolder.getClass.toString())

show(isOdd(2))

show(isOdd(6))

show(isEven(3))

show(isEven(7))

}

Asyoucanseeintheprecedingcode,thisnewobjectisplacedinthepackage:com.packait.scala.book.commons.Anotherinterestingthingisthefactthatwedon'thaveanyimportstatementherebecauseofthepackageobjectfeature.Whenyoucompileandrunthisprogram,youwillseethefollowingoutput:

PIis:3.1415926

classcom.packait.scala.book.commons.package$constraintsHolder$

Odd

Odd

Even

Even

ScalausesthePackageobjectagreatdealprovidinglotsofshortcutsandconvenienceforallScaladevelopers.ThefollowingistheScalapackageobjectdefinition:

/*__

*\

**___________//___ScalaAPI

**

**/__/__//_|///_|(c)2003-2013,LAMP/EPFL

**

**__\\//__/__|//__/__|http://scala-lang.org/

**

**/____/\___/_/|_/____/_/||

**

**|/

**

\*

*/

/**

*CoreScalatypes.Theyarealwaysavailablewithoutanexplicit

import.

*@contentDiagramhideNodes"scala.Serializable"

*/

packageobjectscala{

typeThrowable=java.lang.Throwable

typeException=java.lang.Exception

typeError=java.lang.Error

typeRuntimeException=java.lang.RuntimeException

typeNullPointerException=

java.lang.NullPointerException

typeClassCastException=

java.lang.ClassCastException

typeIndexOutOfBoundsException=

java.lang.IndexOutOfBoundsException

typeArrayIndexOutOfBoundsException=

java.lang.ArrayIndexOutOfBoundsException

typeStringIndexOutOfBoundsException=

java.lang.StringIndexOutOfBoundsException

typeUnsupportedOperationException=

java.lang.UnsupportedOperationException

typeIllegalArgumentException=

java.lang.IllegalArgumentException

typeNoSuchElementException=

java.util.NoSuchElementException

typeNumberFormatException=

java.lang.NumberFormatException

typeAbstractMethodError=

java.lang.AbstractMethodError

typeInterruptedException=

java.lang.InterruptedException

//Adummyusedbythespecializationannotation.

valAnyRef=newSpecializable{

overridedeftoString="objectAnyRef"

}

typeTraversableOnce[+A]=scala.collection.TraversableOnce[A]

typeTraversable[+A]=scala.collection.Traversable[A]

valTraversable=scala.collection.Traversable

typeIterable[+A]=scala.collection.Iterable[A]

valIterable=scala.collection.Iterable

typeSeq[+A]=scala.collection.Seq[A]

valSeq=scala.collection.Seq

typeIndexedSeq[+A]=scala.collection.IndexedSeq[A]

valIndexedSeq=scala.collection.IndexedSeq

typeIterator[+A]=scala.collection.Iterator[A]

valIterator=scala.collection.Iterator

typeBufferedIterator[+A]=scala.collection.BufferedIterator[A]

typeList[+A]=scala.collection.immutable.List[A]

valList=scala.collection.immutable.List

valNil=scala.collection.immutable.Nil

type::[A]=scala.collection.immutable.::[A]

val::=scala.collection.immutable.::

val+:=scala.collection.+:

val:+=scala.collection.:+

typeStream[+A]=scala.collection.immutable.Stream[A]

valStream=scala.collection.immutable.Stream

val#::=scala.collection.immutable.Stream.#::

typeVector[+A]=scala.collection.immutable.Vector[A]

valVector=scala.collection.immutable.Vector

typeStringBuilder=scala.collection.mutable.StringBuilder

valStringBuilder=scala.collection.mutable.StringBuilder

typeRange=scala.collection.immutable.Range

valRange=scala.collection.immutable.Range

//Numerictypeswhichweremovedintoscala.math.*

typeBigDecimal=scala.math.BigDecimal

valBigDecimal=scala.math.BigDecimal

typeBigInt=scala.math.BigInt

valBigInt=scala.math.BigInt

typeEquiv[T]=scala.math.Equiv[T]

valEquiv=scala.math.Equiv

typeFractional[T]=scala.math.Fractional[T]

valFractional=scala.math.Fractional

typeIntegral[T]=scala.math.Integral[T]

valIntegral=scala.math.Integral

typeNumeric[T]=scala.math.Numeric[T]

valNumeric=scala.math.Numeric

typeOrdered[T]=scala.math.Ordered[T]

valOrdered=scala.math.Ordered

typeOrdering[T]=scala.math.Ordering[T]

valOrdering=scala.math.Ordering

typePartialOrdering[T]=scala.math.PartialOrdering[T]

typePartiallyOrdered[T]=scala.math.PartiallyOrdered[T]

typeEither[+A,+B]=scala.util.Either[A,B]

valEither=scala.util.Either

typeLeft[+A,+B]=scala.util.Left[A,B]

valLeft=scala.util.Left

typeRight[+A,+B]=scala.util.Right[A,B]

valRight=scala.util.Right

//Annotationswhichwemightmovetoannotation.*

/*

typeSerialVersionUID=annotation.SerialVersionUID

typedeprecated=annotation.deprecated

typedeprecatedName=annotation.deprecatedName

typeinline=annotation.inline

typenative=annotation.native

typenoinline=annotation.noinline

typeremote=annotation.remote

typespecialized=annotation.specialized

typetransient=annotation.transient

typethrows=annotation.throws

typeunchecked=annotation.unchecked.unchecked

typevolatile=annotation.volatile

*/

}

FunctionsLikeanygreatFPlanguage,Scalahaslotsofbuilt-infunctions.Thesefunctionsmakeourcodemorefluentandfunctional;nowit'stimetolearnsomeofthesefunctions:

$scala



scala>//Createsthenumbers1,2,3,4,5andthemmultiplytheyby2and

createsanewVector

scala>println((1to5).map(_*2))

Vector(2,4,6,8,10)

scala>

scala>//Creates1,2,3andsumthemallwitheachorherandreturnthetotal

scala>println((1to3).reduceLeft(_+_))

6

scala>

scala>//Creates1,2,3andmultiplyeachnumberbyitselfandreturna

Vector

scala>println((1to3).map(x=>x*x))

Vector(1,4,9)

scala>

scala>//Createsnumbers1,2,3,4ans5filteronlyOddnumbersthemmultiply

themoddsby2andreturnaVector

scala>println((1to5)filter{_%2==0}map{_*2})

Vector(4,8)

scala>

scala>//CreatesaListwith1to5andthemprinteachelementbeing

multiplyedby2

scala>List(1,2,3,4,5).foreach((i:Int)=>println(i*2))

2

4

6

8

10

scala>

scala>//CreatesaListwith1to5andthenprinteachelementbeing

multipliedby2

scala>List(1,2,3,4,5).foreach(i=>println(i*2))

2

4

6

8

10

scala>

scala>//Drops3elementsfromthelists

scala>println(List(2,3,4,5,6).drop(3))

List(5,6)

scala>println(List(2,3,4,5,6)drop3)

List(5,6)

scala>

scala>//Zip2listsintoasingleone:Itwilltake1elementofeachlist

andcreateapairList

scala>println(List(1,2,3,4).zip(List(6,7,8)))

List((1,6),(2,7),(3,8))

scala>

scala>//Takenestedlistsandcreateasinglelistwithflatelements

scala>println(List(List(1,2),List(3,4)).flatten)

List(1,2,3,4)

scala>

scala>//FindsapersoninaListbyAge

scala>caseclassPerson(age:Int,name:String)

definedclassPerson

scala>println(List(Person(31,"Diego"),Person(40,"Nilseu")).find((p:Person)

=>p.age<=33))

Some(Person(31,Diego))

scala>

PartialapplicationInScala,theunderscore(_)meansdifferentthingsindifferentcontexts.Theunderscorecanbeusedtopartiallyapplyafunction.Itmeansavaluewillbesuppliedlater.Thisfeatureisusefulforfunctioncompositionandallowsyoutoreusefunctions.Let'sseesomecode.

PartialfunctioninScalaREPLFollowingisanexampleusingPartialfunctioninScalaREPL:

$scala



scala>defsum(a:Int,b:Int)=a+b

sum:(a:Int,b:Int)Int

scala>

scala>valadd6=sum(6,_:Int)

add6:Int=>Int=<function1>

scala>

scala>println(add6(1))

7

scala>

Intheprecedingcode,first,wedefineafunctioncalledsum,whichtakestwoIntparametersandcalculatesasumofthesetwoparameters.Later,wedefineafunctionandholditasavariablecalledadd6.Fortheadd6functiondefinition,wejustcallthesumfunctionpassing6and_.Scalawillgettheparameterpassedthroughadd6,andpassitthroughthesumfunction.

CurriedfunctionsThisfeatureisverypopularinfunctionlanguageslikeHaskell.Curriedfunctionsaresimilartopartialapplications,becausetheyallowsomeargumentstopassnowandotherslater.However,theyarealittlebitdifferent.

Curriedfunctions-ScalaREPLFollowingisanexampleusingcurriedfunctioninScalaREPL:

$scala



scala>//FunctionDefinition

scala>defsum(x:Int)(y:Int):Int=x+y

sum:(x:Int)(y:Int)Int

scala>

scala>//Functioncall-Callingacurriedfunction

scala>sum(2)(3)

res0:Int=5

scala>

scala>//DoingpartialwithCurriedfunctions

scala>valadd3=sum(3)_


scala>

scala>//Supplythelastargumentnow

scala>add3(3)

res1:Int=6

scala>

Fortheprecedingcode,wecreateacurriedfunctioninthefunctiondefinition.Scalaallowsustotransformregular/normalfunctionsintocurriedfunctions.Thefollowingcodeshowstheusageofthecurriedfunction.

CurriedtransformationinScalaREPLFollowingisanexampleusingcurriedtransformationinScalaREPL:

$scala



scala>defnormalSum(x:Int,y:Int):Int=x+y

normalSum:(x:Int,y:Int)Int

scala>

scala>valcurriedSum=(normalSum_).curried

curriedSum:Int=>(Int=>Int)=<function1>

scala>

scala>valadd3=curriedSum(3)


scala>

scala>println(add3(3))

6

scala>

OperatoroverloadingLikeC++,Scalapermitsoperatoroverload.ThisfeatureisgreatforcreatingcustomDomainSpecificLanguages(DSL),whichcanbeusefultocreatebettersoftwareabstractionsoreveninternalorexternalAPIsfordevelopers,orforbusinesspeople.Youshouldusethisfeaturewithwisdom--imagineifallframeworksdecidetooverloadthesameoperatorswithimplicits!Youmightrunintotrouble.ScalaisaveryflexiblelanguagecomparedtoJava.However,youneedtobecareful,otherwiseyoucouldcreatecodethat'shardtomaintainorevenincompatiblewithotherScalaapplications,libraries,orfunctions.

ScalaoperatoroverloadinginScalaREPLFollowingisanexampleusingScalaoperatoroverloadinginScalaREPL:

$scala



scala>caseclassMyNumber(value:Int){

|def+(that:MyNumber):MyNumber=newMyNumber(that.value+this.value)

|def+(that:Int):MyNumber=newMyNumber(that+this.value)

|}

definedclassMyNumber

scala>valv=newMyNumber(5)

v:MyNumber=MyNumber(5)

scala>

scala>println(v)

MyNumber(5)

scala>println(v+v)

MyNumber(10)

scala>println(v+newMyNumber(4))

MyNumber(9)

scala>println(v+8)

MyNumber(13)

scala>

Asyoucansee,wehavetwofunctionscalled+.OneofthisfunctionsreceivesaMyNumbercaseclass,andtheotherreceivesaIntvalue.YoucanuseOOinScalawithregularclassesandfunctionsaswellifyouwish.We'realsofavoringimmutabilityherebecausewealwayscreateanewinstanceofMyNumberwhentheoperation+happens.

ImplicitsImplicitsallowyoutodomagicinScala.Withgreatpowercomesgreatresponsibility.ImplicitsallowtoyoucreateverypowerfulDSL,buttheyalsoallowyoutogetcrazy,sodoitwithwisdom.Youareallowedtohaveimplicitfunctions,classes,andobjects.TheScalalanguageandothercoreframeworksfromtheScalaecosystemlikeAkkaandPlayFrameworkuseimplicitsmanytimes.

ScalaImplicitsinSCALAREPL$scala



scala>implicitdeftransformStringtoInt(n:String)=n.toInt

warning:therewasonefeaturewarning;re-runwith-featurefordetails

transformStringtoInt:(n:String)Int

scala>

scala>vals:String="123456"

s:String=123456

scala>println(s)

123456

scala>

scala>vali:Int=s

i:Int=123456

scala>println(i)

123456

scala>

Touseimplicits,youneedtousethekeywordimplicitbeforeafunction.Scalawillimplicitlycallthatfunctionwhenitisappropriate.Forthiscase,itwillcalltoconverttheStringtypetoInttypeaswecansee.

ImplicitParameteratScalaREPL$scala



scala>implicitvalyValue:Int=6

yValue:Int=6

scala>defsum(x:Int)(implicityValue:Int)=x+yValue

sum:(x:Int)(implicityValue:Int)Int

scala>valresult=sum(10)

result:Int=16

scala>println(result)

16

scala>

Forthisothercase,giveninthelastcode,weuseanimplicitparameterinthefunctionsum.Wealsousedacurriedfunctionhere.Wedefinedtheimplicitfunctionfirst,andthencalledthesumfunction.Thistechniqueisgoodforexternalizedfunctionsconfigurationandvaluesyouwouldletithardcode.Italsosaveslinesofcode,becauseyoudon'tneedtopassaparametertoallfunctionsallthetime,soit'squitehandy.

FuturesFuturesenableanefficientwaytowriteparalleloperationsinanonblockingIOfashion.Futuresareplaceholderobjectsforvaluesthatmightnotexistyet.Futuresarecomposable,andtheyworkwithcallbacksinsteadoftraditionalblockingcode.

SimpleFuturecodeinScalaREPL$scala



scala>importconcurrent.Future

importconcurrent.Future

scala>importconcurrent.ExecutionContext.Implicits.global

importconcurrent.ExecutionContext.Implicits.global

scala>

scala>valf:Future[String]=Future{"Helloworld!"}

f:scala.concurrent.Future[String]=Success(Helloworld!)

scala>

scala>println("Result:"+f.value.get.get)

Result:Helloworld!

scala>

scala>println("Result:"+f)

Result:Success(Helloworld!)

scala>

InordertoworkwithfuturesinScala,wehavetoimportconcurrent.Future.Wealsoneedanexecutor,whichisawaytoworkwiththreads.Scalahasadefaultsetofexecutionservices.Youcantweakitifyoulike,however,fornowwecanjustusethedefaults;todothat,wejustimportconcurrent.ExecutionContext.Implicits.global.

It'spossibletoretrievetheFuturevalue.ScalahasaveryexplicitAPI,whichmakesthedeveloper'slifeeasier,andalsogivesgoodsamplesforhowweshouldcodeourownAPIs.Futurehasamethodcalledvalue,whichreturnsOption[scala.util.Try[A]]whereAisthegenerictypeyouareusingforthefuture;forourcase,it'saStringA.Tryisadifferentwaytodoatry...catch,andthisissafer,becausethecallerknowsbeforehandthatthecodetheyarecallingmayfail.Try[Optional]meansthatScalawilltrytorunsomecodeandthecodemayfail--evenifitdoesnotfail,youmightreceiveNoneorSome.Thistypeofsystemmakeseverybody'slivesbetter,becauseyoucanhaveSomeorNoneastheOptionreturn.Futuresareakindofcallback.Forourprevioussamplecode,theresultwasobtainedquitequickly,however,weoftenusefuturestocallexternalAPIs,RESTservices,Microservices,SOAPWebservices,oranycodethattakestimetorunandmightnotgetcompleted.FuturesalsoworkwithPatternMatcher.Let'sseeanothersamplecode.

AcompleteFuturesampleatScalaREPL$scala



scala>importconcurrent.Future

importconcurrent.Future

scala>importconcurrent.ExecutionContext.Implicits.global

importconcurrent.ExecutionContext.Implicits.global

scala>importscala.util.{Success,Failure}

importscala.util.{Success,Failure}

scala>defcreateFuture():Future[Int]={

|Future{

|valr=scala.util.Random

|if(r.nextInt(100)%2==0)0elsethrownewRuntimeException("ODDnumbers

arenotgoodhere:(")

|}

|}

createFuture:()scala.concurrent.Future[Int]

scala>defevaluateFuture(f:Future[_]){

|f.onComplete{

|caseSuccess(i)=>println(s"ASuccess$i")

|caseFailure(e)=>println(s"Somethingwentwrong.Ex:

${e.getMessage}")

|}

|}

evaluateFuture:(f:scala.concurrent.Future[_])Unit

scala>evaluateFuture(createFuture)

scala>Somethingwentwrong.Ex:ODDnumbersarenotgoodhere:(

evaluateFuture(createFuture)

ASuccess0


Somethingwentwrong.Ex:ODDnumbersarenotgoodhere:(


Somethingwentwrong.Ex:ODDnumbersarenotgoodhere:(


ASuccess0


ASuccess0

scala>

ThereisafunctioncalledcreateFuture,whichcreatesFuture[Int]eachtimeyoucallit.Intheprecedingcode,weusescala.util.Randomtogeneraterandomnumbersbetween0and99.Ifthenumberiseven,wereturna0,whichmeanssuccess.However,ifthenumberisodd,wereturnaRuntimeException,whichwillmeanafailure.

ThereisasecondfunctioncalledevaluateFuture,whichreceivesanyFuture.Weallowaresultofanykindofgenericparameterizedtypeoffunction,becauseweusedthemagicunderscore_.ThenweapplyPatternMatcherwithtwocaseclasses:SuccessandFailure.Inboththecases,wejustprintonstdin.WealsouseanotherinterestingandhandyScalafeaturecalledStringinterpolation.WeneedtowestarttheStringwithsbefore"".Thisallowsustouseexpressionswith$and${}toevaluateanyvariableinthecontext.Thisisadifferent

approachforStringconcatenationfromwhatwehavedonesofar.Later,wemade6callsfortheevaluteFuturefunction,passinganewFutureeachtime,createdbythefunctioncreateFuture.

ReactiveProgramingandRxScalaReactiveprogrammingisbetter,scalable,andafasterwaytobuildapplications.ReactiveProgramingcanbedonewithOOlanguages,however,theymakealotofsensewithFPlanguages.WhenFPismarriedtoReactivePrograming,wegetsomethingcalledFunctionalReactivePrograming(FRP).ScalaFRPcanbeusedformanypurposeslikeGUI,Robotics,andMusic,becauseitgivesyouabettermodeltomodeltime.Reactiveprogrammingisanewtechnique,whichworkswithStreams(alsoknownasDataFlows).Streamsisawaytothinkandcodeapplicationsinawaywhichcanexpressdatatransformationsandflow.Themainideaistopropagatechangesthroughacircuitorflow.Yes,wearetalkingaboutanewwaytodoasyncprogramming.

ThemainlibraryforReactiveProgramingiscalledReactiveExtensions(Rx)-http://reactivex.io/),originallybuiltfor.NETbyEricMeijer.ItcombinesthebestideasfromtheObserverandIteratorPatterns,andFP.RxhasimplementationsformanylanguageslikeScala,Java,Python,.NET,PHP,andothers(https://github.com/ReactiveX).CodingwithRxiseasy,andyoucancreateStreams,combinewithquery-likeoperators,andalsolisten(subscribe)toanyobservableStreamstoperformdatatransformations.RxisusedbymanysuccessfulcompaniestodaylikeNetflix,GitHub,Microsoft,SoundCloud,Couchbase,Airbnb,Trello,andseveralothers.Inthisbook,wewilluseRxScala,whichistheScalaimplementationoftheReactiveStreams.

Thefollowingtableshowsthemainclass/conceptsyouneedtoknowinordertoworkwithRx.

Term/Class Concept

Observable CreateasynccomposableStreamsfromsources.

Observer Acallbackfunctiontype.

Subscription TheboundbetweentheSubscriberandtheObservable.ReceivesnotificationsfromObservables.

ReactiveStreamsisalsothenameofacommonspecificationtryingtoconsolidateandstandardizethereactivestreamprocessing,ThereareseveralimplementationssuchasRxJava/RxScala,Reactor,Akka,Slick,andVert.x.Youcanfindmoreathttps://github.com/reactive-streams/reactive-streams-jvm.

BacktotheObservables--wecanperformallkindsofoperationswithobservables.For

http://reactivex.io/

https://github.com/ReactiveX

https://github.com/reactive-streams/reactive-streams-jvm

instance,wecanfilter,select,aggregate,compose,performtime-basedoperations,andapplybackpressure.TherearetwobigwinswithObservablesinsteadofcallbacks.Firstofall,Observablesarenotopinionatedabouthowlow-levelI/Oandthreadinghappens,andsecondly,whenyouaredoingcomplexcode,callbackstendtobenested,andthatiswhenthingsgetuglyandhardtoread.ObservableshaveasimplewaytodocompositionthankstoFP.

Observablespushvaluestoconsumerswhenevervaluesareavailable,whichisgreatbecausethenthevaluescanarriveinsyncorasyncfashion.Rxprovidesaseriesofcollectionoperatorstodoallsortsofdatatransformationsyoumayneed.Let'sseesomecodenow.WewilluseRxScalaversion0.26.1,whichiscompatiblewithRxJavaversion1.1.1+.RxScalaisjustawrapperforRxJava(CreatedbyNetflix).WhynotuseRxJavastraight?Becausethesyntaxwon'tbepleasant;withRxScala,wecanhaveafluentScalaexperience.RxJavaisgreat,however,Javasyntaxforthisisnotpleasant-asScalais,infact,prettyugly.

SimpleObservablesScalawithRxScalapackagescalabook.rx.chap1

importrx.lang.scala.Observable

importscala.concurrent.duration._

objectSimpleRXextendsApp{

valo=Observable.

interval(100millis).

take(5)

o.subscribe(x=>println(s"Gotit:$x"))

Thread.sleep(1000)

Observable.

just(1,2,3,4).

reduce(_+_).

subscribe(r=>println(s"Sum1,2,3,4is$rinaRxWay"))

}

IfyourunthisprecedingScalaprogram,youwillseethefollowingoutput:

SimpleObservablesScalawithRxScala-ExecutionintheconsoleGotit:0

Gotit:1

Gotit:2

Gotit:3

Gotit:4

Sum1,2,3,4is10inaRxWay

IfyoutrytorunthiscodeintheScalaREPL,itwillfail,becauseweneedtheRxScalaandRxJavadependencies.Forthis,wewillneedSBTanddependencymanagement.Donotworry,wewillcoverhowtoworkwithSBTinourScalaapplicationinthenextchapter.

Goingbacktotheobservables,weneedtoimporttheScalaObservable.MakesureyougetitfromtheScalapackage,becauseifyougettheJavaone,youwillhaveissues:intheveryfirstpartofthecode,wewillgetnumbersstartingfrom0each100milliseconds,andthiscodewouldrunforever.Toavoidthis,weusethetakefunctiontoputalimitintothecollection,sowewillgetthefirstfivevalues.Then,later,wesubscribetotheobserver,andwhendataisready,ourcodewillrun.Forthefirstsample,it'sprettyeasy,wearejustprintingthevalueswehavegot.Thereisathreadsleepinthisprogram,otherwise,theprogramwouldterminate,andyouwouldnotseeanyvalueontheconsole.

Thesecondpartofthecodedoessomethingmoreinteresting.Firstofall,itcreatesanObservablefromastaticlistofvalues,whichare1,2,3,and4.Weapplyareducefunctionintotheelements,whichwillsumalltheelementswitheachother,andthenwesubscribeandprinttheresult.

ComplexScalawithRxScalaObservablespackagescalabook.rx.chap1

importrx.lang.scala.Observable

objectComplexRxScalaextendsApp{

Observable.

just(1,2,3,4,5,6,7,8,9,10).//1,2,3,4,5,6,7,8,9,10

filter(x=>x%2==0).//2,4,6,8,10

take(2).//2,4

reduce(_+_).//6

subscribe(r=>println(s"#1$r"))

valo1=Observable.

just(1,2,3,4,5,6,7,8,9,10).//1,2,3,4,5,6,7,8,9,10

filter(x=>x%2==0).//2,4,6,8,10

take(3).//2,4,6

map(n=>n*n)//4,16,36

valo2=Observable.

just(1,2,3,4,5,6,7,8,9,10).//1,2,3,4,5,6,7,8,9,10

filter(x=>x%2!=0).//1,3,5,7,9

take(3).//1,3,5

map(n=>n*n)//1,9,25

valo3=o1.

merge(o2).//2,16,36,1,9,25

subscribe(r=>println(s"#2$r"))

}

TheprecedingfirstpartofthecodecreatesanObservablewithnumbersfrom1to10,andthenappliesafilterfunction,whichwillgetonlytheevennumbers.Itthenreducesthem,calculatestheirsum,andlastly,printsthesolution.Youcanvisualizeitasdepictedinthefollowingimage:

Forthesecondpartofthecode,wecreatetwodifferentobservables.Thefirstoneiswithevennumbersandthesecondoneiswithoddnumbers.Thesetwoobservablesaredecoupledfromeachother;youcancontrolasmanyobservablesyouwant.Lateron,thecodeusesamergefunctiontojointhesetwoobservablesintoathirdandnewobservablecontainingthecontentofthefirstandsecondobservables.

Merging2Observables

Therearemanyfunctionsandoptions,andyoucanseethewholelistathttp://rxmarbles.com/andhttps://github.com/ReactiveX/RxScala.Forthesakeofsimplicity,fornow,wearejustworkingwithnumbers.Later,wewillusethistodomoreadvancecompositionsincludingdatabasecallsandexternalwebservicescalls.

http://rxmarbles.com/

https://github.com/ReactiveX/RxScala

SummaryInthischapter,welearnedthebasicconceptsofFP,ReactivePrograming,andtheScalalanguage.WelearnedaboutthebasicconstructsoftheScalalanguageandFunctionalProgramming,functions,collections,andOOinScala,andconcurrentprogrammingwithFutures.

Next,wewillseehowtouseSBTtobuildScalaprojects.WewilllearnhowtocompileandrunScalaapplicationsusingSBT.

Chapter2.CreatingYourAppArchitectureandBootstrappingwithSBTInthepreviouschapter,welearnedaboutFunctionalProgramingandScala.ThischapterwillbefocusedonSimpleBuildTool(SBT)andActivatorinordertoBootstrapcomplexScalaandPlayframeworkprojects.UsingSBTandActivator,wecanperformseveraldevelopmenttaskssuchasbuilding,runningtests,anddeployingtheapplication(whichwillbecoveredindetailinChapter10,ScalingUp).Let'sgetstarted.

Inthischapter,wewillseethefollowingtopics:

SBTbasics--installation,structure,anddependenciesActivatorbasics--creatingprojectsOverallarchitectureofourapplication

IntroducingSBTSBTistheultimateScalasolutionforbuildingandpackingScalaapplications.SBThaslotsofplugins,suchasEclipseandIntelliJIDEAprojectsgeneration,whichhelpagreatdealwhenwearedoingScaladevelopment.SBTisbuiltinScalainordertohelpyoubuildyourScalaapplications.However,SBTcanstillbeusedtobuildJavaapplicationsifyouwish.

ThecorefeaturesofSBTareasfollows:

Scala-basedbuilddefinitionIncrementalcompilationContinuouscompilationandtestingGreatsupportfortestinglibrariessuchasScalaCheck,Specs,ScalaTest,andJUnitREPLintegrationParallelTaskexecution

WewilluseSBTwiththeTypesafeActivatortoBootstrapourapplicationlaterinthisverychapter.Beforedoingso,wewillplaywithSBTtolearnthekeyconceptsofsettingupabuildprojectforaScalaapplication.Inthisbook,wewillbeusingSBTversion0.13.11.

InstallingSBTonUbuntuLinuxKeepinmindthatweneedtohaveJavaandScalainstalledbeforeinstallingSBT.Ifyoudon'thaveJavaandScalainstalled,gobacktoChapter1,IntroductiontoFP,Reactive,andScalaandfollowtheinstallationinstructions.Openaterminalwindow,andrunthefollowingcommandsinordertodownloadandinstallSBT:

$cd/tmp

$wgethttps://repo.typesafe.com/typesafe/ivy-releases/org.scala-

sbt/sbt-launch/0.13.11/sbt-launch.jar?

_ga=1.44294116.1153786209.1462636319-Osbt-launch.jar

$chmod+xsbt-launch.jar

$mkdir~/bin/&&mkdir~/bin/sbt/

$mvsbt-launch.jar~/bin/sbt/

$cd~/bin/sbt/

$touchsbt

Addthefollowingcontenttothe~/bin/sbt/sbtfile:

#!/bin/bash

w

Aftersavingthe~/bin/sbt/sbtfile,weneedtogivepermissiontoexecutethefilewiththefollowingcommand:

$chmodu+x~/bin/sbt/sbt

NowweneedtoputSBTintotheoperationalsystempathinordertobeabletoexecuteanywhereintheLinuxterminal.WeneedtoexportSBTthroughthePATHcommandintothe~/.bashrcfile.Openthe~/.bashrcfileinyourfavoriteeditor,andaddthefollowingcontent:

exportSBT_HOME=~/bin/sbt/

exportPATH=$PATH:$SBT_HOME

Weneedtosourcethefileusing$source~/.bashrc.

NowwecanrunSBTandmoveonwiththeinstallation.Whenyounowtype$sbtonyourconsole,SBTwilldownloadallthedependenciesrequiredforusetorunitself.

GettingstartedwithSBTLet'screatefoldernamedhello-world-sbt,andaddthefollowingprojectstructure:

Forbuild.properties,youneedtohavethefollowingcontent:

build.properties

sbt.version=0.13.11

Forhello_world.scala,wewillusethefollowingcode:

hello_world.scala

objectSbtScalaMainAppextendsApp{

println("HelloworldSBT/ScalaApp")

}

FornowwewilluseanSBTDSL.However,sinceSBTiswrittenScala,wecanusethebuild.scalaformatifwewish.Thisishandyinsomecases,becausewecanuseanykindofScalacodeinordertomakethebuildmoredynamicandtoreusecodeandtasks.

Wewillsetsomepredefinedvariables,however,youcancreateyourownvariables,whichcanbeusedtoavoidduplicatecode.Finally,let'sseethebuild.sbtfilecontentasfollows:

build.scala

name:="hello-world-sbt"

version:="1.0"

scalaVersion:="2.11.8"

scalaVersioninThisBuild:="2.11.8"

Intheprecedingcode,wehavethenameoftheapplication,theversionwhichwillbeusedinthegeneratedJARfile,andalsotheScalaversionusedontheapplicationandtheoneusedinthebuildprocess.Wearereadytobuildthisproject,soopenyourterminalandtype$sbtcompile.

ThisinstructionwillmakeSBTcompileourScalacode,andyoushouldseesomethinglikethisfollowingscreen:

$sbtcompile

Congratulations!SBTjustcompiledourScalaapplication.NowwecanruntheapplicationusingSBT.Inordertodothis,wejustneedtotype$sbtrunasfollows:

$sbtrun

SBTmakesiteasiertotestandplaywithyourScalaapplication,becauseSBThasaREPLliketheScalaREPLwewereplayingwithinChapter1,IntroductiontoFP,Reactive,andScala.TheSBTREPLmakesalltheScalacodethatyoumighthaveundertheprojectavailableattheREPL.

Executethecommand$sbtconsole.

OnceyouareintotheREPL,youcantypeanyScalacode.Asyoumust'verealized,IjustcalledthemainScalaapplicationdirectlyvia$SbtScalaMainApp.main(null).

AddingdependenciesLikeanybuildtool,SBTallowsyoutoresolvedependencies.SBTusestheIvy/Maven2patternstoresolvedependencies.So,ifyouarefamiliarwithMaven2,Gradle,orAnt/Ivy,youwillrealizethatsettingSBTdependenciesisthesame,althoughwithadifferentsyntax.Dependenciesaredefinedinthebuild.sbtfile.ThereisnoScaladevelopmentwithoutunittests.OneofthemostpopulartestinglibrariesisJUnit(http://junit.org/junit4/).JUnitworkswithJavaandScalaprojects.SBTwilldownloadandaddJUnittoyourScalaapplicationclasspathparameter.Weneedtoeditthebuild.sbtfiletoaddJUnitasadependencyasfollows:

build.sbt

name:="hello-world-sbt"

version:="1.0"



libraryDependencies+="junit"%"junit"%"4.12"%Test

libraryDependencies+="com.novocode"%"junit-interface"%"0.11"

%"test"

testOptions+=Tests.Argument(TestFrameworks.JUnit,"-q","-v")

AsImentionedbefore,SBTusesthesamepatternasMaven2/Ivywith:groupID+artifactid+version.Ifyoudon'tknowthepatternforthelibraryyouwanttoadd,youcancheckouttheMavenRepositorywebsite(theygenerateSBTconfigsaswell)atthefollowinglink:http://mvnrepository.com/artifact/junit/junit/4.12.

http://junit.org/junit4/

http://mvnrepository.com/artifact/junit/junit/4.12

SBThasscopefordependencies.Wedon'twanttoshipJUnitaspartofthesourcecodedependency.That'swhywehavethe%Testafterthedependencydefinition.

Onceyouhavesavedthefilewiththenewcontent,youcanrun$sbtcompile.SBTwilldownloadJUnitforyouandstorethejarintothelocalIvyrepofileslocatedat/home/YOUR_USER/.ivy2/cache.Withthedependencyinplace,wecanaddmorecodeandalsouseSBTtorunourtestsasfollows:

src/main/scala/calc.scala

classCalculator{

defsum(a:Int,b:Int):Int={

returna+b

}

defmultiply(a:Int,b:Int):Int={

returna*b

}

}

Intheprecedingcode,wejustcreatedasimpleandstraightforwardcalculatorinScala,whichcanaddtwointegernumbersandalsoperformmultiplicationoftwointegersnumbers.NowwecanmoveontotheunittestsusingJUnit.Testsneedtobelocatedinthesrc/test/scala/folder.Lookatthefollowingcode:

src/test/scala/calcTest.scala

importorg.junit.Test

importorg.junit.Assert._

classCalcTest{

@Test

deftestSumOK():Unit={

valc:Calculator=newCalculator()

valresult:Int=c.sum(1,5)

assertNotNull(c)

assertEquals(6,result)

}

@Test

deftestSum0():Unit={


valresult:Int=c.sum(0,0)

assertNotNull(c)


}

@Test

deftestMultiplyOk():Unit={


valresult:Int=c.multiply(2,3)

assertNotNull(c)


}

@Test

deftestMultiply0():Unit={



assertNotNull(c)


}

}

Okay,nowwecanjustrunthetestswiththecommand$sbttestasfollows:

Asyoucanseeinthepreviousscreenshot,allthetestsarerunning.AtestiscreatedwhenweaddtheJavaannotation@Test,anditneedstobeapublicfunctionaswell.Thereisonetest,

calledtestMultiply0,whichfails,becauseitexpectstheresult4,but5multipliedby0iszero,sothetestiswrong.Let'sfixthismethodbychangingassertiontoacceptzero,likeinthefollowingcode,andrerunthe$sbttestasfollows:

@Test

deftestMultiply0():Unit={



assertNotNull(c)


}

$sbttestgivesyouthefollowingresult:

Hooray!Allthetestspassed.Bydefault,SBTrunsallyourtestsinparallel,whichisgreatforspeedingupbuildtime-nobodylikestowaitwhendoingbuilds,andScalaisnotthefastesttechtobuild.However,youcandisableparalleltestsifyouwantbyaddingthefollowinglineintothebuild.sbt:

parallelExecutioninTest:=false

GeneratingEclipseprojectfilesfromSBTSBTviapluginscangenerateEclipsefiles.It'spossibletoaddthesepluginsdirectlyintoyourbuild.sbtfile.However,thereisabettersolution.Youcandefineglobalconfigurations,whichareideal,becauseyoudon'tneedtoaddineverysimplebuild.sbtfileyouhave.Thisalsomakesalotofsenseifyouareworkingwithmultipleprojectsand/oryouareworkingwithopensourceprojectsbecause,asitisamatterofpreference,peopleoftendonotversionateIDEfiles.

Gotothefollowingdirectoryifitexists,otherwisepleasecreatethefollowingdirectory:/home/YOUR_USER/.sbt/0.13/plugins.

Nowcreatethefilebuild.sbtwiththefollowingcontent:

/home/YOUR_USER/.sbt/0.13/plugins/build.sbtGlobalconfigfile

resolvers+=Classpaths.typesafeResolver

addSbtPlugin("com.typesafe.sbteclipse"%"sbteclipse-plugin"%

"4.0.0")

Onceyousavethefilewiththiscontent,wecanreloadourSBTapplicationbyexecuting$sbtreload,orquittheSBTconsole(Ctrl+D)andopensbtagainusing$sbt.

$sbtreload

NowwecangenerateEclipsefilesbyusingthecommand$eclipse.

Oncethegenerationisdone,youcanimportthe.projectfilegeneratedintoEclipse.

Bydefault,EclipsedoesnotattachsourcefolderswhengeneratingtheEclipseproject.Ifyouwantthesourcecode(ofthird-partydepslikeJunit),youneedtoaddanextralineintoyourbuild.sbtproject.Addingsourcefoldersisoftenagoodidea,otherwise,youcan'tdoproperdebuggingwithoutthesourcecode.

build.sbt

EclipseKeys.withSource:=true

TheSBTScalaapplicationimportedintoEclipseisshowninthefollowingscreenshot:

ApplicationdistributionForthissection,wewillplaywiththreedifferentpackagingsolutions,whichareasfollows:

ThedefaultSBTpackagersSBTassemblypluginSBTnativepackager

SBTcangeneratejarsbydefault.ItisalsopossibletogenerateRPMs,DEBs,andevendockerimagesviaSBTplugins.Firstofall,let'sgenerateanexecutablejar.ThisisdonebythetaskpackageinSBT.OpenyourSBTconsole,andrunthe$sbtpackage.However,wewanttogenerateaFATjar,whichisajarwithallotherdependencies(jars)oftheapplication.Inordertodothat,weneedtouseanotherplugincalledassembly.

TheSBTpackagecangenerateajar,butitdoesnotshipthedependencies.Inordertousetheassemblyplugin,createthefileproject/assembly.sbt,andaddthecontentasfollows:

$project/assembly.sbt

addSbtPlugin("com.eed3si9n"%"sbt-assembly"%"0.11.2")

Inourbuild.sbt,weneedtoimporttheassemblyplugin,likethis:

$build.sbt(putintothetopofthefile)

importAssemblyKeys._

assemblySettings

Nowwecanrun$sbtassemblytogenerateourFATjar.

Therewego.NowwecanrunthisasanormalJavaapplicationjustusingthecommandjava-jarasfollows:

$java-jarhello-world-sbt/target/scala-2.11/hello-world-sbt-

assembly-1.0.jar

HelloworldSBT/ScalaAppThereisanotherusefulpluginforpackingtheScalaapplication,whichissbt-native-packager.sbt-native-packagercangeneratepackagesforLinuxOSlikeDEBandRPMfiles.Sincethisisanewplugin,weneedtocreateafilecalledplugins.sbtinproject/asfollows:

resolvers+="Typesaferepository"at

"http://repo.typesafe.com/typesafe/releases/"

addSbtPlugin("com.typesafe.sbt"%%"sbt-native-packager"%"1.0.4")

Attheveryendofyourbuild.sbt,youneedtoaddthisline:

enablePlugins(JavaAppPackaging)

Nowwecangeneratepackageswithsbt-native-packagerusing$sbtuniversal:packageBinor$sbtuniversal:packageZipTarball.

NowwehaveaZIPandaTGZfilewithyourapplicationinthefolderhello-world-sbt/target/universal/.InsidethisZIP/TGZfile,wehaveourapplicationinajarformatwithallthedependencies;fornowwejusthaveScala,butifwehadmore,theywouldbethereaswell.ThereareSHandBATscriptstorunthisapplicationeasilyinLinux(SH)andWindows(BAT)respectively.

sbt-native-packagercanalsocookdockerimages.Thisisgreat,becausethatmakesiteasiertodeployapplicationsintoproductionenvironments.Ourprojectisfullyreadytobakedockerimages.WeneedtohavedockerinstalledonLinux;youcandosobyrunningthefollowingcommands:

sudoapt-getupdate

sudoapt-getinstalldocker-engine

sudoservicedockerstart

sudodockerrunhello-world

Youshouldseesomethinglikethefollowingscreenshotifyou'vesuccessfullyinstalledDocker:

Nowyoucanrun$sbt,andthengenerateyourdockerimagesbyusingthecommand$docker:publishLocal.Youwillseeanoutputsimilartothefollowing:

>docker:publishLocal

[info]Wrote

/home/diego/github/diegopacheco/Book_Building_Reactive_Functional_Scala_Applic

ations/hello-world-sbt/target/scala-2.11/hello-world-sbt_2.11-1.0.pom

[info]SendingbuildcontexttoDockerdaemon5.769MB

[info]Step1:FROMjava:latest

[info]Pullingrepositorydocker.io/library/java

[info]31ae46664586:Pullingimage(latest)fromdocker.io/library/java

[info]31ae46664586:Pullingimage(latest)fromdocker.io/library/java,

endpoint:https://registry-1.docker.io/v1/

[info]31ae46664586:Pullingdependentlayers

[info]e9fa146e2b2b:Pullingmetadata

[info]Status:Downloadednewerimageforjava:latest

[info]docker.io/library/java:thisimagewaspulledfromalegacyregistry.

Important:Thisregistryversionwillnotbesupportedinfutureversionsof

docker.

[info]--->31ae46664586

[info]Step2:WORKDIR/opt/docker

[info]--->Runningin74c3e354e9fd

[info]--->d67542bcaa1c

[info]Removingintermediatecontainer74c3e354e9fd

[info]Step3:ADDopt/opt

[info]--->f6cec2a2779f

[info]Removingintermediatecontainer0180e167ae2d

[info]Step4:RUNchown-Rdaemon:daemon.

[info]--->Runningin837ecff2ffcc

[info]--->8a261bd9d88a

[info]Removingintermediatecontainer837ecff2ffcc

[info]Step5:USERdaemon

[info]--->Runningin6101bd5b482b

[info]--->e03f5fa23bdf

[info]Removingintermediatecontainer6101bd5b482b

[info]Step6:ENTRYPOINTbin/hello-world-sbt

[info]--->Runningin43de9335129c

[info]--->eb3961f1e26b

[info]Removingintermediatecontainer43de9335129c

[info]Step7:CMD

[info]--->Runningin302e1fcd0a3d

[info]--->04e7872e85fa

[info]Removingintermediatecontainer302e1fcd0a3d

[info]Successfullybuilt04e7872e85fa

[info]Builtimagehello-world-sbt:1.0

[success]Totaltime:447s,completed07/05/201617:41:47

>

Youcanconfirmthatthereisanewdockerimageinyoursystemjustbyrunningthecommand$dockerps:

Theveryfirstimageisourdockerimagegeneratedbythesbt-native-packagerpluginwithourScalaapplication.Congratulations!YouhaveadockercontainerrunningwithyourScalaapplication.SBTNativePackagerisreallypowerful,yetsimpletouse.Youcangetmoredetailsontheofficialdocumentationsite(http://www.scala-sbt.org/sbt-native-packager/gettingstarted.html).

ThesearethebasicthingsweneedtoknowaboutSBTtobuildprofessionalScalaapplications.SBThasmanyotherfeaturesandpossibilities,whichyoucancheckitoutathttp://www.scala-sbt.org/0.13/docs/index.html.Next,wewilllearnaboutTypesafeActivator,whichisawrapperaroundSBTthatmakesiteasytousewithPlayframeworkapplications.

http://www.scala-sbt.org/sbt-native-packager/gettingstarted.html

http://www.scala-sbt.org/0.13/docs/index.html

BootstrappingourPlayframeworkappwithActivatorLightband(formerTypesafe)hasanothertoolcalledActivator(https://www.lightbend.com/community/core-tools/activator-and-sbt),whichisawrapperontopofSBT.ActivatormakesiteasiertocreateReactiveapplicationsusingScala,Akka,andthePlayframework.Don'tworryaboutthePlayframeworkrightnow,becausewewillcoverthatingreaterdetailinChapter3,DevelopingtheUIwithPlayFramework.AkkawillbecoveredindetailinChapter8,DevelopingachatwithAkka.

Let'sdownloadandinstallActivator,andBootstrapourarchitecture.Remember,weneedtohaveJava8andScala2.11alreadyinstalled.Ifyoudon'thaveJava8orScala2.11,gobacktoChapter1,IntroductiontoFP,Reactive,andScalaandinstallthem.

Firstofall,youneedtodownloadactivatorfromhere:https://www.lightbend.com/activator/download

Irecommendthatyoudownloadtheminimalpackage,andletActivatordownloadandinstalltherestoftheotherdependenciesforyou.Youcandownloadtheminimalpackagehere:https://downloads.typesafe.com/typesafe-activator/1.3.10/typesafe-activator-1.3.10-minimal.zip.

Forthisbook,wewillbeusingversion1.3.10.Weneedtoputtheactivator/binfolderintheOSPATH.Ifyouwant,youcaninstallActivatorusingtheterminal,likethis:

Ifyouwant,youcaninstallActivatorusingtheterminal,likethis:

$cd/usr/local/

$wgethttps://downloads.typesafe.com/typesafe-

activator/1.3.10/typesafe-activator-1.3.10-minimal.zip

$tar-xzftypesafe-activator-1.3.10-minimal.zip

$rm-rftypesafe-activator-1.3.10-minimal.zip

$sudoecho'exportPATH=$PATH:/usr/local/typesafe-activator-

1.3.10-minimal/bin'>>~/.bashrc

$source>>~/.bashrc

Inordertotestyourinstallation,executethiscommand:

$activatornewReactiveWebStore

TheprecedingcommandwillBootstrapanarchitectureforyouwithScala,Akka,Playframework,andSBT.

Activatorwillaskyouaseriesofquestionslikesuchaswhattemplatesyoumightliketouse.ThereareacoupleoftemplatesforJavaapplications,Scalaapplications,Akkaapplications,andPlayapplications.Fornow,wewillpickoption6)play-scala.

https://www.lightbend.com/community/core-tools/activator-and-sbt

https://www.lightbend.com/activator/download

https://downloads.typesafe.com/typesafe-activator/1.3.10/typesafe-activator-1.3.10-minimal.zip

ThefirsttimeyourunActivator,itcouldtakesometime,becauseitwilldownloadallthedependenciesfromtheweb.WhenActivatorfinishes,youshouldseeafoldercalledReactiveWebStoreinyourfilesystem.

Thecommand$activatornewReactiveWebStoreshowsthefollowingresult:

YoushouldentertheReactiveWebStorefolderifyoutype$llintotheconsole,andyoushouldalsoseethefollowingstructure:

diego@4winds:~/bin/activator-1.3.10-minimal/bin/ReactiveWebStore$

ll

total52

drwxrwxr-x9diegodiego4096Mai1419:03./

drwxr-xr-x3diegodiego4096Mai1419:03../

drwxrwxr-x6diegodiego4096Mai1419:03app/

drwxrwxr-x2diegodiego4096Mai1419:03bin/

-rw-rw-r--1diegodiego346Mai1419:03build.sbt

drwxrwxr-x2diegodiego4096Mai1419:03conf/

-rw-rw-r--1diegodiego80Mai1419:03.gitignore

drwxrwxr-x2diegodiego4096Mai1419:03libexec/

-rw-rw-r--1diegodiego591Mai1419:03LICENSE

drwxrwxr-x2diegodiego4096Mai1419:03project/

drwxrwxr-x5diegodiego4096Mai1419:03public/

-rw-rw-r--1diegodiego1063Mai1419:03README

drwxrwxr-x2diegodiego4096Mai1419:03test/

Thecontentisexplainedasfollows:

app:ThisisthePlayframeworkapplicationfolderwherewewilldotheScalawebdevelopment.build.sbt:Thisisthebuildfile;asyoucansee,ActivatorhasgeneratedtheSBTbuildconfigforus.conf:ThisholdstheapplicationconfigfilessuchasloggingandScala/Playappconfig.project:ThisistheSBTprojectfolderwherewedefineSBTpluginsandSBTversion.test:Thisholdsthetestsourcecodeforourapplication.public:ThisholdsstaticHTMLassetslikeImages,CSS,andJavaScriptcode.bin:ThisholdsacopyoftheactivatorscriptforLinux/MacandWindows.libexec:ThisholdstheActivatorjar.Thisisprettyuseful,becauseActivatorhaspackeditselfwithourapplication.So,let'ssayyoupushthisapplicationforGitHub-whensomeoneneedstoaccessthisappanddownloaditfromGitHub,theSBTfilewillbethere,sotheywon'tneedtodownloaditfromtheInternet.Thisisespeciallyusefulwhenyouareprovisioninganddeployingapplicationsinproduction,whichthisbookwillcoverindetailinChapter10,ScalingUp.

ActivatorshellActivatorallowsyoutorunREPLlikewedidinScalaandSBT.InordertogetREPLaccess,youneedtotypethefollowingontheconsole:

$activatorshell

Activatorhasplentyoftasksthatyoucanuse.Inordertoknowalltheavailablecommands,youcantype$activatorhelpontheconsole.

Activator-compiling,testing,andrunningLet'sgettobusinessnow.Wewillcompile,runtests,andrunourwebapplicationusingActivatorandSBT.Firstofall,let'scompile.Type$activatorcompileontheconsoleasfollows:

$activatorcompile


activatorcompile

[info]Loadingglobalpluginsfrom/home/diego/.sbt/0.13/plugins

[info]Loadingprojectdefinitionfrom/home/diego/bin/activator-

1.3.10-minimal/bin/ReactiveWebStore/project

[info]SetcurrentprojecttoReactiveWebStore(inbuild

file:/home/diego/bin/activator-1.3.10-

minimal/bin/ReactiveWebStore/)

[info]Updating{file:/home/diego/bin/activator-1.3.10-

minimal/bin/ReactiveWebStore/}root...

[info]Compiling14Scalasourcesand1Javasourceto

/home/diego/bin/activator-1.3.10-

minimal/bin/ReactiveWebStore/target/scala-2.11/classes...

[success]Totaltime:154s,completed14/05/201619:28:03


Let'srunourtestsnowwiththecommand$activatortest.

Finally,it'stimetorunyourapplication.Type$activatorrunontheconsole.

Openyourwebbrowser,andgototheURL:http://localhost:9000.

Youshouldseeascreenlikethefollowing:

SummaryCongratulations!You'vejustBootstrappedyourfirstScala/Playframeworkfirst.Activatormakesourlifeeasier.Asyoucansee,withthreecommands,wewereabletogetasiteupandrunning.YoucoulddothesamewithjustSBT,however,itwouldtakemoretime,becausewewouldneedtogetallthedependencies,configureallthesourcecodestructure,andaddsomesampleHTMLandScalacode.ThankstoActivator,wedon'tneedtodoanyofthat.However,wecanstillchangealltheSBTfilesandconfigsasperourwish.ActivatorisnottightwithScalaorourapplicationcode,sinceitismorelikeatemplate-basedcodegenerator.

Inthenextchapter,wewillbeimprovingtheapplicationbyaddingvalidations,databasepersistence,ReactiveMicroservicescallingusingRxScalaandScala,andmuchmore.

Chapter3.DevelopingtheUIwithPlayFrameworkInthepreviouschapter,weperformedbootstrappingonourapplicationusingActivator.Inthischapter,wewillcontinuedevelopingourwebapplicationusingScalaandPlayframework.Playframeworkisgreatforwebdevelopmentbecauseitissimpletouse,andatthesametime,verypowerful.Thisisbecauseitusestop-notchreactivesolutionslikespray,Akka,andAkkaStreamunderthehood.Forthischapter,wewillcreatethebasicUIforsomepartsofourreactivewebsolutionbyaddingvalidationandanin-memorystoresoyoucanfeeltheapplicationworking.WewillusealittlebitofCSSforstyling,andJavaScriptforsomesimplevisualizations.

Inthischapter,wewillcoverthefollowingtopics:

BasicsofwebdevelopmentwithScalaandPlayframeworksCreatingyourmodelsWorkingwithviewsandvalidationsWorkingwithsessionscopes

GettingstartedLet'shavealookatthepreviewofReactiveWebStore--theapplicationthatwewillbuild.

Fornow,wewillbuildthreesimpleoperations--Create,Retrieve,Update,andDelete(CRUD)inordertomanageproducts,productreviews,andproductimages.Wewillcreatemodels,controllers,views,androutesforeachCRUD.

Let'sgetstarted.Firstofall,weneedtodefineourmodels.ThemodelsneedtobelocatedatReactiveWebStore/app/models.ModelsaretheCOREofthesystemandtheyrepresenttheentity.WewillusethisentitylatertostoreandretrievedatafromadatabaselateroninChapter6,PersistencewithSlick.OurmodelsshouldnothaveanyUIlogic,sinceweshouldusecontrollersforUIlogic.

CreatingourmodelsForourproductmodel,wehaveasimpleScalacaseclassinProduct.scalaasfollows:

packagemodels

caseclassProduct

(varid:Option[Long],

varname:String,

vardetails:String,

varprice:BigDecimal)

{

overridedeftoString:String=

{

"Product{id:"+id.getOrElse(0)+",name:"+name+",

details:"+details+",price:"+price+"}"

}

}

AproductcanhaveanoptionalID,aname,details,andaprice.WealsooverridethetoStringmethodjustforthesakeofsimplicityforlogging.Wealsoneedtodefinemodelsforimageandreview.

ThefollowingisthereviewmodelfromReview.scala:

packagemodels

caseclassReview


varproductId:Option[Long],

varauthor:String,

varcomment:String)

{

overridedeftoString:String={

"Review{id:"+id+",productId:"+

productId.getOrElse(0)+",author:"+author+",comment:

"+comment+"}"

}

}

Forareviewmodel,wehaveanoptionalID,anoptionalproductId,oneauthor,andacomment.Validationswillbedoneontheviews.Nowlet'sgofortheimagemodel.

TheimagemodelcanbefoundinImage.scalaasfollows:

packagemodels

caseclassImage



varurl:String){


"Image{productId:"+productId.getOrElse(0)+",url:"

+url+"}"

}

}

Foranimagemodel,wehaveanoptionalID,anoptionalproductId,andtheimageURL.

ThePlayframeworkdoestherouting,andweneedtodefinetheroutesatReactiveWebStore/conf/routes.KeepinmindthatthePlayframeworkwillvalidatealltheroutes,soyouneedtospecifyvalidpackagesandclasses.Playalsocreatessomethingcalledreversecontroller,whichwewilluselaterinthechapter.Fornow,let'sdefinetheroutes.ReversecontrollerisgeneratedbythePlayframeworkwithanactionmethodwhichisthesameasthatoftheoriginalcontrollerwiththesamesignature,butitreturnsplay.api.mvc.Callinsteadofplay.api.mvc.Action.

CreatingroutesThePlayframeworkCRUDoperations'routesforproduct,image,andreviewareasfollows:

#Routes

#Thisfiledefinesallapplicationroutes(Higherpriorityroutesfirst)

#~~~~

GET/controllers.HomeController.index

GET/assets/*filecontrollers.Assets.at(path="/public",file)

#

#CompleteCRUDforProduct

#

GET/productcontrollers.ProductController.index

GET/product/addcontrollers.ProductController.blank

POST/product/controllers.ProductController.insert

POST/product/:idcontrollers.ProductController.update(id:Long)

POST/product:id/removecontrollers.ProductController.remove(id:Long)

GET/product/details/:idcontrollers.ProductController.details(id:Long)

#

#CompleteGRUDforReview

#

GET/reviewcontrollers.ReviewController.index

GET/review/addcontrollers.ReviewController.blank

POST/review/controllers.ReviewController.insert

POST/review/:idcontrollers.ReviewController.update(id:Long)

POST/review:id/removecontrollers.ReviewController.remove(id:Long)

GET/review/details/:idcontrollers.ReviewController.details(id:Long)

#

#CompleteCRUDforImage

#

GET/imagecontrollers.ImageController.index

GET/image/addcontrollers.ImageController.blank

POST/image/controllers.ImageController.insert

POST/image/:idcontrollers.ImageController.update(id:Long)

POST/image:id/removecontrollers.ImageController.remove(id:Long)

GET/image/details/:idcontrollers.ImageController.details(id:Long)

Theroutesworklikethis--FirstyouneedtodefinetherestverbsuchasGET,POST,PUT,DELETE,andthenyouputinaPATHlike/image.Finally,youspecifywhichcontrollerfunctionwillhandlethatroute.Nowwehavetheroutesinplace,wecanmovetothecontrollers.Wewilldefinethecontrollersforproduct,imageandreview.

Alltheroutesfollowthesamelogic.Firstwesendtheusertothewebpagewherewelistalltheitems(products,images,reviews)--thisisrepresentedbyGET/resource,wheretheresourcecanbeanimage,product,orreview,forinstance.Inordertogetaspecificresource,oftenbyID,wegivethecommandGET/resource(product,revieworimage)/ID.POST/resourceisusedtoperformtheUPDATE.

Inordertocreateanewitem(product,review,orimage),thepatternisGET/resource/addandPOST/resource/.Youmaywonderwhytherearetworoutestoperformaninsert.Well,that'sbecausefirstofallweneedtoloadthewebpage,andsecondly,whentheformissubmitted,weneedanewroutetohandlethevalues.Therearetworoutesforanupdateaswellforthesamereason.IfyouwanttoDELETEaresource,thepatternisPOST/resource/ID/remove.Lastly,wehavethedetailsoftheoperation,whichisusedtoshowdetailedinformationwithregardtoaspecificitem--thepatternisGET/resource/details/ID.Withsixroutes,wecandoacompleteCRUDforaresourcesuchasproduct,image,andreview,oranyotherfutureresourcethatyoumayaddtothisapplicationoryourownapplications.

CreatingourcontrollersNowlet'smovetothecontrollersusedonthepreviousroutes.ThecontrollersneedtobelocatedatReactiveWebStore/app/controllers.Controllersareboundbetweenviews(UI),modelsandservice,whichareresponsibleforbusinessoperations.It'salwaysimportanttoseparateUIlogic,whichtendstobespecific,frombusinesslogic,whichtendstobemoregeneric,andoften,waymoreimportant.

Let'shavealookattheproductcontrollerinProductController.scalainthefollowingcode:

@Singleton

classProductController@Inject()(valmessagesApi:MessagesApi,val

service:IProductService)extendsControllerwithI18nSupport{

valproductForm:Form[Product]=Form(

mapping(

"id"->optional(longNumber),

"name"->nonEmptyText,

"details"->text,

"price"->bigDecimal

)(models.Product.apply)(models.Product.unapply))

defindex=Action{implicitrequest=>

valproducts=service.findAll().getOrElse(Seq())

Logger.info("indexcalled.Products:"+products)

Ok(views.html.product_index(products))

}

defblank=Action{implicitrequest=>

Logger.info("blankcalled.")

Ok(views.html.product_details(None,productForm))

}

defdetails(id:Long)=Action{implicitrequest=>

Logger.info("detailscalled.id:"+id)

valproduct=service.findById(id).get

Ok(views.html.product_details(Some(id),

productForm.fill(product)))

}

definsert()=Action{implicitrequest=>

Logger.info("insertcalled.")

productForm.bindFromRequest.fold(

form=>{

BadRequest(views.html.product_details(None,form))

},

product=>{

valid=service.insert(product)

Redirect(routes.ProductController.index).flashing("success"

->Messages("success.insert",id))

})

}

defupdate(id:Long)=Action{implicitrequest=>

Logger.info("updatedcalled.id:"+id)


form=>{


form)).flashing("error"->"Fixtheerrors!")

},

product=>{

service.update(id,product)

Redirect(routes.ProductController.index).

flashing("success"->Messages("success.update",

product.name))

})

}

defremove(id:Long)=Action{

service.findById(id).map{product=>

service.remove(id)

Redirect(routes.ProductController.index).flashing("success"->

Messages("success.delete",product.name))

}.getOrElse(NotFound)

}

}

ThePlayframeworkusesdependencyinjectionandinversionofcontrolusingGoogleGuice.So,youcanseeatthetopofthecontrollerthatwehavetheannotations@Singletonand@Inject.SingletonmeansthatGuicewillcreateasingleinstanceoftheclasstohandleallrequests.Injectmeansweareinjectingotherdependenciesintoourcontroller,forinstance,weinjectMessagesApiinordertohavethePlayframeworkinternalizationsupportforstringmessages,andIProductService,thatis,theproductservicethatwewillcoverlaterinthischapter.

WealsoneedtoextendthePlayclass,play.api.mvc.Controller.Eachfunctioninacontrollerneedstoreturnanaction.Thisactioncouldbeaview.ThePlayframeworkcompilesalltheviewsintoScalaclasses,soyoucansafelyreferencethemintoyourcontrollerscode.

AllbusinessoperationsaredelegatedtoatraitcalledIProductService,whichwewillcoverlaterinthischapter.WealsologsomeinformationusingtheLoggerclass.PlayFrameworkusesLogbackasthedefaultloggingsolution.Let'stakeacloserlookateachcontrollerfunctionnow.

TheindexfunctioncallsIProductService,andfindsalltheavailableproducts.Iftherearenoproductsavailable,itreturnsanemptysequence,andthencallstheproductUIpassingthecollectionofproducts.

Theblankfunctionrendersablankproductform,sotheusercanhaveablankproductformontheUIinordertoadddata(insertoperation).Playframeworkworkswithformbinding.

So,ineachcontroller,youneedtodefinehowyourformlooksontheUI.Thatformmappingisdoneusingplay.api.data.Form.YoucanseethemappingontheimmutablevariablecalledproductForm.Themappingisbetweentheview(UI)andthemodelcalledproduct.KeepinmindthatthenamefieldismappedasNonEmptyText,whichmeansPlaywon'tacceptnullorblankvalues.Thisisagreatfuture,becausewecandovalidationsinadeclarativewaywithouthavingtowritecode.PriceisdefinedasBigDecimal,soPlaywon'taccepttext,butonlynumbers.

ThedetailsfunctionretrievesaproductusingIProductService,andredirectstotheview.However,beforedoingtheredirect,itbindsthedatawiththeformsotheUIwillloadwithallthedataintotheHTMLinputs.

Wealsohavetheinsertandupdatemethods.Theyareallconstructedwithafoldmethod.Thefoldmethodhasleftandright,whichmeanserrororok.Thefoldfunctioniscalledfromthemappedformandiftherearenovalidationerrors,itgoesright,butiftherearevalidationserrors,itgoesleft.That'saverysimpleandcleanwaytocodetheupdateandinsertflows.Withfold,wedon'tneedcodeforanifstatement.OncethevalidationisOK,wecallIProductServicetodoaninsertorupdate,andthenweperformaredirecttotheview.Messagesarepassedviascope.Playhasoptionsforscope--sessionorFlash.Sessionisformultiplerequests,andthevaluewillbestoredintheclientside.Flashisarequestscope,andmostofthetimesthatiswhatyouneedtouse.HereweareusingtheFlashscope,soitwillonlyexitduringthatspecificrequest.ThisfeatureisusedtopassInternationalizationmessages(i18n),whicharetheresultoftheaction.Allthei18nmessagesneedtobedefinedatReactiveWebStore/conf/messagesasfollows:

success.delete=OK'{0}'deleted!

success.insert=OK'{0}'created!

success.update=OK'{0}'updated!

error.notFound=NothingFoundwithID{0,number,0}

error.number=Notavalidnumber

error.required=Missingvaluehere

Lastly,wehavetheremovemethod.Firstofall,weneedtomakesuretheproductexists,sowedoafindByIdusingIProductService,andthenweapplyamapfunction.Iftheproductdoesn'texist,thePlayframeworkhasprebuiltHTTPerrorcodemessageslikeNotFound.Iftheproductexists,weremoveitusingIProductService,andthenweredirecttotheUIwithaflashingmessage.Nowlet'sseetheimageandreviewcontrollers.

Thereviewcontroller,ReviewController.scala,isasfollows:

@Singleton

classReviewController@Inject()

(valmessagesApi:MessagesApi,

valproductService:IProductService,

valservice:IReviewService)

extendsControllerwithI18nSupport{

valreviewForm:Form[Review]=Form(

mapping(


"productId"->optional(longNumber),

"author"->nonEmptyText,

"comment"->nonEmptyText

)(models.Review.apply)(models.Review.unapply))


valreviews=service.findAll().getOrElse(Seq())

Logger.info("indexcalled.Reviews:"+reviews)

Ok(views.html.review_index(reviews))

}



Ok(views.html.review_details(None,

reviewForm,productService.findAllProducts))

}



valreview=service.findById(id).get

Ok(views.html.review_details(Some(id),

reviewForm.fill(review),productService.findAllProducts))

}



reviewForm.bindFromRequest.fold(

form=>{

BadRequest(views.html.review_details(None,

form,productService.findAllProducts))

},

review=>{

if(review.productId==null||

review.productId.getOrElse(0)==0){

Redirect(routes.ReviewController.blank).flashing("error"->

"ProductIDCannotbeNull!")

}else{

Logger.info("Review:"+review)


review.productId.getOrElse(0)==0)thrownew

IllegalArgumentException("ProductIdCannotBeNull")

valid=service.insert(review)

Redirect(routes.ReviewController.index).flashing("success"-

>Messages("success.insert",id))

}

})

}




form=>{


form,productService.findAllProducts)).flashing("error"->

"Fixtheerrors!")

},

review=>{

service.update(id,review)


>Messages("success.update",review.productId))

})

}


service.findById(id).map{review=>

service.remove(id)


>Messages("success.delete",review.productId))


}

}

Thereviewcontrollerfollowsthesameideasandstructureastheproductcontroller.TheonlymaindifferenceisthathereweneedtoInjectIProductService,becauseareviewneedstobelongtoaproduct.ThenweneedtouseIProductServiceinordertofindAllProduct,becauseinthereviewview,wewillhaveSelectBoxwithalltheavailableproducts.

Theimagecontroller,ImageController.scala,isasfollows:

@Singleton

classImageController@Inject()



valservice:IImageService)


valimageForm:Form[Image]=Form(

mapping(



"url"->text

)(models.Image.apply)(models.Image.unapply))


valimages=service.findAll().getOrElse(Seq())

Logger.info("indexcalled.Images:"+images)

Ok(views.html.image_index(images))

}



Ok(views.html.image_details(None,

imageForm,productService.findAllProducts))

}



valimage=service.findById(id).get

Ok(views.html.image_details(Some(id),

imageForm.fill(image),productService.findAllProducts))

}



imageForm.bindFromRequest.fold(

form=>{

BadRequest(views.html.image_details(None,form,

productService.findAllProducts))

},

image=>{

If(image.productId==null||

image.productId.getOrElse(0)==0){

Redirect(routes.ImageController.blank).

flashing("error"->"ProductIDCannotbeNull!")

}else{

if(image.url==null||"".equals(image.url))image.url

="/assets/images/default_product.png"

valid=service.insert(image)

Redirect(routes.ImageController.index).

flashing("success"->Messages("success.insert",id))

}

})

}




form=>{

Ok(views.html.image_details(Some(id),form,

null)).flashing("error"->"Fixtheerrors!")

},

image=>{

service.update(id,image)



image.id))

})

}


service.findById(id).map{image=>

service.remove(id)

Redirect(routes.ImageController.index).flashing("success"

->Messages("success.delete",image.id))


}

}

ImagereviewworksinasimilarwaytoReviewController.WeneedIProductServicetogetalltheservices.

WorkingwithservicesServicesarewhereweputthebusinesslogic.WewilllookatreactivepersistenceinChapter6,PersistencewithSlick.Rightnow,wedon'thaveadatabasetopersistinformation,so,fornow,wewilldoanin-memorypersistence.

Firstwewilldefinethecontractofourservices.ThisistheBaseAPIthatwewilluseinthecontrollers.Let'stakealookatthefollowingtraitinBaseService.scala:

packageservices

importjava.util.concurrent.atomic.AtomicLong

importscala.collection.mutable.HashMap

traitBaseService[A]{

varinMemoryDB=newHashMap[Long,A]

varidCounter=newAtomicLong(0)

definsert(a:A):Long

defupdate(id:Long,a:A):Boolean

defremove(id:Long):Boolean

deffindById(id:Long):Option[A]

deffindAll():Option[List[A]]

}

Intheprecedingcode,wehaveanin-memorymutableHashMap,whichisinourmemorydatabasewherewewillstoreproducts,images,andreviews.WealsohaveanatomiccounterwithwhichwecangenerateIDsforourmodels.ThisisatraitusingGenerics--asyoucansee,herewehavealltheoperationswithA,whichwillbespecifiedlater.Nowwecanmovetheserviceimplementationforproduct,review,andimage.

TheProductService.scalapackageisasfollows:

packageservices

importmodels.Product

importjavax.inject._

traitIProductServiceextendsBaseService[Product]{

definsert(product:Product):Long

defupdate(id:Long,product:Product):Boolean


deffindById(id:Long):Option[Product]

deffindAll():Option[List[Product]]

deffindAllProducts():Seq[(String,String)]

}

@Singleton

classProductServiceextendsIProductService{

definsert(product:Product):Long={

valid=idCounter.incrementAndGet()

product.id=Some(id)

inMemoryDB.put(id,product)

id

}

defupdate(id:Long,product:Product):Boolean={

validateId(id)

product.id=Some(id)

inMemoryDB.put(id,product)

true

}

defremove(id:Long):Boolean={

validateId(id)

inMemoryDB.remove(id)

true

}

deffindById(id:Long):Option[Product]={

inMemoryDB.get(id)

}

deffindAll():Option[List[Product]]={

if(inMemoryDB.values==Nil||

inMemoryDB.values.toList.size==0)returnNone

Some(inMemoryDB.values.toList)

}

privatedefvalidateId(id:Long):Unit={

valentry=inMemoryDB.get(id)

if(entry==null)thrownewRuntimeException("Couldnotfind

Product:"+id)

}

deffindAllProducts():Seq[(String,String)]={

valproducts:Seq[(String,String)]=this

.findAll()

.getOrElse(List(Product(Some(0),"","",0)))

.toSeq

.map{product=>(product.id.get.toString,product.name)}

returnproducts

}

}

Inthelastcode,wedefinedatraitcalledIProductService,whichextendsBaseServicewithagenericapplytoproduct.TheProductServicepackageimplementsIProductService.InScala,wecanhavemultipleclassesinthesameScalafile,sothereisnoneedtocreatedifferentfiles.

Thecodeisverystraightforward.ThereisautilitymethodherecalledfindAllProducts,whichisusedbyreviewandimagecontrollers.Herewegetalltheelementsonthein-

memoryhashmap.Iftherearenoelements,wereturnalistwithemptyproduct.ThenwemapthelisttoaSeqoftuple,whichisrequiredbytheSelectBoxcheckboxthatwewillhaveintheview(UI).Nowlet'sgofortheimageandreviewservicesasfollows:

packageservices


importmodels.Image



traitIImageServiceextendsBaseService[Image]{

definsert(image:Image):Long

defupdate(id:Long,image:Image):Boolean


deffindById(id:Long):Option[Image]

deffindAll():Option[List[Image]]

}

@Singleton

classImageServiceextendsIImageService{

definsert(image:Image):Long={

valid=idCounter.incrementAndGet();

image.id=Some(id)

inMemoryDB.put(id,image)

id

}

defupdate(id:Long,image:Image):Boolean={

validateId(id)

image.id=Some(id)

inMemoryDB.put(id,image)

true

}


validateId(id)


true

}

deffindById(id:Long):Option[Image]={

inMemoryDB.get(id)

}

deffindAll():Option[List[Image]]={

if(inMemoryDB.values.toList==null||



}



If(entry==null)thrownewRuntimeException("Couldnotfind

Image:"+id)

}

}

Intheprecedingcode,wehavesomethingprettysimilartothatofProductService.WehaveatraitcalledIImageServiceandtheImageServiceimplementation.Nowlet'sgoforthereviewserviceimplementationinReviewService.scalaasfollows:

packageservices


importmodels.Review



traitIReviewServiceextendsBaseService[Review]{

definsert(review:Review):Long

defupdate(id:Long,review:Review):Boolean


deffindById(id:Long):Option[Review]

deffindAll():Option[List[Review]]

}

@Singleton

classReviewServiceextendsIReviewService{

definsert(review:Review):Long={


review.id=Some(id)

inMemoryDB.put(id,review)

id

}

defupdate(id:Long,review:Review):Boolean={

validateId(id)

review.id=Some(id)

inMemoryDB.put(id,review)

true

}


validateId(id)


true

}

deffindById(id:Long):Option[Review]={

inMemoryDB.get(id)

}

deffindAll():Option[List[Review]]={

if(inMemoryDB.values.toList==null||



}



If(entry==null)thrownewRuntimeException("Couldnotfind

Review:"+id)

}

}

Intheprecedingcode,wehavetheIReviewServicetraitandtheReviewServiceimplementation.Wehavevalidationsontheserviceaswellasagoodpractice.

ConfiguringtheGuicemoduleWeinjectedclassesusing@Injectinourcontrollers.Theinjectionhappensbasedonatrait;weneedtodefineaconcreteimplementationforthetraitsweinjected.ThePlayframeworklooksforGuiceinjectionsatthelocationReactiveWebStore/app/Module.scala.Okay,solet'sdefineourinjectionsforthethreecontrollerswejustcreated.

TheGuicemoduleisfoundinModule.scalaasfollows:

importcom.google.inject.AbstractModule

importjava.time.Clock

importservices.{ApplicationTimer}

importservices.IProductService

importservices.ProductService

importservices.ReviewService

importservices.IReviewService

importservices.ImageService

importservices.IImageService

/**

*ThisclassisaGuicemodulethattellsGuicehowtobindseveral

*differenttypes.ThisGuicemoduleiscreatedwhenthePlay

*applicationstarts.

*Playwillautomaticallyuseanyclasscalled`Module`thatisin

*therootpackage.Youcancreatemodulesinotherlocationsby

*adding`play.modules.enabled`settingstothe`application.conf`

*configurationfile.

*/

classModuleextendsAbstractModule{

overridedefconfigure()={

//UsethesystemclockasthedefaultimplementationofClock

bind(classOf[Clock]).toInstance(Clock.systemDefaultZone)

//AskGuicetocreateaninstanceofApplicationTimer

//whentheapplicationstarts.

bind(classOf[ApplicationTimer]).asEagerSingleton()

bind(classOf[IProductService]).to(classOf[ProductService]).

asEagerSingleton()

bind(classOf[IReviewService]).to(classOf[ReviewService]).

asEagerSingleton()

bind(classOf[IImageService]).to(classOf[ImageService]).

asEagerSingleton()

}

}

Sowejustneedtoaddbindwithourtraitsforthecontrollers,andthenpointtothecontrollerimplementation.Theyshouldalsobecreatedassingletons,asthePlayframeworkstartsourapplication.Hereyoualsocandefineanyotherconfigurationorinjectionthatourapplicationmayneed.Thelastcodedefinesthreeservices:productservice,IReviewService,andIImageService.

Workingwithviews(UI)ThePlayframeworkworkswithaScala-basedtemplatingenginecalledTwirl.TwirlwasinspiredbyASP.NETRazor.Twirliscompactandexpressive;youwillseewecandomorewithless.Twirltemplatefilesaresimpletextfiles,however,thePlayframeworkcompilesthetemplatesandturnsthemintoScalaclasses.YoucanmixHTMLwithScalasmoothlyinTwirl.

TheUIwillbecompiledintoaScalaclass,thatcanandwillbereferencedatourcontrollers,becausewecanroutetoaview.Thenicethingaboutitisthatthismakesourcodingwaysafer,sincewehavethecompilercheckingforus.ThebadnewsisthatyouneedtocompileyourUI,otherwise,yourcontrollerswon'tfindit.

Previouslyinthischapter,wedefinedcontrollersforproducts,images,andreviews,andwewrotethefollowingcode:


Withtheprecedingcode,weredirecttheusertoablankpageforproductssothattheusercancreateanewproduct.WealsocanpassparameterstotheUI.SinceitisallScalacode,youareactuallyjustcallingafunctionasfollows:

valproduct=service.findById(id).get

Ok(views.html.product_details(Some(id),productForm.fill(product)))

Intheprecedingcode,wecalltheservicetoretrieveaproductbyID,andthenpasstheobjecttotheUIwiththeformbeingfilled.

Let'scontinuebuildingourapplicationandcreatetheUIfortheproducts,reviews,andimages.SincewearedoingaCRUD,wewillneedmorethanonetemplatefileperCRUD.Wewillneedthefollowingstructure:

IndexTemplateListallitemsLinktoeditoneitemLinktoremoveoneitemLinktocreateanewItem

DetailTemplateHTMLFormtocreateanewItemHTMLformtoeditanexistingitem(forupdate)

Havingsaidthat,wewillhavethefollowingfiles:

ForProducts:product_index.scala.htmlproduct_details.scala.html

ForImage:

image_index.scala.htmlimage_details.scala.html

ForReviews:review_index.scala.htmlreview_details.scala.html

Forthesakeofcodereuse,wewillcreateanotherfilecontainingthebasicstructureofourUI,likeCSSimports(CSSneedstobelocatedatReactiveWebStore\public\stylesheets),JavaScriptimports,andpagetitlesothatwedon'tneedtorepeatthatinallthetemplatesforeachCRUD.Thispagewillbecalled:main.scala.html.

AlltheUIcodeshouldbelocatedatReactiveWebStore/app/views.

ThemainScalawiththeUIindexforallCRUDoperationsisinmain.scala.html,asfollows:

@(title:String)(content:Html)(implicitflash:Flash)

<!DOCTYPEhtml>

<htmllang="en">

<head>

<title>@title</title>

<linkrel="shortcuticon"type="image/png"

href="@routes.Assets.at("images/favicon.png")">

<linkrel="stylesheet"media="screen"

href="@routes.Assets.at("stylesheets/main.css")">


href="@routes.Assets.at("stylesheets/bootstrap.min.css")">

<scriptsrc="@routes.Assets.at("javascripts/jquery-

1.9.0.min.js")"type="text/javascript"></script>

<scriptsrc="@routes.Assets.at("javascripts/bootstrap.js")"

type="text/javascript"></script>

<scriptsrc="@routes.Assets.at("javascripts/image.js")"


</head>

<body>

<center><ahref='/'><imgheight='42'width='42'

src='@routes.Assets.at("images/rws.png")'></a>

<h3>@title</h3></center>

<divclass="container">

@alert(alertType:String)={

@flash.get(alertType).map{message=>

<divclass="alertalert-@alertType">

<buttontype="button"class="close"data-

dismiss="alert">×</button>

@message

</div>

}

}

@alert("error")

@alert("success")

@content

<ahref="/"></a><BR>

<buttontype="submit"class="btnbtn-primary"

onclick="window.location.href='/';">

ReactiveWebStore-Home

</button>

</div>

</body>

</html>

Intheprecedingcode,firstofall,thereisthefollowinglineattheverytop:


ThismeansthatwedefinetheparametersthisUIcanreceive.Hereweexpectastringtitle,whichwillbethepagetitle,andtherearesomecurryingvariablesaswell.YoucangetmoredetailsaboutcurryinginChapter1,IntroductiontoFP,Reactive,andScala.Soincurrying,therearetwothings:FirstisHTML,whichmeansyoucanpassHTMLcodetothisfunction,andsecond,wehaveFlashwhichthePlayframeworkwillpassforus.Flashisusedtogetparametersbetweenrequests.

Asyoucansee,laterinthecodewehave@title,whichmeansweretrievethetitleoftheparameters,andaddthevaluetotheHTML.Wealsoprintanyerrormessageoranyvalidationsissues,ifpresent,[email protected],butwedonotputhard-codedpaths.Instead,weusetherouterslike@routes.Assets.at.TheJavascriptsstillneedtobelocatedatReactiveWebStore\public\javascripts.

Nowothertemplatescanworkwith@main(..),andtheydon'tneedanydeclarationofJavascriptorCSS.TheycanaddanextraHTMLcode,[email protected],fortheproducts,thecontentwillbeHTMLproductcontent,andsoonforreviews,andimages.NowwecanmovefortheproductsUI.

Productindex:UIindexforproductsproduct_index.scala.html

@(products:Seq[Product])(implicitflash:Flash)

@main("Products"){

@if(!products.isEmpty){

<tableclass="tabletable-striped">

<tr>

<th>Name</th>

<th>Details</th>

<th>Price</th>

<th></th>

</tr>

@for(product<-products){

<tr>

<td><ahref="@routes.ProductController.

details(product.id.get)">@product.name</a></td>

<td>@product.details</td>

<td>@product.price</td>

<td><formmethod="post"action=

"@routes.ProductController.remove(product.id.get)">

<buttonclass="btnbtn-link"type="submit">

<iclass="icon-trash"></i>Delete</button>

</form></td>

</tr>

}

</table>

}

<p><ahref="@routes.ProductController.blank"class=

"btnbtn-success"><iclass="icon-plusicon-white">

</i>AddProduct</a></p>

}

Asyoucansee,thereisHTMLmixedwithScalacode.EverytimeyouneedtorunHTML,youjustrunit,andwhenyouneedrunScalacode,youneeduseaspecialcharacter,@.Attheverytopofthetemplate,youcanseethefollowingcode:


SincethisisScalacodeintheend,andwillbecompiled,weneedtodefinewhatparametersthisUItemplatecanreceive.Hereweexpectasequenceofproducts.ThereisalsoacurryingimplicitvariablecalledFlash,whichwillbeprovidedbythePlayframework,andwewilluseitforthemessagedisplay.Wealsohavethecode-@main("Products"){..}.ThismeansthatwecallthemainScalatemplateandaddextraHTML--theproductHTML.ForthisproductUI,welistalltheproductsbasedonthesequenceofproducts.Asyoucansee,wedefineanHTMLtable.Wealsovalidateifthesequenceisnotemptybeforelistingalltheproducts.

Nowwecangoforthedetailspageforproductsinproduct_details.scala.htmlasfollows:

@(id:Option[Long],product:Form[Product])(implicitflash:Flash)

@importplay.api.i18n.Messages.Implicits._

@importplay.api.Play.current

@main("Product:"+product("name").value.getOrElse("")){

@if(product.hasErrors){

<divclass="alertalert-error">



Sorry!Someinformationdoesnotlookright.Couldyou

reviewitpleaseandre-submit?

</div>

}

@helper.form(action=if(id.isDefined)

routes.ProductController.update(id.get)else

routes.ProductController.insert)

{

@helper.inputText(product("name"),'_label->"Product

Name")

@helper.inputText(product("details"),'_label->"Product

Details")

@helper.inputText(product("price"),'_label->"Price")

<divclass="form-actions">

<buttontype="submit"class="btnbtn-primary">

@if(id.isDefined){UpdateProduct}else{NewProduct}

</button>

</div>

}

}

ForthisprecedingUI,attheverytop,wehavethefollowingline:


ThismeansthatweexpectanIDwhichiscompletelyoptional.ThisIDisusedtoknowifwearedealingwithaninsertscenariooranupdatescenario,becauseweusethesameUIforbothinsertandupdate.Wealsogettheproductform,whichwillbepassedthroughProductController,andwereceiveFlash,whichwillbeprovidedbythePlayframework.

WeneedtodosomeimportsontheUIsothatwecangetaccesstothePlayframeworki18nsupport.Thisisdonebythefollowing:



LikethepreviousUI,werenderthisUIwithinthemainScalaUI.Sowedon'tneedtospecifyJavaScriptandCSSagain.Thisisdonebythefollowingcode:

@main("Product:"+product("name").value.getOrElse("")){..}

Nextwecheckifthereareanyvalidationerrors.Ifthereare,theuserswillneedtofixtheerrorsbeforemovingon.Thisisdonebythefollowingcode:





Sorry!Someinformationdoesnotlookright.Couldyoureview

itpleaseandre-submit?

</div>

}

Nowisthetimetocreatetheproductform,which,intheend,willbemappedtoHTMLinputboxes.Wedothiswiththefollowingcode:



routes.ProductController.insert){

@helper.inputText(product("name"),'_label->"ProductName")


Details")





</button>

</div>

}

@helper.formisaspecialhelperprovidedbythePlayframeworktocreateHTMLformseasily.So,theactionisthetargetwheretheformwillbesubmitted.Weneedtodoanifhere,sinceweneedtoknowifitisanupdateoraninsert.Thenwemapallthefieldswehaveforourproductmodelwiththiscode:


@helper.inputText(product("details"),'_label->"ProductDetails")


Remember,theproductformcomesfromtheproductcontroller.Forthehelper,wejustneedtotellitwhichproductfieldisforwhichHTMLlabel,andthat'sit.ThiswillproducethefollowingUIs.

ThefollowingimageshowstheblankproductindexUI:

TheinsertUIformforproductdetailslooksasfollows:

Withproductsadded,theproductindexUIappearsasfollows:

Nowwecanmovetoreviews.Let'sgofortheUIs.

ThereviewindexUIinreview_index.scala.htmlisasfollows:

@(reviews:Seq[Review])(implicitflash:Flash)

@main("Reviews"){

@if(!reviews.isEmpty){


<tr>

<th>ProductId</th>

<th>Author</th>

<th>Comment</th>

<th></th>

</tr>

@for(review<-reviews){

<tr>

<td><ahref="@routes.ReviewController.details

(review.id.get)">@review.productId</a></td>

<td>@review.author</td>

<td>@review.comment</td>

<td>

<formmethod="post"action="@routes.ReviewController.

remove(review.id.get)">

<buttonclass="btnbtn-link"type="submit"><iclass=

"icon-trash"></i>Delete</button>

</form></td>

</tr>

}

</table>

}

<p><ahref="@routes.ReviewController.blank"class="btnbtn-

success"><iclass="icon-plusicon-white"></i>AddReview</a></p>

}

Soherewehavethesamethingsaswehadfortheproducts.Let'stakealookatthedetailspageforreviewnow.Youcanfinditinreview_details.scala.html.

@(id:Option[Long],review:Form[Review],products:

Seq[(String,String)])(implicitflash:Flash)



@main("review:"+review("name").value.getOrElse("")){

@if(review.hasErrors){






</div>

}


routes.ReviewController.update(id.get)else

routes.ReviewController.insert){

@helper.select(

field=review("productId"),

options=products,

'_label->"ProductName",

'_default->review("productId").value.getOrElse("Choose

One"))

@helper.inputText(review("author"),'_label->"Author")

@helper.inputText(review("comment"),'_label->

"Comment")



@if(id.isDefined){Updatereview}else{Newreview}

</button>

</div>

}

}

Here,inthislastcode,wehavealmosteverythingsimilartowhatwehadforproducts,however,thereisonebigdifference.ReviewneedstobeassociatedwithaproductID.That'swhy,weneedtohaveaselectfortheproducts,whichisfulfilledbyproducts:Seq[(String,String)].ThiscomesfromtheReviewControllercode.ThiscodeproducesthefollowingUIs.

TheblankreviewindexUIisshownasfollows:

TheinsertreviewdetailsUIlooksasfollows:

ThereviewindexUIwithreviewswilllooklikethefollowingimage:

Nowwecanmovetothelastone:theimageUI.TheimageUIisverysimilartothereviewUI,becauseitdependsontheproductIDtoo.Let'sgoforit.

TheimageindexUIhasthefollowingcodeinimage_index.scala.html:

@(images:Seq[Image])(implicitflash:Flash)

@main("Images"){

@if(!images.isEmpty){


<tr>

<th>ProductID</th>

<th>URL</th>

<th></th>

</tr>

@for(image<-images){

<tr>

<td><ahref="@routes.ImageController.details

(image.id.get)">@image.id</a></td>

<td>@image.productId</td>

<td>@image.url</td>


"@routes.ImageController.remove(image.id.get)">

<buttonclass="btnbtn-link"type="submit">

<iclass="icon-trash"></i>Delete</button>

</form></td>

</tr>

}

</table>

}

<p><ahref="@routes.ImageController.blank"class=

"btnbtn-success"><iclass="icon-plusicon-white">

</i>AddImage</a></p>

}

ImageDetailsUI[image_details.scala.html]

@(id:Option[Long],image:Form[Image],products:Seq[(String,String)])

(implicitflash:Flash)



@main("Image:"+image("productId").value.getOrElse("")){

@if(image.hasErrors){




Sorry!Someinformationdoesnotlookright.Couldyouimage

itpleaseandre-submit?

</div>

}


routes.ImageController.update(id.get)else

routes.ImageController.insert){

@helper.select(field=image("productId"),

options=products,

'_label->"ProductName",

'_default->image("productId").value.getOrElse("Choose

One")

)

@helper.inputText(

image("url"),

'_label->"URL",

'_placeholder->"/assets/images/default_product.png",

'onchange->"javascript:loadImage();"

)

Visualization<br>

<imgid="imgProduct"height="42"width="42"

src="@image("url").value"></img>



@if(id.isDefined){UpdateImage}else{NewImage}

</button>

</div>

}

}

ThisUItemplatewillcreatethefollowingHTMLPages:

TheblankimageindexUIisshowninthefollowingimage:

TheinsertUIforimagedetailslooksasfollows:

ThefollowingistheimageindexUIwithitems:

NowwehaveacompleteworkingUIapplication.Therearecontrollers,models,views,andsimpleservicesaswell.Wealsohaveallvalidationsinplace.

SummaryInthischapter,youlearnedhowtocreatecontrollers,models,services,views(usingTwirltemplating),Guiceinjections,androuting.WecoveredtheprinciplesofScalaWebDevelopmentusingthePlayframework.Bytheendofthechapter,wegottheapplicationwiththePlayframeworkupandrunning.

Inthenextchapter,wewilllearnmoreaboutservices.Asyoumayrealize,wedidsomesimpleservicesinthischapterforproducts,reviews,andimages,butnowwewillcontinueworkingwithservices.

Chapter4.DevelopingReactiveBackingServicesInthepreviouschapter,youlearnedhowtoBootstrapyourapplicationusingActivator,andwedevelopedourwebapplicationusingScalaandthePlayframework.NowwewillenterintothereactiveworldofRxJavaandRxScala.


ReactiveprogrammingprinciplesandtheReactiveManifestoUnderstandingtheimportanceofnon-blockingIOObservables,functions,anderrorhandlingwithRxRefactoringourcontrollersandmodelstocallourservicesAddingRxScalatoourservicesAddinglogging

GettingstartedwithreactiveprogrammingBuildingapplicationstodayisharderthanitwasbefore.Everythingnowismorecomplex:wehavetousemorecoresinprocessors,andwehavecloud-nativeapplicationswithhundredsofmachinesforasingleservice.Concurrentprogramminghasalwaysbeenhard,anditwillalwaysbeso,becauseitisdifficulttomodeltime.Inordertoaddressthis,weneedtohaveareactivestyleofarchitecture.Inordertobeabletohandlemoreusersandscaleourapplications,weneedtoleverageAsyncandnon-blockingIO.Tohelpuswiththistask,wecanrelyonRxJavaandRxScala.Beingreactiveisnotonlyaboutcodebutalsoaboutarchitecturalprinciples.

TheReactiveManifestocapturestheseprinciplesverywell,andthereareacoupleoftechnologiesthatfollowtheseprinciplesinordertobefullyreactive.

TheReactiveManifestocanbeshownasinthefollowingdiagram:

Formoreinformation,youcanvisithttp://www.reactivemanifesto.org/.

TheReactiveManifestodescribeswhatthisreactivearchitecture/systemlookslike.Basically,therearethefollowingfourcoreprinciplesunderliningthereactiveidea:

Responsive:Thesystemshouldrespondinatimelymanner.Inotherwords,thesystemshoulddetectproblemsquickly,anddealwiththemeffectively,apartfromprovidingrapidandconsistentresponsetime.Resilient:Thesystemshouldstayresponsiveevenafterfailure.Thisisdoneviareplicationcontainment,isolation,anddelegation(https://en.wikipedia.org/wiki/Delegation_pattern).Containmentandisolationareideasthatcomefromthenavalindustry,andaredefinedbythebulkheadpattern(https://en.wikipedia.org/wiki/Bulkhead_(partition)).Failuresarecontainedateachcomponent.Doingsomakessurethatonesystem'sfailuredoesnotaffectothersystems.Recoveryisdelegatedtoanothersystem,andnottotheclient.

http://www.reactivemanifesto.org/

https://en.wikipedia.org/wiki/Delegation_pattern

https://en.wikipedia.org/wiki/Bulkhead_(partition)

Elastic:Theabilitytoincreaseanddecreaseresourcesforthesystem.ThisrequiresyoudesignyoursystemwithoutSinglePointOfFailure(SPOF),anddesignusingshardsandreplication.Reactivesystemsarepredictiveandcost-effective.Message-driven:Reactivesystemsrelyonasynchronousmessagepassingtoensureloosecoupling,isolation,andlocationtransparency.Bydoingso,wecandelegatefailuresasmessages.Thisgivesuselasticity,loadmanagement,andflowcontrol.It'sevenpossibletoapplyback-pressure(alsoknownasthrottling)whenneeded.Allthisshouldbedonewithnon-blockingcommunicationforbetterresourceutilization.

Alright,let'susetheseprinciplespracticallyinourapplicationwithRxScala.RxScalaisjustaScalawrapperforRxJava,butitisbettertousebecauseitmakesthecodemorefunctional,andyoudon'tneedtocreateobjectssuchasAction1.

Inourapplication,wehavethreemajorresources:products,reviews,andimages.Allproductsmusthaveaprice,sowewillbuiltafullyreactivepricegeneratorwiththePlayframework,RxScala,andScalarightnow.

Sofirstofall,wewillplaywithRxScalainourPlayapplication,thenwewillcreateaseparatemicroservice,makereactivecallstothatmicroservice,andretrieveourpricesuggestionforthatservice.Alldataflowtransformationsareusingobservables.

Let'screatetheroutesforthiscontrolleratReactiveWebStore/conf/routes,asfollows:

#

#Services

#

GET/rx/pricescontrollers.RxController.prices

GET/rx/apricescontrollers.RxController.pricesAsync

Wehavetworouteshere:oneforaregularaction,andanotherforanAsyncactionthatwillreturnaScalaFuture.Let'screateanewcontrollercalledRxController.scala.ThiscontrollerneedstobelocatedatReactiveWebStore/app/controller.

Let'shavealookatRxController,whichisourreactiveRxScalasimplecontroller:

@Singleton

classRxController@Inject()(priceService:IPriceSerice)extends

Controller{

defprices=Action{implicitrequest=>

Logger.info("RXcalled.")

importExecutionContext.Implicits.global

valsourceObservable=priceService.generatePrices

valrxResult=Observable.create{sourceObservable.subscribe

}

.subscribeOn(IOScheduler())

.take(1)

.flatMap{x=>println(x);Observable.just(x)}

.toBlocking

.first

Ok("RxScalaPricesuggestedis="+rxResult)

}

defpricesAsync=Action.async{implicitrequest=>

Logger.info("RXAsynccalled.")

importplay.api.libs.concurrent.Execution.Implicits.

defaultContext

valsourceObservable=priceService.generatePrices

valrxResult=Observable.create{sourceObservable.subscribe

}


.take(1)

.flatMap{x=>println(x);Observable.just(x)}

.toBlocking

.first

Future{Ok("RxScalaPricesugestedis="+rxResult)}

}

}

So,intheveryfirstmethodcalledprices,wereturnaregularPlayframeworkAction.WereceiveIPriceServiceviadependencyinjection.ThisIPriceServiceisareactiveservice,becauseitusesobservables.Sowecallamethod,generatePrices,whichwillreturnObservable[Double].Thiswillbeoursourceobservable,thatis,thedatasourceofourcomputation.Movingforward,wecreateanewobservablesubscribingintothesourceobservable,andthenweapplysometransformation.Forinstance,wetakejustoneelement,andthenwecanperformtransformationusingflatMap.Forthiscase,wedonotreallyapplytransformations.WeuseflatMaptosimplyprintwhatwegot,andthencontinuethechain.ThenextstepistocalltoBlocking,whichwillblockthethreaduntilthedataisback.Oncethedataisback,wegetthefirstelement,whichwillbeadouble,andwereturnOk.

Blockingsoundsbadandwedon'twantthat.Alternatively,wecanusetheasynccontrollerinthePlayframework,whichwon'tblockthethreadandreturnaFuture.Sothat'sthesecondmethod,calledpricesAsync.Herewehavesimilarobservablecode.However,intheend,wereturnaFuturewhichisnotblocking.However,wecalltoBlockingfromtheobservablethatwillblockthecall,thusmakingitthesameasthepreviousmethod.Tobeclear,Actionisnotbad.Bydefault,everythingisAsyncinPlay,becauseevenifyoudon'treturnanexplicitFuture,thePlayframeworkcreatesapromiseforyandmakesyoucodeAsync.UsingHTTP,youwillblockthethreadatsomepoint.Ifyouwanttobe100%non-blockingfromendtoend,youneedtoconsideradifferentprotocolsuchaswebsockets.

Let'stakealookattheservicenow.Thisservice,andotherservices,needtobelocatedatReactiveWebStore/apps/services.Firstwewillcreatetraittodefinetheservicebehavior.

IPriceService-ScalatraitAsyoucanseeinthefollowingcode,wedefinedIPriceServicewithjustoneoperation,thatis,generatePrices,whichreturnsObservable[Double].Thenextstepnowistodefinetheserviceimplementation.Thiscodeneedstobelocatedinthesameservicesfolderastheprevioustrait:

traitIPriceSerice{

defgeneratePrices:Observable[Double]

}

PriceService-RxScalaPriceServiceimplementationFirstwecreatePublishSubject,whichisawaytogeneratedataintoobservables.ScalahasanicewayofgeneratinginfinitesequencesusingStream.continually.Sowepassafunctionwhichgeneratesdoublerandomnumbersfrom0to1,000.Thiswillhappenforeverand,becausethisisanexpensivecomputation,werunitintoaFuture.TherightthingtodowillbetouseamethodafterStream,becausethiswillfinishthecomputation.Forthesakeoftheexercise,wewillkeepitthiswayfornow.

EachdoublerandomnumberispublishedintoPublishSubjectbytheonNextmethod.Nowlet'smovetothegeneratePricesmethod,whichusesthreeobservablestogeneratethenumberforus.Tobeclear,ofcoursewecoulddoasimplersolutionhere.However,wearedoingitthiswaytoillustratethepowerofobservables,andhowyoucanusetheminpractice.

WehaveEvenandOddobservables,bothsubscribingtoPublishSubject,sotheywillreceiveinfinitedoublenumbers.ThereisaflatMapoperationtoadd10tothenumber.Keepinmindthateverythingyoudoneedstobeinanobservable.SowhenyoudotransformationswithflatMap,youalwaysneedtoreturnanobservable.

Finally,weapplythefilterfunctiontogetonlyevennumbersontheEvenobservableandonlyoddnumbersontheOddobservable.Allthishappensinparallel.EvenandOddobservablesdonotwaitforeachother.

Thenextstepistomergebothobservables.WecreateathirdobservablethatstartsemptyandthenmergestheinfinitedoublesfromtheEvenobservablewiththeinfinitedoublesfromtheOddobservable.Nowisthetimetolimitthecomputationtoonly10numbers.Wedon'tknowhowmanyoddorhowmanyevennumberswillbetherebecauseofAsync.Ifyouwishtocontrolthenumberofoddsandevens,youneedtoapplythetakefunctiononeachobservable.

Finally,weapplyfoldLefttosumallthenumbersandgetatotal.However,whenwedothat,wegetonly90%ofthenumbers.Thislastobservableiswhatisreturnedtothecontroller.Nothingisblockedhere,andit'sallAsyncandreactive.

YoumaybewonderingwhyStream.Continuouslygeneratesdifferentvaluesallthetime.ThathappensbecauseweuseaCall-by-NamefunctioninScala.WeimportthenextDoublefunction,andpassafunctioninsteadofthevalueofthefunction:

@Singleton

classPriceServiceextendsIPriceSerice{

vardoubleInfiniteStreamSubject=PublishSubject.apply[Double]()

Future{

Stream.continually(nextDouble*1000.0).foreach{

x=>Thread.sleep(1000);

doubleInfiniteStreamSubject.onNext(x)

}

}

overridedefgeneratePrices:Observable[Double]={

varobservableEven=Observable.create{

doubleInfiniteStreamSubject.subscribe}


.flatMap{x=>Observable.from(Iterable.fill(1)(x+10))

}

.filter{x=>x.toInt%2==0}

varobservableOdd=Observable.create{



.flatMap{x=>Observable.from(Iterable.fill(1)(x+10))

}

.filter{x=>x.toInt%2!=0}

varmergeObservable=Observable

.empty


.merge(observableEven)

.merge(observableOdd)

.take(10)

.foldLeft(0.0)(_+_)

.flatMap{x=>Observable.just(x-(x*0.9))}

returnmergeObservable

}

}

WeneedtoregisterthisserviceinGuiceinModule.scalalocatedinthedefaultpackageatReactiveWebStore/app.

GuiceInjection-Module.scalaYourModule.scalafileshouldlooksomethinglikethis:





//AskGuicetocreateaninstanceofApplicationTimerwhen

//the

//applicationstarts.



asEagerSingleton()


asEagerSingleton()


asEagerSingleton()

bind(classOf[IPriceSerice]).to(classOf[PriceService]).

asEagerSingleton()

}

}

Inordertocompileandruntheprecedingcode,weneedtoaddanextraSBTdependency.Openbuild.sbt,andaddRxScala.Wewillalsoaddanotherdependency,whichisws,aplaylibrarytomakewebservicecalls.Wewilluseitlaterinthischapter.

Yourbuild.sbtshouldlooksomethinglikethis:

name:="""ReactiveWebStore"""

version:="1.0-SNAPSHOT"

lazyvalroot=(projectinfile(".")).enablePlugins(PlayScala)


libraryDependencies++=Seq(

jdbc,

cache,

ws,

"org.scalatestplus.play"%%"scalatestplus-play"%"1.5.1"%

Test,

"com.netflix.rxjava"%"rxjava-scala"%"0.20.7"

)

resolvers+="scalaz-bintray"at

"http://dl.bintray.com/scalaz/releases"

resolvers+=DefaultMavenRepository

Nowwecancompileandrunthiscodeusingactivatorrun.

WecancallthisnewroutenowusingaCURLcall.Ifyouprefer,youcanjustopenyourbrowseranddoitthere.

curl-vhttp://localhost:9000/rx/prices

curl-vhttp://localhost:9000/rx/aprices

Wewillseethefollowingresult:

Great!WehaveRxScalaworkingwiththePlayframework.Nowwewillrefactorourcodetomakeitevenmoreinteresting.SowewillcreateamicroserviceusingthePlayframework,andwewillexternalizethisrandomnumbergeneratortothemicroservice.

WeneedtocreateanewPlayframeworkapplication.Wewillpicktheoptionnumber6)play-scalaapplicationtemplate.Openyourconsole,andthentypethefollowingcommand:

$activatornewng-microservice

Youwillseethisresult:

Let'screatetheroutesonng-microservice.Wewon'thaveanyUIhere,sincethiswillbeamicroservice.Weneedtoaddarouteatng-microservice/conf/routes:

#Routes

#Thisfiledefinesallapplicationroutes(Higherpriorityroutes

first)

#~~~~

GET/doublecontrollers.NGServiceEndpoint.double

GET/doubles/:ncontrollers.NGServiceEndpoint.doubles(n:Int)

Nowlet'sdefinethecontroller.Thisisnotaregularcontroller,becausethisonewon'tserveUIviews.Instead,itwillserveJSONtothemicroserviceconsumers.Herewewillhavejustoneconsumer,whichwillbeReactiveWebStore.However,itispossibletohaveasmany

consumersasyouwishsuchasothermicroservicesorevenmobileapplications.

NGServiceEndpointForthiscontroller,wejusthavetworoutes.Theroutesaredoubleanddoubles.Thefirstroutereturnsadoublefromtheservice,andthesecondonereturnsalistofdoublesgeneratedinabatch.Forthesecondmethod,wegetalistofdoublesandtransformthatlistinJSONusingthePlayframeworkutilitylibrarycalledJson:

classNGServiceEndpoint@Inject()(service:NGContract)extends

Controller{

defdouble=Action{

Ok(service.generateDouble.toString())

}

defdoubles(n:Int)=Action{

valjson=Json.toJson(service.generateDoubleBatch(n))

Ok(json)

}

}

Thenextstepiscreatetraitforthemicroservice.ThistraitisalsotheservicecontractinServiceOrientedArchitecture(SOA)terms,thatis,thecapabilitiesthatthemicroserviceoffers.

TheNGContract.scalafileshouldlooksomethinglikethis:

traitNGContract{

defgenerateDouble:Double

defgenerateDoubleBatch(n:Int):List[Double]

}

Let'slookattheServiceimplementationofthismicroservice:

packageservices

importscala.util.Random

importscala.util.Random.nextDouble

classNGServiceImplextendsNGContract{

overridedefgenerateDouble:Double={

Stream.continually(nextDouble*1000.0)

.take(1)

}

overridedefgenerateDoubleBatch(n:Int):List[Double]={

require(n>=1,"Numbermustbebiggerthan0")

valnTimes:Option[Int]=Option(n)

nTimesmatch{

caseSome(number:Int)=>

Stream.continually(nextDouble*1000.0)

.take(n)

.toList

caseNone=>

thrownewIllegalArgumentException("Youneedprovideavalid

numberofdoublesyouwant.")

}

}

}

ThisserviceimplementationdoesnothaveanyRxScalacode.However,itisveryfunctional.Wehavetwomethodsimplementedhere.ThemethodsaregenerateDoubleandgenerateDoubleBatch,whichreceive,throughparameters,thenumberofdoublesyouwantittogenerateforyou.Forthefirstoperation(generateDouble),weuseStream.continuallytogenerateinfiniterandomdoubles,thenwemultiplythesenumbersby1,000,andthentakejust1andreturnit.

Thesecondoperationisverysimilar.However,wehavetoaddsomevalidationstomakesurethatthenumbersofdoublearepresent.Thereareacoupleofwaystodoit.OnewayusetheassertmethodinScala.Thesecondwayisthepatternmatcher,whichisnicebecausewedon'tneedtowriteanifstatement.

ThistechniqueisverycommonintheScalacommunity.Sowecreateanoptionthattakesthenumber,andthenwepattern-matchit.Ifthereisanumberpresent,thecaseSomemethodwillbetriggered,otherwise,thecaseNonewillbecalled.

Afterthesevalidations,wecanuseStreamtogenerateasmanynumbersasrequested.Beforewerunthecode,weneedtodefinetheGuiceinjections.Thisfileislocatedinthedefaultpackageatng-microservice/app/:





bind(classOf[NGContract]).to(classOf[NGServiceImpl]).

asEagerSingleton()

}

}

Nowitstimetocompileandrunourmicroservice.SincewealreadyhaveaplayapplicationcalledReactiveWebStorerunningonport9000,youwillhavetroubleifyousimplyrunthemicroservice.Tofixthis,weneedtorunitonadifferentport.Let'suse9090forthemicroservice.Opentheconsole,andexecutethecommand$activatorfollowedby$run9090:

ng-microservice$activator-Dsbt.task.forcegc=false


[info]Loadingprojectdefinitionfrom


ations/Chap4/ng-microservice/project

[info]Setcurrentprojecttong-microservice(inbuild

file:/home/diego/github/diegopacheco/Book_Building_Reactive_Functional_Scala_A

pplications/Chap4/ng-microservice/)

[ng-microservice]$run9090

---(Runningtheapplication,auto-reloadingisenabled)---

[info]p.c.s.NettyServer-ListeningforHTTPon/0:0:0:0:0:0:0:0:9090

(Serverstarted,useCtrl+Dtostopandgobacktotheconsole...)

Wecantestourmicroservicebycallingthetwooperationsthatwehave.Solet'sopenthewebbrowseranddoit.

Thedoublemicroservicecallathttp://localhost:9090/doublelooksasfollows:

Everytimeyoucallthisoperation,you'llseeadifferentrandomdoublenumber.Nowwecantryoutthenextoperation:theoneyoupassforthenumberofdoublesyouwant.ThisoperationwillreturnalistofdoublesintheJSONformat.

Thecallfordoubleinbatchesmicroserviceathttp://localhost:9090/doubles/100lookslikethefollowingscreenshot:

Itworks!Wehave100doubleshere.Nowthatwehaveamicroserviceworking,wecangobacktoourReactiveWebStoreandchangeourRxScalacode.Wewillcreatenewcontrollers.Wewillalsoupdatetheexistingcodeforproductstocallournewcode,andsuggestapricefortheuserontheUI,allinareactivemanner.Keepinmindthatyouneedtohaveng-microservicerunning;otherwise,ReactiveWebStorewon'tbeabletoretrievedoubles.

PlayframeworkandhighCPUusageIfyounoticeyourCPUusagegoinghigherthanitshould,donotworry;thereisafixforit.Actually,theissueisrelatedtoSBT.Justmakesurethat,whenyourunActivator,youpassthefollowingparameter:

$activator-Dsbt.task.forcegc=false.

GoingbacktoReactiveWebStore,let'screatenewroutes.OpenReactiveWebStore/conf/routes:

GET/rnd/double

controllers.RndDoubleGeneratorController.rndDouble

GET/rnd/callcontrollers.RndDoubleGeneratorController.rndCall

GET/rnd/rxcontrollers.RndDoubleGeneratorController.rxCall

GET/rnd/rxbat

controllers.RndDoubleGeneratorController.rxScalaCallBatch

Oncewehavethenewroutes,weneedtocreatethenewcontroller.ThiscontrollerneedstobelocatedwiththeothercontrollersatReactiveWebStore/app/controllers.

RndDoubleGeneratorControllerTheRndDoubleGeneratorControllerclassfileshouldlooklikethis:

@Singleton

classRndDoubleGeneratorController@Inject()(service:IRndService)

extendsController{

importplay.api.libs.concurrent.Execution.

Implicits.defaultContext

defrndDouble=Action{implicitrequest=>

Ok(service.next().toString())

}

defrndCall=Action.async{implicitrequest=>

service.call().map{res=>Ok(res)}

}

defrxCall=Action{implicitrequest=>

Ok(service.rxScalaCall().toBlocking.first.toString())

}

defrxScalaCallBatch=Action{implicitrequest=>

Ok(service.rxScalaCallBatch().toBlocking.first.toString())

}

}

AllmethodsintheprecedingcontrollercalltheserviceIRndService.AlloperationsinRndServicecallng-microservice.Herewehavesomeflavorsofoperations,whichwillbecoveredingreatdetailnextwhenweexploretheserviceimplementation.

Therearesomeinterestingthingshere:forinstance,forthesecondoperationcalledrndCall,weseeAction.asyncinuse,whichmeansourcontrollerwillreturnaFuture,andthisFuturecomesfromtheservice.WealsoexecuteaMaptotransformtheresultintoanOk.

ThelastoperationcalledrxScalaCallBatchisthemostinteresting,andtheonewewillbeusingforourUI.However,youcanusetheotheroneifyouwish,sincetheyallreturndoubles,andthat'sgood.

IRndService.scala-ScalatraitLet'slookattheservicedefinition.Firstofall,weneedtodefineatraitfortheservicethatwilldefinetheoperationsweneed:

traitIRndService{

defnext():Double

defcall():Future[String]

defrxScalaCall():Observable[Double]

defrxScalaCallBatch():Observable[Double]

}

RndService.scala-RndServiceimplementationNowwecanmovetotherealserviceimplementation.ThisneedstobelocatedatReactiveWebStore/app/services:

@Singleton

classRndService@Inject()(ws:WSClient)extendsIRndService{


defaultContext

overridedefnext():Double={

valfuture=ws.url("http://localhost:9090/double").get().map

{res=>res.body.toDouble}

Await.result(future,5.seconds)

}

overridedefcall():Future[String]={

ws.url("http://localhost:9090/double").get().map

{res=>res.body}

}

overridedefrxScalaCall():Observable[Double]={

valdoubleFuture:Future[Double]=

ws.url("http://localhost:9090/double").get().map{x=>

x.body.toDouble}

Observable.from(doubleFuture)

}

//Continue...

Inordertocallourmicroservice(ng-microservice),weneedtoinjectaspecialPlayframeworklibrarycalledws,autilitylibrarytocallwebservices.Weinjectitbyaddingthecode(ws:WSClient)intotheclassdefinition.

Whenyoucallsomethingwithws,itreturnsaFuture.WeneedtohavetheFutureexecutorsinplace.That'swhytheimportdefaultContextisveryimportant,andyoucannotskipit.

Forthemethod,asyoucansee,wenextcallourmicroserviceathttp://localhost:9090/doubletogetasingledouble.Wemapthisresult,andgetthebodyoftheresult,whichwillbethedoubleitself.

Forthismethod,weuseAwait.result,whichwillblockandwaitfortheresult.Iftheresultisnotbackinfiveseconds,thiscodewillfail.

Thesecondmethodcalledcalldoesthesame,butthemaindifferenceisthatwearenotblockingtheservice;instead,wearereturningaFuturetothecontroller.

Finally,thelastmethodcalledrxScalaCalldoesthesame:itcallsourmicroserviceusingthewslibrary.However,wereturnanobservable.ObservablesaregreatbecausetheycanusedasaFuture.

Nowitistimetogocheckoutthefinaloperationandthemostinterestingone.Forthissameclass,weneedtoaddanothermethodsuchasthisone:

ThemethodrxScalaCallBatchinRndService.scalaisasfollows:

overridedefrxScalaCallBatch():Observable[Double]={

valdoubleInfiniteStreamSubject=PublishSubject.apply[Double]()

valfuture=ws.url("http://localhost:9090/doubles/10")

.get()

.map{x=>Json.parse(x.body).as[List[Double]]}

future.onComplete{

caseSuccess(l:List[Double])=>l.foreach{e=>

doubleInfiniteStreamSubject.onNext(e)}

caseFailure(e:Exception)=>

doubleInfiniteStreamSubject.onError(e)

}

varobservableEven=Observable.create{


.onErrorReturn{x=>2.0}

.flatMap{x=>Observable.from(Iterable.fill(1)(x+10))}

.filter{x=>x.toInt%2==0}

.flatMap{x=>println("ODD:"+x);Observable.just(x)}

varobservableOdd=Observable.create{


.onErrorReturn{x=>1.0}

.flatMap{x=>Observable.from(Iterable.fill(1)(x+10))}

.filter{x=>x.toInt%2!=0}

.flatMap{x=>println("EVEN:"+x);Observable.just(x)}

varmergeObservable=Observable

.empty

.merge(observableEven)

.merge(observableOdd)

.take(10)

.foldLeft(0.0)(_+_)

.flatMap{x=>Observable.just(x-(x*0.9))}

mergeObservable

}

So,firstwecreatePublishSubjectinordertobeabletoproducedatafortheobservables.Thenwemakethewscalltoourmicroservice.Themaindifferencenowisthatwecallthebatchesoperationandorder10doubles.Thiscodehappensinafuture,soitisnon-blocking.

WethenusetheMapfunctiontotransformtheresult.Theng-microservicefunctionwillreturnJSON,soweneedtodeserializethisJSONintoScalaobjects.Finally,werunapatternmatcherintheFutureresult.Iftheresultisasuccess,itmeanseverythingisgood.So,foreachdouble,wepublishintotheobservablesusingPublishSubject.Iftheserviceisdownorwehaveaproblem,wepublishanerrortotheobservablesdownstream.

Nextwecreatethreeobservables:oneforoddnumbers,oneforevennumbers,andathirdonewhichwillmergetheothertwoanddoextracomputation.ThewaywedidtheconversionbetweenFutureandObservableisideal,becauseitisnon-blocking.

HerewehavecodeverysimilartowhatwehadbeforefortheRxcontroller.Themaindifferenceisthatwehaveerrorhandling,becauseng-microservicemightneverreturn,asitmaybedownorjustnotworking.Soweneedtostartworkingwithfallbacks.Goodfallbacks

arekeytoerrorhandlingforReactiveapplications.Fallbacksshouldbesortofstatic;inotherwords,theyshouldnotfailatall.

Weprovidedtwofallbackmethods:onefortheOddObservableandtheotherfortheEvenObservable.ThesefallbacksaredonebysettingthemethodOnErrorReturn.Sofortheevenone,thefallbackisstaticandthevalueis2,andfortheoddonethevalueis1.Thisisgreat,becauseevenwithfailureourapplicationcontinuestowork.

Youmightrealizewearenotusingthetakefunctionthistime.Sowillthiscoderunforever?No,becauseng-microservicejustreturns10doubles.Finally,wemergetheobservablesintoasingleobservable,addallthenumbers,get90%ofthevalue,andreturnanobservable.

Module.scala-GuiceInjectionsNowhookthisnewserviceinGuice.Let'schangetheGuiceModule.scalalocatedatReactiveWebStore/apps/Module.scala:






asEagerSingleton()


asEagerSingleton()


asEagerSingleton()

bind(classOf[IPriceSerice]).to(classOf[PriceService]).

asEagerSingleton()

bind(classOf[IRndService]).to(classOf[RndService]).

asEagerSingleton()

}}

NextweneedtocreateaJQueryfunctioninJavaScripttocallournewcontroller.ThisfunctionneedstobelocatedatReactiveWebStore/public/javascripts.

Thefollowingisprice.js,theJQueryfunctionthatcallsourcontroller:

/**

*ThisfunctionsloadsthepriceintheHTMLcomponent.

*/

functionloadPrice(doc){

jQuery.get("http://localhost:9000/rnd/rxbat",function(

response){

doc.getElementById("price").value=parseFloat(response)

}).fail(function(e){

alert('Wops!Wewasnotabletocall

http://localhost:9000/rnd/rxba.Error:'+e.statusText);

});

}

WejusthaveasinglefunctioncalledloadPrice,whichreceivesadocument.WeusetheJQuery.getmethodtocallourcontroller,andparsetheresponse,addingtotheHTMLtextboxcalledprice.Ifsomethinggoeswrong,wealerttheuserthatitwasnotpossibletoloadaprice.

main.scala.htmlWeneedtochangeourmain.scalacodelocatedatReactiveWebStore/app/views/main.scala.htmlinordertoimportanewJavaScriptfunction:


<!DOCTYPEhtml>

<htmllang="en">

<head>

<title>@title</title>

<linkrel="shortcuticon"type="image/png"

href="@routes.Assets.at("images/favicon.png")">


href="@routes.Assets.at("stylesheets/main.css")">


href="@routes.Assets.at("stylesheets/bootstrap.min.css")">

<scriptsrc="@routes.Assets.at("javascripts/jquery-

1.9.0.min.js")"type="text/javascript"></script>

<scriptsrc="@routes.Assets.at("javascripts/bootstrap.js")"


<scriptsrc="@routes.Assets.at("javascripts/image.js")"


<scriptsrc="@routes.Assets.at("javascripts/price.js")"


</head>

<body>

<center><ahref='/'><imgheight='42'width='42'

src='@routes.Assets.at("images/rws.png")'></a>

<h3>@title</h3></center>

<divclass="container">

@alert(alertType:String)={

@flash.get(alertType).map{message=>

<divclass="alertalert-@alertType">



@message

</div>

}

}

@alert("error")

@alert("success")

@content

<ahref="/"></a><BR>

<buttontype="submit"class="btnbtn-primary"

onclick="window.location.href='/';">

ReactiveWebStore-Home

</button>

</div>

</body>

</html>

product_details.scala.htmlFinally,weneedtochangeourproductviewinordertoaddabuttontoloadthepricefromthecontroller.Let'schangetheproduct_detailsviewatReactiveWebStore/app/views/product_details.scala.html:




@main("Product:"+product("name").value.getOrElse("")){







</div>

}



routes.ProductController.insert){



Details")



<buttontype="button"class="btnbtn-primary"

onclick="javascript:loadPrice(document);">LoadRnd

Price</button>



</button>

</div>

}

}

Great!NowwehaveabuttonthatloadsthedatafromthecontrollerusingJQuery.YoucanrealizethatthebuttonLoadRndPricehasanonClickproperty,whichcallsourJavaScriptfunction.

Nowyouneedtoopenyourconsoleandtype$activatorruntocompileandrunthechangesaswedidtoReactiveWebStore.

Thiscommandwillgivethefollowingresult:

ReactiveWebStore$activator-Dsbt.task.forcegc=false


[info]Loadingprojectdefinitionfrom


ations/Chap4/ReactiveWebStore/project

[info]SetcurrentprojecttoReactiveWebStore(inbuild

file:/home/diego/github/diegopacheco/Book_Building_Reactive_Functional_Scala_A

pplications/Chap4/ReactiveWebStore/)

[ReactiveWebStore]$run

---(Runningtheapplication,auto-reloadingisenabled)---

[info]p.c.s.NettyServer-ListeningforHTTPon/0:0:0:0:0:0:0:0:9000

(Serverstarted,useCtrl+Dtostopandgobacktotheconsole...)

[info]application-ApplicationTimerdemo:Startingapplicationat2016-07-

03T02:35:54.479Z.

[info]play.api.Play-Applicationstarted(Dev)

Soopenyoubrowserathttp://localhost:9000,andgototheproductpagetoseeourneedfeatureintegratedandworkinglikeacharm.Keepinmindthatyouneedtohaveng-microserviceworkinginanotherconsolewindow;otherwise,ourapplicationwillusestaticfallbacks.

Thenewproductfeaturewillbeshownathttp://localhost:9000/product/addasseeninthefollowingscreenshot:

SoifyouclickontheLoadRndPricebutton,youwillseesomethinglikethis:

Ifyoutakealookattheapplicationlogintheactivatorconsole,youwillseesomethingsimilartothis:

[info]application-ApplicationTimerdemo:Startingapplicationat2016-07-

03T02:35:54.479Z.

[info]play.api.Play-Applicationstarted(Dev)

[info]application-indexcalled.Products:List()

[info]application-blankcalled.

ODD:722.8017048639501

EVEN:863.8229024202085

ODD:380.5549208988492

EVEN:947.6312814830953

ODD:362.2984794191124

ODD:676.978825910585

ODD:752.7412673916701

EVEN:505.3293481709368

EVEN:849.9768444508936

EVEN:99.56583617819769

Alright,that'sit.Wehaveeverythingworking!

SummaryInthischapter,youlearnedthecoreprinciplesofreactiveapplicationguidedbytheReactiveManifesto.YoualsolearnedhowtocreatereactiveapplicationsusingRxScala.Wethenexplainedhowtocallotherinternalandexternalwebservicesusingthewslibrary.ThenyoulearnedtoserializeanddeserializeJSONusingtheJsonLibrary.Movingon,youlearnedhowtocreatesimplemicroservicesusingthePlayframeworksupport.

Inthenextchapter,wewillcontinuebuildingourapplication,andlearnhowtotestourapplicationwithJUnitandScalaTest.

Chapter5.TestingYourApplicationInthechapterssofar,webootstrappedourapplicationusingActivator,developedourwebapplicationusingScalaandthePlayframework,andaddedaReactivemicroservicecallusingRxScalafordataflowcomputations.NowwewillgoaheadandentertheunittestandcontrollertestingusingtheBDDandPlayframework.


UnittestingprinciplesTestingScalaapplicationswithJUnitBehavior-drivendevelopmentprinciplesTestingwithScalaTestTestingPlayframeworkapplicationswithScalaTestRunningtestsinActivator/SBT

TheneedfortestingTestisafundamentalandveryimportantpartofsoftwaredevelopment.Withouttests,wecannotbesurethatourcodeworks.Weshouldperformtestsonalmostallthecodeweproduce.Therearethingsthatdon'tmakesensefortesting,forinstance,caseclassesandclassesthatjustrepresentstructuralobjects,or,inotherwords,classeswithoutfunctions.Ifyouhavecodethatappliescomputations,transformations,andvalidations,youdefinitelywanttotestthiscodewithagoodcodecoverage,whichreferstofeaturesoranyimportantcodethatisnotjuststructural.

Testcoverageisimportant,becauseitallowsustodorefactoring(improveapplicationcodequalitybyreducingcode,creatinggenericcode,orevendeletingcode)withtrust.Thisisbecause,ifyouhavetestsandifyoudosomethingwrongbyaccident,yourtestswillletyouknow.Thisisallabouthavingshortcyclesoffeedback.Theearlierthebetter;youwanttoknowifyouhaveintroducedbugsassoon,andasclosetodevelopment,aspossible.Nobodylikestodiscoverbugsthatcouldbecaughtbyasimpletestinproduction.

UnittestingprinciplesUnittestingisthesmallestunitoftestingthatyoucouldpossiblyapply.Youneedtoapplyitattheclasslevel.Soaunittestwillcoveryourclasswithallthefunctionsyouhavethere.Butholdonaminute,aclassoftenhasdependencies,andthesedependenciesmighthaveotherdependencies,sohowdoyoutestthat?Weneedtohavemocks,simpledumbobjectsthatsimulateotherclasses'behavior.Thisisanimportanttechniquetoisolatecodeandallowunittesting.

MakingcodetestableUnittestingissimple:basically,wecallafunctionbypassingargumentstoit,andthenwechecktheoutputtoseeifitmatchesourexpectations.Thisisalsocalledassertsorassertions.So,unittestingisaboutasserts.Sometimes,yourcodemightnotbetestable.Forinstance,let'ssayyouhaveafunctionthatreturnsaunitandhasnoparameters.Thisisverytoughtotest,becauseitimpliesthatthefunctionisfullofside-effects.IfyourememberwhatwediscussedinChapter1,IntroductiontoFP,Reactive,andScala,thisisagainstFPprinciples.So,ifwehavethiscase,weneedtorefactorthecodetomakethefunctionreturnsomething,andthenwecantestit.

Isolationandself-containedtestsUnittestsshouldbeself-contained,whichmeansthataunittest'sclassesshouldnotdependonanyparticularorderofexecution.Let'ssayyouhaveaunittestclasswithtwotestfunctions.So,eachtestshouldtestjustonefunctionatatime,andbothfunctionsshouldbeabletoruninanyorderwhatsoever.Otherwise,thetestswillbefragileandhardtomaintaininthelongrun.

EffectivenamingEffectivenamingisessential.Thetestfunctionneedstosayexactlywhatthetestdoes.Thisisimportantbecause,whenthetestfails,itiseasiertofigureoutwhatwentwrongandwhy.Followingthesameidea,whenyoudoassertions,youshouldassertjustonethingatatime.ImaginethatyouneedtotestwhetherawebservicereturnsavalidJSON.ThisparticularJSONcouldhavetwofields:firstnameandlastname.So,youwillmakeoneassertforthenameandanotherforthelastname.Thisway,itwillbeeasiertounderstandwhatthetestdoes,andtotroubleshootwhenthetestfails.

LevelsoftestingWhenweruntests,weoftendoitinlayers.Unittestingisthebasiclevel;however,thereareotherlevelssuchascontrollertests,integrationtests,UItests,End-to-Endtests,stresstests,andsomanyothers.Forthisbook,wewillcoverunittests,controllertests,andUItestsusingJunitandScalaTest,Play'sframeworksupport.

TestingwithJunitIfyoucomefromaJavabackground,itishighlypossiblethatyouhavealreadyworkedwithJunit.It'spossibletotestwithJunitusingtheScalaandPlayframework.However,thisisnotthebestpracticewhenwearecreatingapplicationswiththePlayframework,sinceitfavorsBehaviorDrivenDevelopment(BDD)testingwithScalaSpec.Forthischapter,wewillcoverhowtoperformallsortsoftestusingBDDandPlay.Rightnow,let'stakealookathowwecandounittestingwithJunitbeforewemovetoBDD.

@RunWith(classOf[Suite])

@Suite.SuiteClasses(Array(classOf[JunitSimpleTest]))

classJunitSimpleSuiteTest

classJunitSimpleTestextendsPlaySpecwithAssertionsForJUnit{

@TestdeftestBaseService(){

vals=newProductService

valresult=s.findAll()

assertEquals(None,result)

assertTrue(result!=null)

println("AllgoodjunitworksfinewithScalaTestandPlay")

}

}

SowhatwehaveintheprecedingcodeisaclassthatextendsPlaySpec,andaddsatraitcalledAssertionForJunit.Whydon'twehavetheclassicalJunitclasshere?BecausethePlayframeworkissetuptorunScalatests,sothisbridgeallowsustorunJunitbyScalaTestPlayframeworkconstructs.

ThenwehaveatestfunctioncalledtestBaseServer,[email protected],wecreateaninstanceofProductService,andthenwecallthefunctionfindAll.

Finally,wehaveassertionsthatwillcheckiftheresultiswhatweareexpecting.Sowedon'thaveproducts,becausewedidnotinsertthemearlier.Hence,weexpecttohaveNoneastheresponse,andtheresultshouldalsonotbenull.

Youcanrunthisinyourconsoleusingthefollowingcommand:

$activator"test-onlyJunitSimpleTest"

Youwillseetheresultshowninthenextscreenshot:

Asyoucansee,ourtestwasexecutedwithoutanyissues.It'salsopossibletorunthistestandanormaltestinJunitusingtheEclipseIDE.Youjustright-clickonthefileandselectRunAs:ScalaJunitTest;refertothefollowingscreenshot:

Behavior-DrivenDevelopment-BDDBehavior-DrivenDevelopment(BDD)isanagiledevelopmenttechnique,thatfocusesontheengagementbetweendevelopersandnon-technicalpeoplesuchasproductownersfromthebusiness.Theideaisprettysimple:usethesamelanguageasthebusinessusesinordertoextractthereasonwhythecodeyouarebuildingexistsinthefirstplace.BDDendsupminimizingthetranslationbetweentechlanguageandbusinesslanguage,creatingmoresynergyandlessnoisebetweeninformationtechnologyandbusiness.

BDDtestsdescribewhattheapplicationneedstodo,andhowitbehaves.It'sverycommontowritedownthesetestsusingpairprogramingbetweenbusinesspeopleanddevelopers.ScalaTestisaBDDframework.PlayframeworkhasagreatintegrationwithScalaTest.Let'sgetstartedwithScalaTestandPlayrightnow.

MyFirstPlaySpec.scala-FirstBDDwithScalaTestandthePlayframeworkTheMyFirstPlaySpec.scalaclassshouldcontainthefollowingcode:

classMyFirstPlaySpecextendsPlaySpec{

"x+1"must{

"be2ifx=1"in{

valsum=1+1

summustBe2

}

"be0ifx=-1"in{

valsum=-1+1

summustBe0

}

}

}

So,youcreateaclasscalledMyFirstPlaySpec,andweextenditfromPlaySpecinordertogetPlayframeworkScalaTestsupport.Thenwecreatetwofunctionstotestthesumoftwonumbers.Inthefirsttest,1+1shouldbe2,andinthesecond,-1+1shouldbe0.WhenweexecutemustBe,itisthesamethingasdoinganassertinJunit.ThemaindifferencehereisthatthetesthasbehaviorexplicitlyontheSpec.Nowwecanrunthetestbytypingthefollowing:

$activator"test-onlyMyFirstPlaySpec"

Youwillseethefollowingresult:

TestingwithPlayframeworksupportNowwewillcontinuebuildingourapplication.Let'saddBDDtestsinourapplication.Wewillstartdoingtestsforyourservices.WehavetotestProductService,ImageService,andReviewService.

YourProductServiceTestSpec.scalafileshouldcontainthefollowingcode:

classProductServiceTestSpecextendsPlaySpec{

"ProductService"must{

valservice:IProductService=newProductService

"insertaproductproperly"in{

valproduct=newmodels.Product(Some(1),

"Ball","AwesomeBasketball",19.75)

service.insert(product)

}

"updateaproduct"in{

valproduct=newmodels.Product(Some(1),

"BlueBall","AwesomeBlueBasketball",19.99)

service.update(1,product)

}

"notupdatebecausedoesnotexit"in{

intercept[RuntimeException]{

service.update(333,null)

}

}

"findtheproduct1"in{

valproduct=service.findById(1)

product.get.idmustBeSome(1)

product.get.namemustBe"BlueBall"

product.get.detailsmustBe"AwesomeBlueBasketball"

product.get.pricemustBe19.99

}

"findall"in{

valproducts=service.findAll()

products.get.lengthmustBe1

products.get(0).idmustBeSome(1)

products.get(0).namemustBe"BlueBall"

products.get(0).detailsmustBe"AwesomeBlueBasketball"

products.get(0).pricemustBe19.99

}

"findallproducts"in{

valproducts=service.findAllProducts()

products.lengthmustBe1

products(0)._1mustBe"1"

products(0)._2mustBe"BlueBall"

}

"remove1product"in{

valproduct=service.remove(1)

productmustBetrue

valoldProduct=service.findById(1)

oldProductmustBeNone

}

"notremovebecausedoesnotexist"in{


service.remove(-1)

}

}

}

}

Forthistest,wearetestingallpublicfunctionsavailableinProductService.Thetestsareprettystraightforward:wecallaspecificserviceoperation,suchasfindById,andthenwechecktheresulttomakesurethatallthedatathatissupposedtobethereispresent.

Therearescenarioswheretheserviceshouldreturnanexception,forinstance,ifyoutrytoremovesomethingthatdoesnotexist.Ifyoutakealookatthelasttestfunctioncalled"notremovebecausedoesnotexist",weshouldgetanexception.However,thereisabugintheservicecode.Runthetests,andthenyouwillseeit.

ProductService.scala-FIXthecodeissueThat'sthegreatthingabouttests:theyshowissuesinourcodesothatwecanfixthembeforethecodegoestoproductionandaffectstheuserexperience.Tofixthelasttest,weneedtogototheProductServiceclassandfixamethod.Thisishowwefixit:



if(entry==null||entry.equals(None))thrownew

RuntimeException("CouldnotfindProduct:"+id)

}

Allsetnow,everythingisokay.ThePlayframeworksupportstestingforexpectedexceptionsusingtheinterceptfunctiontopasstheexpectedexception,Let'srunthetestintheconsoleusingtheactivatorcommand.

$activator"test-onlyProductServiceTestSpec"

Afterexecutingthiscommand,wegetthefollowing:

ImageServiceTestSpec.scala-ImageServiceTestAlright,NowwecanaddtestsforImageServiceasfollows:

classImageServiceTestSpecextendsPlaySpec{

"ImageService"must{

valservice:IImageService=newImageService

"insertaimageproperly"in{

valimage=newmodels.Image(Some(1),Some(1),

"http://www.google.com.br/myimage")

service.insert(image)

}

"updateaimage"in{

valimage=newmodels.Image(Some(2),Some(1),

"http://www.google.com.br/myimage")

service.update(1,image)

}

"notupdatebecausedoesnotexist"in{



}

}

"findtheimage1"in{

valimage=service.findById(1)

image.get.idmustBeSome(1)

image.get.productIdmustBeSome(1)

image.get.urlmustBe"http://www.google.com.br/myimage"

}

"findall"in{

valreviews=service.findAll()

reviews.get.lengthmustBe1

reviews.get(0).idmustBeSome(1)

reviews.get(0).productIdmustBeSome(1)

reviews.get(0).urlmustBe"http://www.google.com.br/myimage"

}

"remove1image"in{

valimage=service.remove(1)

imagemustBetrue

valoldImage=service.findById(1)

oldImagemustBeNone

}



service.remove(-1)

}

}

}

}

SothesearetheBDDtestsforImageService.Wehavecoveredalltheavailablefunctionsontheservice.LikeintheProductServiceclass,wealsohavetestsforunfortunatescenarioswhereweexpectexceptionstohappen.

Sometimes,weneedtocallmorethanonefunctiontotestaspecificfunctionoraspecifictest

case.Forexample,in"remove1image",wefirstdeleteanimage.Ourtestcasechecksforanimagethatdoesnotexist.Let'srunthetestsontheActivatorconsole.

$activator"test-onlyImageServiceTestSpec"

Thefollowingresultwillbeobtained:

ReviewServiceTestSpec.scala-ReviewServicetestNext,weneedaddtestsforthereviewservice.Herewego.

classReviewServiceTestSpecextendsPlaySpec{

"ReviewService"must{

valservice:IReviewService=newReviewService

"insertareviewproperly"in{

valreview=new

models.Review(Some(1),Some(1),"diegopacheco",

"TestingisCool")

service.insert(review)

}

"updateareview"in{

valreview=newmodels.Review(Some(1),Some(1),

"diegopacheco","TestingsosoCool")

service.update(1,review)

}




}

}

"findthereview1"in{

valreview=service.findById(1)

review.get.idmustBeSome(1)

review.get.authormustBe"diegopacheco"

review.get.commentmustBe"TestingsosoCool"

review.get.productIdmustBeSome(1)

}

"findall"in{

valreviews=service.findAll()



reviews.get(0).authormustBe"diegopacheco"

reviews.get(0).commentmustBe"TestingsosoCool"


}

"remove1review"in{

valreview=service.remove(1)

reviewmustBetrue

valoldReview=service.findById(1)

oldReviewmustBeNone

}



service.remove(-1)

}

}

}

}

Alright,wehavetestsforthereviewservice.Wecanrunthemnow.

$activator"test-onlyReviewServiceTestSpec"

Hereistheoutput:

TestingroutesThePlayframeworkallowsustotestroutesaswell.Thisisgood,becauseasourapplicationgrowsandwerefactorthecode,wecanbe100%surethatourroutesarefunctioning.Routetestingcouldbeeasilyconfusedwithcontrollertesting.Themaindifferenceisthat,withroutingtesting,weshouldtestifweareabletoreachtheroutesandthat'sit.Afterroutetesting,wewillcovercontrollertestingindetail.

RoutesTestingSpec.scala-PlayframeworkroutetestingYourRoutesTestingSpec.scalafileshouldcontainthefollowingcode:

classRoutesTestingSpecextendsPlaySpecwithOneAppPerTest{

"RootController"should{

"routetoindexpage"in{

valresult=route(app,FakeRequest(GET,"/")).get

status(result)mustBeOK

contentType(result)mustBeSome("text/html")

contentAsString(result)mustinclude("WelcometoReactive

WebStore")

}

}

"ProductController"should{


valresult=route(app,FakeRequest(GET,"/product")).get



contentAsString(result)mustinclude("Product")

}

"routetonewproductpage"in{

valresult=route(app,FakeRequest(GET,

"/product/add")).get



contentAsString(result)mustinclude("Product")

}

"routetoproduct1detailspagepage"in{

try{

route(app,FakeRequest(GET,"/product/details/1")).get

}catch{

casee:Exception=>Unit

}

}

}

"ReviewController"should{


valresult=route(app,FakeRequest(GET,"/review")).get



contentAsString(result)mustinclude("Review")

}

"routetonewreviewpage"in{

valresult=route(app,FakeRequest(GET,

"/review/add")).get



contentAsString(result)mustinclude("review")

}

"routetoreview1detailspagepage"in{

try{

route(app,FakeRequest(GET,"/review/details/1")).get

}catch{


}

}

}

"ImageController"should{


valresult=route(app,FakeRequest(GET,"/image")).get



contentAsString(result)mustinclude("Image")

}

"routetonewimagepage"in{

valresult=route(app,FakeRequest

(GET,"/image/add")).get



contentAsString(result)mustinclude("image")

}

"routetoimage1detailspagepage"in{

try{

route(app,FakeRequest(GET,"/image/details/1")).get

}catch{


}

}

}

}

Soherewehavetestsforallourmaincontrollers,whichareroot,product,review,andimage.RootControlleristhecontrollerofthemainpagewhenyouvisithttp://localhost:9000.

ThereisaspecialhelperfunctioncalledrouteinthePlayframework,whichhelpsustotestroutes.ThenweuseFakeRequestpassthepathtotheroute.It'spossibletotestthestatuscodeandcontenttypeofthepagetowhichtherouterroutedourrequest.

Forproduct,image,andreviewcontrollers,youcanseewearetryingtocallanitemthatdoesnotexist.That'swhywehavethetry...catch,becauseweexpecttohaveanexceptionhappeningthere.

$activator"test-onlyRoutesTestingSpec"

Executingthisprecedingcommandproducesthefollowingresult:

ControllertestingWedidunittests,wedidroutetests,andnowisthetimetoaddcontrollertests.Controllertestsaresimilartoroutestests,buttheyarenotthesame.Forinstance,ourcontrolleralwaysrespondtoUIpages,soweexpectedtocreatespecificHTMLpagesbasedoneachmethod.ThePlayframeworkhasintegrationwithSelenium,whichisatestingframeworkforUIs,andacontrollersthatallowsyoutosimulatewebbrowsers,andyoucandoprettymuchthesameasyouwouldbyclickingonthepageslikearealuser.

Solet'sgetstarted.First,wewillstartwithRndDoubleGeneratorControllerTestSpec.

RndDoubleGeneratorControllerTestSpec.scala-RndDoubleGeneratorControllertestsTheRndDoubleGeneratorControllerTestSpec.scalafileshouldcontainthefollowingcode:

classRndDoubleGeneratorControllerTestSpec

extendsPlaySpec

withOneServerPerSuitewithOneBrowserPerSuitewithHtmlUnitFactory

{

valinjector=newGuiceApplicationBuilder()

.injector

valws:WSClient=injector.instanceOf(classOf[WSClient])



"Assumingng-microserviceisdownrxnumbershouldbe"must{

"work"in{

valfuture=ws.url(s"http://localhost:${port}/rnd/rxbat")

.get().map{res=>res.body}

valresponse=Await.result(future,15.seconds)

responsemustBe"2.3000000000000007"

}

}

}

Thisclasshassomeinterestingthings.Forinstance,weinjectWSClientusingGoogleGuicewithGuiceApplicationBuilder.Secondly,weassumethattheng-microservicewecreatedinthepreviouschapterisdown,sowecanpredicttheresponsecomingfromthefallback.

WecallthecontrollerusingWSClient,andthenwemaptheresponsetoreturnthebodycontentasastring.SothiswillbeanAsyncFuture,andinordertogettheresult,weuseAwaittowaitfivesecondsfortheresponsetocomeback.Oncetheresponseisback,wemakesuretheresultis2.3.Iftheresultdoesnotcomebackin15s,thetestwillfail.Runthefollowingcommand:

$activator"test-onlyRndDoubleGeneratorControllerTestSpec"

Nowyouwillseethefollowingresult:

Allright,nowwehaveacontrollertestfullyworkingusingGuiceinjectionsandtheWSClientPlayframeworklibrary.Let'snowmakecontrollertestsfortheproduct,image,andreviewcontrollers.

IntegrationSpec.scalaWecantestourmainpagetocheckifitisokay.Thisisaverysimpletest,andgetsyoureadyforthenexttests.So,herewego.

classIntegrationSpecextendsPlaySpecwithOneServerPerTestwith

OneBrowserPerTestwithHtmlUnitFactory{

"Application"should{

"workfromwithinabrowser"in{

goto("http://localhost:"+port)

pageSourcemustinclude("WelcometoReactiveWebStore")

}

}

}

Thistestisveryeasy.Wejustcallthemainpage,andwecheckifitcontainsthetextWelcometoReactiveWebStore.Let'srunit.

$activator"test-onlyIntegrationSpec"

Theresultafterrunningthistestisshowninthefollowingimage:

ProductControllerTestSpec.scalaNowwewilllookattheproductcontrollertestspec:

classProductControllerTestSpecextendsPlaySpecwith

OneServerPerSuitewithOneBrowserPerSuitewithHtmlUnitFactory{


"insertanewproductshouldbeok"in{

goTo(s"http://localhost:${port}/product/add")

clickonid("name")

enter("BlueBall")

clickonid("details")

enter("BlueBallisaAwesomeandsimpleproduct")

clickonid("price")

enter("17.55")

submit()

}

"detailsfromtheproduct1shouldbeok"in{

goTo(s"http://localhost:${port}/product/details/1")

textField("name").valuemustBe"BlueBall"

textField("details").valuemustBe"BlueBallisaAwesome

andsimpleproduct"

textField("price").valuemustBe"17.55"

}

"updateproduct1shouldbeok"in{


textField("name").value="BlueBall2"

textField("details").value="BlueBallisaAwesomeand

simpleproduct2"

textField("price").value="17.66"

submit()


textField("name").valuemustBe"BlueBall2"


andsimpleproduct2"


}

"deleteaproductshouldbeok"in{


clickonid("name")

enter("BlueBall")



clickonid("price")

enter("17.55")

submit()

goTo(s"http://localhost:${port}/product")

clickonid("btnDelete")

}

}

}

So,fortheproductcontroller,wesimulateawebbrowserusingSeleniumPlay'sframeworksupport.Wetestbasiccontrollerfunctionalitysuchasinsertinganewproduct,detailsfora

specificproduct,andupdatingandremovingaproduct.

Forinsert,wegotothenewproductformusinggoTo.Weuse$portasavariable.WedothisbecausethePlayframeworkwillbootuptheapplicationforus,butwedon'tknowinwhichport.Soweneedtousethisvariableinordertogettotheproductcontroller.

Thenweclickoneachtextfieldusingtheclickfunction,andweentervaluesusingtheenterfunction.Afterfillinginthewholeform,wesubmititusingthesubmitfunction.

Fordetails,wejustgototheproductdetailspage,andwecheckifthetextfieldshavethevaluesthatweareexpecting.WedothatusingthetextField.valuefunction.

Inordertochecktheproductupdatefunction,weneedtofirstupdatetheproductdefinition,andthengotodetailstoseeifthevalueswechangedarethere.

Finally,wetestthedeletefunction.Forthisfunction,weneedtoclickonabutton.WeneedtosettheIDofthebuttoninordertohavethisworking.WeneedtodoasmallrefactoringinourUItohavetheIDthere.

product_index.scala.htmlYourproduct_index.scala.htmlfileshouldcontainthefollowingcode:


@main("Products"){

@if(!products.isEmpty){


<tr>

<th>Name</th>

<th>Details</th>

<th>Price</th>

<th></th>

</tr>

@for(product<-products){

<tr>

<td><ahref="@routes.ProductController.details

(product.id.get)">@product.name</a></td>

<td>@product.details</td>

<td>@product.price</td>


"@routes.ProductController.remove(product.id.get)">

<buttonid="btnDelete"name="btnDelete"class="btn

btn-link"type="submit"><iclass="icon-

trash"></i>Delete</button>

</form></td>

</tr>

}

</table>

}

<p><ahref="@routes.ProductController.blank"

class="btnbtn-success"><iclass="icon-plusicon-white">

</i>AddProduct</a></p>

}

Allset.NowwecanrunourtestsonActivatorsusingtheconsole.

$activator"test-onlyProductControllerTestSpec"

Thisprecedingcommandshowstheresultinthefollowingscreenshot:

Sincethistestrunstheapplicationforrealandcallsthecontrollersimulatingthewebbrowser,thistestcouldtakesometime.Nowit'stimetomovetotheImageControllertests.

ImageControllerTestSpec.scalaYourproduct_index.scala.htmlshouldcontainthefollowingcode:

classImageControllerTestSpecextendsPlaySpecwithOneServerPerSuitewith

OneBrowserPerSuitewith

HtmlUnitFactory{


"insertanewimageshouldbeok"in{


clickonid("name")

enter("BlueBall")



clickonid("price")

enter("17.55")

submit()

goTo(s"http://localhost:${port}/image/add")

singleSel("productId").value="1"

clickonid("url")

enter("http://myimage.com/img.jpg")

submit()

}

"detailsfromtheimage1shouldbeok"in{

goTo(s"http://localhost:${port}/image/details/1")

textField("url").valuemustBe"http://myimage.com/img.jpg"

}

"updateimage1shouldbeok"in{


textField("url").value="http://myimage.com/img2.jpg"

submit()


textField("url").valuemustBe"http://myimage.com/img2.jpg"

}

"deleteaimageshouldbeok"in{



clickonid("url")

enter("http://myimage.com/img.jpg")

submit()

goTo(s"http://localhost:${port}/image")


}

}

}

Firstofall,weneedtogototheproductcontrollertoinsertaproduct;otherwise,wecannotdoimageoperations,sincetheyallneedaproductID.

image_index.scala.htmlYourimage_index.scala.htmlfileshouldcontainthefollowingcode:


@main("Images"){

@if(!images.isEmpty){


<tr>

<th>ProductID</th>

<th>URL</th>

<th></th>

</tr>

@for(image<-images){

<tr>

<td><ahref="@routes.ImageController.details

(image.id.get)">@image.id</a></td>

<td>@image.productId</td>

<td>@image.url</td>


"@routes.ImageController.remove(image.id.get)">

<buttonid="btnDelete"name="btnDelete"class="btn

btn-link"type="submit"><iclass="icon-

trash"></i>Delete</button></form>

</td>

</tr>

}

</table>

}

<p><ahref="@routes.ImageController.blank"

class="btnbtn-success"><iclass="icon-plusicon-white">

</i>AddImage</a></p>

}

Allset.NowwecanruntheImageControllertests.

$activator"test-onlyImageControllerTestSpec"

Theresultisshowninthefollowingscreenshot:

ImageControllerhaspassedallitstests.NowwewillmovetotheReviewControllertests.

ReviewControllerTestSpec.scalaYourReviewControllerTestSpec.scalafileshouldcontainthefollowingcode:

classReviewControllerTestSpecextendsPlaySpecwithOneServerPerSuitewith

OneBrowserPerSuite

withHtmlUnitFactory{


"insertanewreviewshouldbeok"in{


clickonid("name")

enter("BlueBall")



clickonid("price")

enter("17.55")

submit()

goTo(s"http://localhost:${port}/review/add")


clickonid("author")

enter("diegopacheco")

clickonid("comment")

enter("Testsareamazing!")

submit()

}

"detailsfromthereview1shouldbeok"in{

goTo(s"http://localhost:${port}/review/details/1")

textField("author").valuemustBe"diegopacheco"

textField("comment").valuemustBe"Testsareamazing!"

}

"updatereview1shouldbeok"in{


textField("author").value="diegopacheco2"

textField("comment").value="Testsareamazing2!"

submit()


textField("author").valuemustBe"diegopacheco2"

textField("comment").valuemustBe"Testsareamazing2!"

}

"deleteareviewshouldbeok"in{



clickonid("author")




submit()

goTo(s"http://localhost:${port}/review")


}

}

Firstofall,weneedtogototheproductcontrollertoinsertaproduct;otherwise,wecannotdoimageoperations,sincetheyallneedaproductID.

Forinsert,wegotothenewproductformusinggoto.Weuse$portasavariable.WedothisbecausethePlayframeworkwillbootuptheapplicationforus,butwedon'tknowonwhichport,soweneedtousethisvariableinordertogettotheproductcontroller.

Thenweclickoneachtextfieldusingtheclickfunction,andweentervaluesusingtheenterfunction.Afterfillinginthewholeform,wesubmititusingthesubmitfunction.

Fordetails,wejustgototheproductdetailspageandcheckifthetextfieldshavethevaluesthatweexpect.WedothatusingthetextField.valuefunction.

Inordertochecktheproductupdatefunction,weneedtofirstupdatetheproductdefinition,andthengotothedetailstoseeifthevalueswechangedarethere.

Finally,wetestthedeletefunction.Forthisfunction,weneedtoclickonabutton.WeneedtosettheIDofthebuttoninordertohavethisworking.ThenwedoasmallrefactoringinourUItohavetheIDthere.

review_index.scala.htmlYourreview_index.scala.htmlfileshouldcontainthefollowingcode:


@main("Reviews"){

@if(!reviews.isEmpty){


<tr>

<th>ProductId</th>

<th>Author</th>

<th>Comment</th>

<th></th>

</tr>

@for(review<-reviews){

<tr>

<td><ahref="@routes.ReviewController.

details(review.id.get)">@review.productId</a></td>

<td>@review.author</td>

<td>@review.comment</td>

<td>

<formmethod="post"action="@routes.

ReviewController.remove(review.id.get)">

<buttonid="btnDelete"name="btnDelete"

class="btnbtn-link"type="submit"><iclass="icon-

trash"></i>Delete</button>

</form>

</td>

</tr>

}

</table>

}

<p><ahref="@routes.ReviewController.blank"class="btnbtn-

success"><iclass="icon-plusicon-white"></i>AddReview</a></p>

}

Finally,wecanrunthetestsontheconsole.

$activator"test-onlyReviewControllerTestSpec"

Thetestwillshowthefollowingoutput:

Alright,ReviewControllerhaspassedallourtests.

It'saverygoodpracticetohavethetestsseparatedbytype.However,ifyouwant,youcouldmixallthetestssuchasunittesting,controllertesting,androutetestinginonesinglefile.

ApplicationSpec.scalaYourApplicationSpec.scalashouldhavethefollowingcode:

classApplicationSpecextendsPlaySpecwithOneAppPerTest{

"Routes"should{

"send404onabadrequest"in{

route(app,FakeRequest(GET,"/boum")).map(status(_))mustBe

Some(NOT_FOUND)

}

}

"HomeController"should{

"rendertheindexpage"in{

valhome=route(app,FakeRequest(GET,"/")).get

status(home)mustBeOK

contentType(home)mustBeSome("text/html")

contentAsString(home)mustinclude("WelcometoReactiveWeb

Store")

}

}

"RndController"should{

"returnarandomnumber"in{

//Assumingng-microserviceisdownotherwisewillfail.

contentAsString(route(app,FakeRequest(GET,

"/rnd/rxbat")).get)mustBe"2.3000000000000007"

}

}

}

Wecanrunthesemixedtests,andtheywillallpass.

$activator"test-onlyApplicationSpec"

Youwillseethisresult:

OK,wearealmostdone.Wejustneedtoaddsometestsforthemicroservicecalledng-

microservice,whichwecreatedinChapter4,DevelopingReactiveBackingServices.

NGServiceImplTestSpec.scalaYourNGServiceImplTestSpec.scalafileshouldhavethefollowingcode:

classNGServiceImplTestSpecextendsPlaySpec{

"TheNGServiceImpl"must{

"GenerateaRamdonnumber"in{

valservice:NGContract=newNGServiceImpl

valdouble=service.generateDouble

assert(double>=1)

}

"Generatealistof3Ramdonnumbers"in{

valservice:NGContract=newNGServiceImpl

valdoubles=service.generateDoubleBatch(3)

doubles.sizemustBe3

assert(doubles(0)>=1)



}

}

}

Sohere,intheprecedingcode,wehavetwomethodstotestthetwooperationsthatwehaveinourmicroservice.Firstwegenerateonedouble,andthenweaskforalistofthreedoubles.Asyoucansee,wejustcheckifwegetapositivedoublebackfromtheservice,andthat'sit.Sincetheresultisnotpredictable,thisisagoodwaytotestit.Sometimes,evenwhentheresultispredictable,youwanttestslikethis.Why?Becauseitmakesthetestsmorereliable,andoften,whenweusetoomanyhardcorevalues.Thevaluescouldbechangingandbreakingourtests,andthat'snotcool.Let'srunitontheconsole.

$activator"test-onlyNGServiceImplTestSpec"

Hereistheresultthatweget:

Nowlet'smoveontothecontroller,anddosomecontrollertesting.

NGServiceEndpointControllerTest.scalaYourNGServiceEndpointControllerTest.scalafileshouldcontainthefollowingcode:

classNGServiceEndpointControllerTestextendsPlaySpecwith

OneServerPerSuitewith

OneBrowserPerSuitewithHtmlUnitFactory{

valinjector=newGuiceApplicationBuilder()

.injector

valws:WSClient=injector.instanceOf(classOf[WSClient])



"NGServiceEndpointController"must{

"returnasingledouble"in{

valfuture=ws.url(s"http://localhost:${port}/double")



responsemustnotbeempty

assert(newjava.lang.Double(response)>=1)

}

"returnalistof3doubles"in{

valfuture=ws.url(s"http://localhost:${port}/doubles/3")



responsemust(notbeemptyandinclude("[")and

include("]"))

}

}

}

HerewehavetoinjecttheWSClientlibrarysowecancallthecontroller.Thiscontrollerhastwomethodsliketheservicewetestedbefore.ThesecondmethodreturnsaJSONstructure.Thenwecheckfor"["and"]"tomakesurethatthearrayispresent,sincethisisalistofthreenumbers.

Weusetheassertfunctiontochecktheresponsefromthecontroller,andtobe100%surethateverythingisokay.Let'srunit.

$activator"test-onlyNGServiceEndpointControllerTest"

Refertothefollowingscreenshottoseethetestresult:

Great!Wehavecoveredprettymucheverything.

Inthischapter,weranallkindsoftests.Wealwaysusedthecommand$activator"test-onlyxxx";thereasonforthisistosavetime.However,itisverycommontorunalltests.Youcandothatinbothprojects;wehavetojusttype$activatortest.

Whenrunningallthetestsintheng-microserviceproject,wegettheresultshowninthefollowingscreenshot:

Ontheotherhand,runningallthetestsintheReactiveWebStoreprojectgivestheresultshowninthenextscreenshot:

SummaryInthischapter,youlearnedhowtodotests.WeaddedseveraltestsforyourScalaandPlayframeworkprojects.Youalsolearnedaboutunittestingprinciples,testingScalaapplicationswithJUnit,BDDprinciples,testingwithScalaTest,testingPlayframeworkapplicationswithScalaTest,andrunningtestsinActivator/SBT.

Inthenextchapter,youwilllearnmoreaboutpersistenceusingSlick,whichisreactive.Wewillalsochangeourtestsalittlebitinordertoworkwithadatabase.

Chapter6.PersistencewithSlickInthepreviouschapters,youlearnedtobootstrapyourapplicationusingActivator,wedevelopedourwebapplicationusingScalaandPlayframework,andweaddedReactivemicroservicescallsusingRxScalafordataflowcomputations.WeperformedunittestsandcontrollertestingusingtheBDDandPlayframeworks.

Inthischapter,youwilllearnhowtoachieverelationaldatabasepersistence.Sofar,wehaveourapplicationupandrunning.However,weareusingin-memorypersistencewithHashMap.Nowwewillupgradeourapplicationtouseproperpersistence.Inordertoachievethis,wewilluseareactivedatabasepersistenceframeworkcalledSlick.


PrinciplesofdatabasepersistencewithSlickWorkingwithFunctionalRelationalMappinginourapplicationCreatingQuerieswithSQLsupportImprovingcodewithAsyncdatabaseoperations

Wewilldosomerefactoringinourapplication.Step-by-step,wewillcreateallthetablesandpersistenceclassesthatweneedtohaveSlickworkingwithourPlayframeworkapplication.Testswillberefactoredaswellinordertotesttheapplicationlogic,andskipthedatabasepersistencepart.

IntroducingtheSlickframeworkScalaLanguageIntegratedConnectionKit(Slick)isaScalamodernframework,whichallowsworkingwithdatausingabstractionsthatareverysimilartoScalacollections.YoucanwritedatabasequeriesinbothSQLandScalacode.WritingScalacodeinsteadofSQLisbetter,becauseweleveragethecompiler,andhence,thisapproachislesserror-prone.Also,itbecomeseasiertomaintainthecode,sincethecompilerwillhelpyoubypointingoutwherethecodebreaks,ifithappens.

SlickisaFunctionalRelationalMapping(FRM)library.ThoseofyouwhocomefromaJavabackground,andarefamiliarwithObjectRelationalMapping(ORM)frameworkssuchasHibernate,willseethatSlickhassimilarconcepts.Basically,youcreateaScalaclass,whichwillexplicitlymaptoarelationaltable.SlickFRMideasareinspiredbyMicrosoft'sLINQframework.

Slickisreactivebydesign,andworksinanasynchronousnon-blockingIOmodel.UsingSlickyouhavethefollowingadvantages:

Resilience:AcommonissueisthataheavyloadontheDBandapplicationcreatesmorethreads,andmakesthesituationworse.Slickcanfixthisproblem,becauseitqueuesdatabaseoperationsintheDB.EfficientResourcesutilization:Slickcanbetunedforparallelismintermsofthenumberofactivejobsandsuspendeddatabasesessions.SlickalsohasacleandemarcationbetweenI/OandCPU-intensivecode.

MySQLsetupWewilluseSlickwithMySQL5.6.However,SlicksupportsotherrelationaldatabaseslikeOracle,SQLServer,DB2,andPostgres.Firstofall,weneedtoinstallMySQLinourmachine.Opentheconsole,andperformthefollowingsteps(forUbuntuLinux,otherOS(Windows/Mac),anddistros,checkouthttp://dev.mysql.com/downloads/mysql/):

$sudoapt-getinstallmysql-server-y

$mysql--version

$servicemysqlstatus

Afterinstallationwithapt-get,whenyouruntheothertwocommands,youshouldseeanoutputlikethis:

MySQLInstallation

OncetheinstallationisdoneandtheMySQLserverisupandrunning,wecanmoveonandcreatethedatabase.Inordertogetthis,wewillneedtoopentheMySQLconsole.Fordevelopmentreasons,Ididnotputapasswordforroot.However,forproduction,itisstronglyrecommendedthatyoudouseastrongpassword.

Executethefollowingcommand:

$mysql-uroot-p

Thiswillgiveoutputasfollows:

http://dev.mysql.com/downloads/mysql/

MySQLConsole

OnceyouentertheMySQLconsole,youcancreatethedatabase.WewillcreateadatabasenamedRWS_DBusingthefollowingcommand:

$CREATEDATABASERWS_DB;


Youcantype$SHOWDATABASES;inordertogetalistofalltheavailabledatabasesinMySQL.Allset,wehaveourdatabaseupandrunning.

ConfiguringSlickinourPlayframeworkappFirst,weneedtoadddependenciestothebuild.sbtfile.WewillneedtoremoveorcommentalibrarycalledJDBCandaddtheplay-slicklibrariesandMySQLjavadriver.

Thisisdoneasfollows:

name:="""ReactiveWebStore"""

version:="1.0-SNAPSHOT"

lazyvalroot=(projectinfile(".")).enablePlugins(PlayScala)


libraryDependencies++=Seq(//jdbc,

cache,

ws,

"org.scalatestplus.play"%%"scalatestplus-play"%"1.5.1"%

Test,

"com.netflix.rxjava"%"rxjava-scala"%"0.20.7",

"com.typesafe.play"%%"play-slick"%"2.0.0",

"com.typesafe.play"%%"play-slick-evolutions"%"2.0.0",

"mysql"%"mysql-connector-java"%"6.0.3"

)

resolvers+="scalaz-bintray"at"http://dl.bintray.com/scalaz/releases"


Asyoucanseeintheprecedingcode,wecommentouttheJDBClibrary,andaddthreenewdependencies:

"com.typesafe.play"%%"play-slick"%"2.0.0",

"com.typesafe.play"%%"play-slick-evolutions"%"2.0.0",

"mysql"%"mysql-connector-java"%"6.0.3"

Youcangototheconsoleandrunthecommands$activator,$reload,and$compileinordertogetSBTtodownloadallthenewdependencies.

ConfigurethedatabaseconnectionSlickneedstobeconfiguredtoaccesstheMySQLdatabasethatwecreated.UnderthefolderReactiveWebStore/conf,weneedtoedittheapplication.conffileandaddthedatabaseconnectionURLandsettingsasfollows:

#Defaultdatabaseconfiguration

slick.dbs.default.driver="slick.driver.MySQLDriver$"

slick.dbs.default.db.driver="com.mysql.cj.jdbc.Driver"

slick.dbs.default.db.url="jdbc:mysql://127.0.0.1:3306/RWS_DB?

useUnicode=true&useJDBCCompliantTimezoneShift=

true&useLegacyDatetimeCode=false&serverTimezone=UTC"

slick.dbs.default.db.user="root"

slick.dbs.default.db.password=""

FPMMappingThenextstepistocreateFPMmappingbetweenourScalacodeandMySQLtablesunderReactiveWebStore/app,wewillcreateanewpackagecalleddao.DAOstandsforDatabaseAccessObject(DAO),andisawell-knownOOpattern.SowewillcreatesomeDAOclasseshere.Firstwewilldefineabasetrait,whichwilldefinethebehaviorandcodecapabilityforeachofourdaopackages.

WewillstartwithBaseDao.scala:

packagedao

importslick.lifted.TableQuery

importscala.concurrent.Future

/**

*Definesbasedaostructureeverydaoshouldhave.

*/

traitBaseDao[T]{

deftoTable():TableQuery[_]

deffindAll():Future[Seq[T]]

defremove(id:Long):Future[Int]

definsert(o:T):Future[Unit]

defupdate(o:T):Future[Unit]

deffindById(id:Long):Future[Option[T]]

}

Wewillhavethreedaopackages:ProductDao,ImageDao,andReviewDao.Eachdaowillbeabletoperformanoperation,butoveradifferentMySQLtable.Accordingtothetraitwejustdefined,wewillbeabletodothefollowing:

findAll:Findalldataforaspecifictableremove:DeleteaniteminatablebyIDinsert:Addnewdatatoatableupdate:UpdatedatainatablefindbyId:Getaspecificrecordinatable,filteredbyIDtoTable:ReturnthetableFRMmappingforthatdao.

ProductDaoWewillstartwithhavingalookatProductDao.scala:

packagedao

traitIProductDaoextendsBaseDao[Product]{

deffindAll():Future[Seq[Product]]

deffindById(id:Long):Future[Option[Product]]


definsert(p:Product):Future[Unit]

defupdate(p2:Product):Future[Unit]

}

classProductDao@Inject()(protectedvaldbConfigProvider:

DatabaseConfigProvider)

extends

HasDatabaseConfigProvider[JdbcProfile]withIProductDao{

importdriver.api._

classProductTable(tag:Tag)extendsTable[Product](tag,

models.ProductDef.toTable){

defid=column[Option[Long]]("ID",O.PrimaryKey)

defname=column[String]("NAME")

defdetails=column[String]("DETAILS")

defprice=column[BigDecimal]("PRICE")

def*=(id,name,details,price)<>(Product.tupled,

Product.unapply_)

}

overridedeftoTable=TableQuery[ProductTable]

privatevalProducts=toTable()

overridedeffindAll():Future[Seq[Product]]=

db.run(Products.result)

overridedeffindById(id:Long):Future[Option[Product]]=

db.run(Products.filter(_.id===id).result.headOption)

overridedefremove(id:Long):Future[Int]=

db.run(Products.filter(_.id===id).delete)

overridedefinsert(p:Product):Future[Unit]=db.run(Products

+=p).map{_=>()}

overridedefupdate(p2:Product)=Future[Unit]{

db.run(

Products.filter(_.id===p2.id)

.map(p=>(p.name,p.details,p.price))

.update((p2.name,p2.details,p2.price))

)

}

}

ThisisthedaoimplementationforProduct.Wehavelotsofnewconceptshere,solet'stakealookateachstep,oneatatime.Asyoucansee,atraitcalledIProductDaowhichextendsfromBaseDaousinggenericstospecifythemodelProduct.

ThistraitisimportantfordependencyinjectionusingGuice.Wewillhavetwodaoimplementationsforeachmodel:oneimplementationusingSlickandMySQL,andtheotherusingourpreviousinMemorydatabasefortestingpurpose.

ThereisaclasstherecalledProductDaowhichisthedaoimplementationusingSlick.WeneedGuicetoinjectaclasshere,calledDatabaseConfigProvider,whichwillbeusedtoperformthedatabaseoperations.ProductDaoalsoneedstoextendHasDatabaseConfigProvider[JdbcProfile]toworkwiththedatabase.

Wealsoneedtoimportthedriverapiviathefollowingcommand:

Importdriver.api._

ThenextstepistocreateFRMmappingwithaclasscalledProductTable,whichextendstablepassingthemodel,whichinourcaseisaproduct.YoualsoneedtoannouncethenameoftheMySQLtable.Inordertogetthetablename,weuseacompanionobject,whichweneedtocreatearoundourmodels.WedoitthiswayinordertoavoidduplicatingtheMySQLtablenameeverywhere.

IntheProductTabletable,youcanseesomefunctionssuchasid,name,price,anddetails.Thesearetheexactnameofthefieldsofmodel.Product.However,wehavetoaddthemappingtotheMySQLtableontherightside.WedoitusingafunctioncalledcolumnwherewepassthetypeandtheexactMySQLfieldname.

Finally,weneedtorunaspecialprojectionfunctioncalled*topassallthefieldsonthemodel,whicharebeingmappedtotherelationaldatabase.

Nowwecanmovetothedaooperations.Asyoucansee,allthefunctionsusedb.runtoperformdataaccess.Thisisgreatbecause,asyoucanrealize,theyreturnaFuturesothedaowon'tbeblocking,andyoucandosomethingelse,forinstance,moredatabaseoperations,pre-optimizations,andvalidations.

OncewehaveaProductTabletable,wecancreateaSlickTableQuerywithittoperformdatabaseoperationsasiftheyareScalafunctions.Inordertolistalltheavailableproducts,wejustusethiscommand:

db.run(Products.result)

Itisassimpleasthat.ThiscodewillreturnaFuture[Seq[Products]].WecanalsofilterbyIDusingthis:

db.run(Products.filter(_.id===id).result.headOption)

So,first_.idistheidonthedatabase,andidistheonethatcomesbyparameter.Aftergettingtheresult,youcanseethatwecalledanotherfunctioncalledheadOption,whichmakessurethatwegettheresultasanoption.Thisisagreatpatterntorelyon,sincethedatamightnotbethereonthetable,andweavoidgettingNoSuchElementException.

Removingaproductisfairlytrivialaswell.Wejustusethefollowing:

db.run(Products.filter(_.id===id).delete)

ThisprecedingcodereturnsFuture[Int],countingthenumberofitemsthatweredeleted.IftherecordIDisnotfoundinthedatabase,theresultwillbe0.Weexpectittobealways1,sincewearegoingtodeletebyID.However,theAPIisgeneric,andif,let'ssay,youdeletebynameoranotherfield,youmighthavemultipledeletes.That'swhyitisanIntandnotaBoolean.

Insertingdataiseasytoo;wejustgivethefollowingcommand:

db.run(Products+=p).map{_=>()}

Asyoucansee,itisaverysimplemapfunctionasifwewereaddinganelementtoalist.Thiscodereturnsunit,whichmeansnothing.However,westillhaveaFuture,sothiscodeisnotblocking.

Toperformanupdate,thereisalittlebitmorecode,butitisstillsimpleattheendoftheday.

db.run(

Products.filter(_.id===p2.id)

.map(p=>(p.name,p.details,p.price))

.update((p2.name,p2.details,p2.price))

)

Firstweneedtoapplyafiltertoselecttherecordsthatwewillupdate.WepasstheID,becausewejustwanttoupdateasinglerecord.Thenweneedtoapplyamapfunctiontopickthefieldsthatwewanttoupdate;finally,weperformtheupdate,passingthenewvaluestotheupdatefunction.

Let'stakealookatthecompanionobjectfortheproductmodel.

HereisthecodeforModels.Product.scala:

objectProductDef{

deftoTable:String="Product"

}

Asyoucansee,thisisasimplehelpercompanionobjecttoholdtheMySQLtablename.

ReviewDAOWearedonewithProductDao,andnowweneedtomovetothereviewmodelandcreatedaoforreviews.Wewillperformstepssimilartotheoneswedidfortheproduct.

ReviewDao.scalaisasfollows:

packagedao

traitIReviewDaoextendsBaseDao[Review]{

deffindAll():Future[Seq[Review]]

deffindById(id:Long):Future[Option[Review]]


definsert(p:Review):Future[Unit]

defupdate(p2:Review):Future[Unit]

}

classReviewDao@Inject()(protectedvaldbConfigProvider:


extendsHasDatabaseConfigProvider[JdbcProfile]withIReviewDao{

importdriver.api._

classReviewTable(tag:Tag)extendsTable[Review](tag,

models.ReviewDef.toTable){


defproductId=column[Option[Long]]("PRODUCT_ID")

defauthor=column[String]("AUTHOR")

defcomment=column[String]("COMMENT")

def*=(id,productId,author,comment)<>(Review.tupled,

Review.unapply_)

}

overridedeftoTable=TableQuery[ReviewTable]

privatevalReviews=toTable()

overridedeffindAll():Future[Seq[Review]]=

db.run(Reviews.result)

overridedeffindById(id:Long):Future[Option[Review]]=

db.run(Reviews.filter(_.id===id).result.headOption)


db.run(Reviews.filter(_.id===id).delete)

overridedefinsert(r:Review):Future[Unit]=

db.run(Reviews+=r).map{_=>()}

overridedefupdate(r2:Review)=Future[Unit]{

db.run(

Reviews.filter(_.id===r2.id)

.map(i=>(i.productId,i.author,i.comment))

.update((r2.productId,r2.author,r2.comment))

)

}

}

Intheprecedingcode,wehavetheelementsthatwesawinProductDao.ThereisaninterfacefordaocalledIReviewDao,whichextendsBaseDaousingthereviewmodel.WehavetheReviewDaoimplementationwiththeReviewTableFRMmapping.Wealsohaveacompanionobjectforthereviewmodel.

Review.scalaisasfollows:

objectReviewDef{

deftoTable:String="Review"

}

ImageDaoNowweneedtomovetoourlastdao,ImageDao.LikeProductDaoandReviewDao,wewillgothroughthesameideasandconceptsasimplementationtoo.

WewillnowlookatImageDao.scala:

packagedao

traitIImageDaoextendsBaseDao[Image]{

deffindAll():Future[Seq[Image]]

deffindById(id:Long):Future[Option[Image]]


definsert(p:Image):Future[Unit]

defupdate(p2:Image):Future[Unit]

}

classImageDao@Inject()(protectedvaldbConfigProvider:


extends

HasDatabaseConfigProvider[JdbcProfile]

withIImageDao{

importdriver.api._

classImageTable(tag:Tag)extendsTable[Image](tag,

models.ImageDef.toTable){


defproductId=column[Option[Long]]("PRODUCT_ID")

defurl=column[String]("URL")

def*=(id,productId,url)<>(Image.tupled,Image.unapply

_)

}

overridedeftoTable=TableQuery[ImageTable]

privatevalImages=toTable()

overridedeffindAll():Future[Seq[Image]]=

db.run(Images.result)

overridedeffindById(id:Long):Future[Option[Image]]=

db.run(Images.filter(_.id===id).result.headOption)


db.run(Images.filter(_.id===id).delete)

overridedefinsert(i:Image):Future[Unit]=

db.run(Images+=i).map{_=>()}

overridedefupdate(i2:Image)=Future[Unit]

{db.run(

Images.filter(_.id===i2.id)

.map(i=>(i.productId,i.url))

.update((i2.productId,i2.url))

)}

}

Wealsoneedtohaveacompanionobjecthelperfortheimage.

Image.scalaisasfollows:

objectImageDef{

deftoTable:String="Image"

}

SlickevolutionsSlickwon'tcreatethetableforus,unlesswecreateanevolution.SlickkeepstrackofthedatabasestateandcreatesandappliesSQLcommandsforus.EvolutionsneedbelocatedatReactiveWebStore/conf/evolutions/default,wheredefaultisthenameofthedatabaseweconfiguredinapplication.conf.EvolutionsneedtobenamedinasequentialwaysothatwecanpreserveorderandSlickcankeeptrackofthechanges.Rightnow,wewillcreateanevolutionforProductDao,becauseweneedaproducttable.

Thecodewillbeasfollowswiththename1.sql:

#---!Ups

CREATETABLEProduct(IDINTNOTNULLAUTO_INCREMENT,NAMEVARCHAR(100)NOT

NULL,DETAILSVARCHAR(250),PRICEDOUBLENOTNULL,PRIMARYKEY(ID));

#---!Downs

#droptable"Product";

Weneedevolutionsforthreviewandimageaswell.Soweneedtocreate2.sqlfortheimageand3.sqlforthereview.

Thecodewillbeasfollowsfor2.sql:

#---!Ups

CREATETABLEImage(IDINTNOTNULLAUTO_INCREMENT,PRODUCT_IDINTNOTNULL,URL

VARCHAR(250),PRIMARYKEY(ID));

#---!Downs

#droptable"Product";

Thecodewillbeasfollowswiththename3.sql:

#---!Ups

CREATETABLEReview(IDINTNOTNULLAUTO_INCREMENT,PRODUCT_IDINTNOT

NULL,AUTHORVARCHAR(250),COMMENTVARCHAR(250),PRIMARYKEY(ID));

#---!Downs

#droptable"Review";

RefactoringservicesWeneedtochangethedefaultbasetraitforourdaopackagestoreturnFuturesnow.

Let'sstartwithBaseServices.scala:

packageservices


traitBaseService[A]{

definsert(a:A):Future[Unit]

defupdate(id:Long,a:A):Future[Unit]


deffindById(id:Long):Future[Option[A]]

deffindAll():Future[Option[Seq[A]]]

}

Thislastimplementationreflectswhat'shappeninginthedaopackages.Nowwecanmovetotheservicesimplementation,andproceedwithourrefactoring.

NextweseeProductService.scala:

packageservices

traitIProductServiceextendsBaseService[Product]{

definsert(product:Product):Future[Unit]

defupdate(id:Long,product:Product):Future[Unit]


deffindById(id:Long):Future[Option[Product]]

deffindAll():Future[Option[Seq[Product]]]

deffindAllProducts():Seq[(String,String)]

}

@Singleton

classProductService

@Inject()(dao:IProductDao)

extendsIProductService{


defaultContext

definsert(product:Product):Future[Unit]={

dao.insert(product);

}

defupdate(id:Long,product:Product):Future[Unit]={

product.id=Option(id.toInt)

dao.update(product)

}

defremove(id:Long):Future[Int]={

dao.remove(id)

}

deffindById(id:Long):Future[Option[Product]]={

dao.findById(id)

}

deffindAll():Future[Option[Seq[Product]]]={

dao.findAll().map{x=>Option(x)}

}


valfuture=findById(id)

valentry=Awaits.get(5,future)



}

deffindAllProducts():Seq[(String,String)]={

valfuture=this.findAll()

valresult=Awaits.get(5,future)

valproducts:Seq[(String,String)]=result

.getOrElse(Seq(Product(Some(0),"","",0)))

.toSeq

.map{product=>(product.id.get.toString,product.name)}

returnproducts

}

}

Thereareacoupleofchangeshere.First,weinjectanIProductDao,andletGuicefigureouttherightinjectionthatweneedtobeabletotestwithouroldin-memoryHashMapimplementation,whichwillbecoveredlaterinthischapter.

Thechangesinvolvenewfunctionsignatures,usingAwaits,andusingSeqinsteadofList.

Let'smovetoonReviewService.scalanow.

packageservices

traitIReviewServiceextendsBaseService[Review]{

definsert(review:Review):Future[Unit]

defupdate(id:Long,review:Review):Future[Unit]


deffindById(id:Long):Future[Option[Review]]

deffindAll():Future[Option[Seq[Review]]]

}

@Singleton

classReviewService@Inject()(dao:IReviewDao)

extendsIReviewService{



definsert(review:Review):Future[Unit]={

dao.insert(review);}

defupdate(id:Long,review:Review):Future[Unit]={

review.id=Option(id.toInt)

dao.update(review)

}


dao.remove(id)

}

deffindById(id:Long):Future[Option[Review]]={

dao.findById(id)

}

deffindAll():Future[Option[Seq[Review]]]={


}





RuntimeException("CouldnotfindReview:"+id)

}

}

Intheprecedingcode,wehavethesamekindofchangesthatwemadefortheproduct.Let'smovetoImageService.scala,whichisourlastservice.

packageservices

traitIImageServiceextendsBaseService[Image]{

definsert(image:Image):Future[Unit]

defupdate(id:Long,image:Image):Future[Unit]


deffindById(id:Long):Future[Option[Image]]

deffindAll():Future[Option[Seq[Image]]]

}

@Singleton

classImageService@Inject()(dao:IImageDao)

extendsIImageService{



definsert(image:Image):Future[Unit]={

dao.insert(image)

}

defupdate(id:Long,image:Image):Future[Unit]={

image.id=Option(id.toInt)

dao.update(image)

}


dao.remove(id)

}

deffindById(id:Long):Future[Option[Image]]={

dao.findById(id)

}

deffindAll():Future[Option[Seq[Image]]]={


}





RuntimeException("CouldnotfindImage:"+id)

}

}

Wehaverefactoredallservicestousethenewdaopackagesimplementation.Nowthenextstepisthemovetothecontrollers.

RefactoringcontrollersNowwehaveallthedaopackagesimplementedwiththerespectivedatabaseevolutions.However,ourservicesexpectedadifferentcontract,sincewewereusinganin-memorydatabasebefore.Let'srefactortheproductcontroller:

packagecontrollers

@Singleton


service:IProductService)


valproductForm:Form[Product]=Form(

mapping(


"name"->nonEmptyText,

"details"->text,

"price"->bigDecimal

)(models.Product.apply)(models.Product.unapply)

)


valproducts=Awaits.get(5,service.findAll())

.getOrElse(Seq())

Logger.info("indexcalled.Products:"+products)

Ok(views.html.product_index(products))

}




}



valproduct=Awaits.get(5,service.findById(id)).get


productForm.fill(product)))

}




form=>{

BadRequest(views.html.product_details(None,form))

},

product=>{


Redirect(routes.ProductController.index).

flashing("success"->Messages("success.insert",

"newproductcreated"))

}

)

}




form=>{


form)).flashing("error"->"Fixtheerrors!")

},

product=>{

service.update(id,product)

Redirect(routes.ProductController.index).flashing

("success"->Messages("success.update",product.name))

}

)

}




valresult=Awaits.get(5,service.findById(id))

result.map{product=>

service.remove(id)

Redirect(routes.ProductController.index).flashing("success"

->Messages("success.delete",product.name))


}

}

Therearetwobigchangesintheprecedingcodedespitethenewfunctionsignatures.First,weuseautilityfunctioncalledgetfromaclasscalledAwaits.Thisisneededsothatwewaitfortheresulttocomebackfromthedatabase.Second,whenweflashtheresult,wenolongershowtheid,wejustdisplayatextmessage.Let'stakealookattheAwaitsimplementationinUtils.Awaits.scala,whichisasfollows:

packageutils

objectAwaits{

defget[T](sec:Int,f:Future[T]):T={

Await.result[T](f,secseconds)

}

}

AwaitsisjustasimpleutilityclassthatwaitsforaperiodoftimetogetaFutureresult.WeneedtoaddsometweaksinReviewControllerandImageControlleraswell.

WewillfirstexploreReviewController.scala:

packagecontrollers

@Singleton


(valmessagesApi:MessagesApi,valproductService:IProductService,



valreviewForm:Form[Review]=Form(

mapping(



"author"->nonEmptyText,

"comment"->nonEmptyText

)(models.Review.apply)(models.Review.unapply)

)


valreviews=Awaits.get(5,service.findAll()).getOrElse(Seq())

Logger.info("indexcalled.Reviews:"+reviews)

Ok(views.html.review_index(reviews))

}



Ok(views.html.review_details(None,

reviewForm,productService.findAllProducts))

}



valreview=Awaits.get(5,service.findById(id)).get


reviewForm.fill(review),productService.findAllProducts))

}




form=>{

BadRequest(views.html.review_details(None,

form,productService.findAllProducts))

},

review=>{

if(review.productId==null||review.productId.isEmpty){

Redirect(routes.ReviewController.blank).flashing("error"

->"ProductIDCannotbeNull!")

}else{

Logger.info("Review:"+review)


review.productId.getOrElse(0)==0)thrownew

IllegalArgumentException("ProductIdCannotBeNull")


Redirect(routes.ReviewController.index).


"newReview"))

}

}

)

}




form=>{


form,productService.findAllProducts)).

flashing("error"->"Fixtheerrors!")

},

review=>{

service.update(id,review)

Redirect(routes.ReviewController.index).


review.productId))

}

)

}





result.map{review=>

service.remove(id)


>Messages("success.delete",review.productId))


}

}

ForReviewController,wehavemadethesamechangesthatwedidfortheproduct,thatis,theuseofAwaitsandlabelsonflashreturns.

Let'smoveontothefinalcontroller:ImageController.scala.

packagecontrollers

@Singleton






valimageForm:Form[Image]=Form(

mapping(



"url"->text

)(models.Image.apply)(models.Image.unapply)

)


valimages=Awaits.get(5,service.findAll()).getOrElse(Seq())

Logger.info("indexcalled.Images:"+images)

Ok(views.html.image_index(images))

}



Ok(views.html.image_details(None,

imageForm,productService.findAllProducts))

}



valimage=Awaits.get(5,service.findById(id)).get

Ok(views.html.image_details(Some(id),

imageForm.fill(image),productService.findAllProducts))

}




form=>{

BadRequest(views.html.image_details(None,form,

productService.findAllProducts))

},

image=>{

if(image.productId==null||

image.productId.getOrElse(0)==0){

Redirect(routes.ImageController.blank).flashing

("error"->"ProductIDCannotbeNull!")

}else{

if(image.url==null||"".equals(image.url))

image.url="/assets/images/default_product.png"




"newimage"))

}

}

)

}




form=>{

Ok(views.html.image_details(Some(id),form,

null)).flashing("error"->"Fixtheerrors!")

},

image=>{

service.update(id,image)

Redirect(routes.ImageController.index).flashing

("success"->Messages("success.update",image.id))

}

)

}





result.map{image=>

service.remove(id)

Redirect(routes.ImageController.index).flashing("success"

->Messages("success.delete",image.id))


}

}

ConfiguringDAOpackagesinGuiceWeneedtoconfiguretheinjectionsforthethreenewdaopackagesthatwecreated.SowetoneedtoaddthreelinesinthefileModule.scala.PleaseopenthefileinyourIDE,andaddthefollowingcontent:

bind(classOf[IProductDao]).to(classOf[ProductDao]).asEagerSingleton()

bind(classOf[IImageDao]).to(classOf[ImageDao]).asEagerSingleton()

bind(classOf[IReviewDao]).to(classOf[ReviewDao]).asEagerSingleton

Thewholefile,Module.scala,shouldlooklikethis:

/**

*ThisclassisaGuicemodulethattellsGuicehowtobindseveral

*differenttypes.ThisGuicemoduleiscreatedwhenthePlay

*applicationstarts.

*Playwillautomaticallyuseanyclasscalled`Module`thatisin

*therootpackage.Youcancreatemodulesinotherlocationsby

*adding`play.modules.enabled`settingstothe`application.conf`

*configurationfile.

*/





//AskGuicetocreateaninstanceofApplicationTimerwhen

//theapplicationstarts.


bind(classOf[IProductService]).

to(classOf[ProductService]).asEagerSingleton()

bind(classOf[IReviewService]).

to(classOf[ReviewService]).asEagerSingleton()

bind(classOf[IImageService]).

to(classOf[ImageService]).asEagerSingleton()

bind(classOf[IPriceSerice]).

to(classOf[PriceService]).asEagerSingleton()

bind(classOf[IRndService]).

to(classOf[RndService]).asEagerSingleton()

bind(classOf[IProductDao]).

to(classOf[ProductDao]).asEagerSingleton()

bind(classOf[IImageDao]).

to(classOf[ImageDao]).asEagerSingleton()

bind(classOf[IReviewDao]).

to(classOf[ReviewDao]).asEagerSingleton()

}

}

RefactoringtestsAsyoumightexpect,mosttestsarenolongerworking.Wewillneedtoperformsomerefactoringhereaswell.Wewillrefactorourformerdaotomakeitgeneric,anditwillbeusedinintegrationtests(end-to-endtests).

Sincewewillcreateagenericdaosysteminmemoryforend-to-endtestingpurposes,weneedtochangeourmodelsalittlebit.First,weneedtocreateabasetraitforallthemodels.Thisisneededsowecantreatourmodelsasequals.

Let'shavealookatmodels.BaseModel.scala:

packagemodels

traitBaseModel{

defgetId:Option[Long]

defsetId(id:Option[Long]):Unit

}

Wealsoneedtomakeallourmodelsimplementthisnewtrait.SowewillneedtochangetheScalacodefortheproduct,image,andreview.Thisisverytrivial:wejustaddagetterandasetterfortheidfield.Youcanalsousescala.bean.BeanPropertyinsteadofwritingonebyyourself.

Yourmodels.Product.scalafileshouldlooksomethinglikethis:

packagemodels

caseclassProduct


varname:String,

vardetails:String,

varprice:BigDecimal)

extendsBaseModel{



details:"+details+",price:"+price+"}"

}

overridedefgetId:Option[Long]=id

overridedefsetId(id:Option[Long]):Unit=this.id=id

}

objectProductDef{

deftoTable:String="Product"

}

Asyoucanseeintheprecedingcode,weextendtheBaseModelmethod,andimplementgetIdandsetId.Weneedtodothesameforthereviewandimagemodels.

Yourmodels.Review.scalafileshouldlooklikethis:

packagemodels

caseclassReview



varauthor:String,

varcomment:String)

extendsBaseModel{


"Review{id:"+id+",productId:"+

productId.getOrElse(0)+",author:"+author+",comment:"

+comment+"}"

}



}

objectReviewDef{

deftoTable:String="Review"

}

Nowwemoveontothelastmodel.WeneedtoimplementitinImage.scala.

Yourmodels.Image.scalafileshouldlooklikethis:

packagemodels

caseclassImage



varurl:String)

extendsBaseModel{


"Image{productId:"+productId.getOrElse(0)+",url:"+

url+"}"

}



}

objectImageDef{

deftoTable:String="Image"

}

GenericmocksNowwehaveallthatweneedtocreateagenericmockimplementationandmockallthedaopackages.UnderthelocationReactiveWebStore/test/,wewillcreateapackagecalledmocks,andcreateacall,GenericMockedDao.

YourGenericMockedDao.scalafileshouldlooklikethis:

packagemocks

importmodels.BaseModel

classGenericMockedDao[T<:BaseModel]{



importscala.concurrent._



varinMemoryDB=newHashMap[Long,T]

varidCounter=newAtomicLong(0)

deffindAll():Future[Seq[T]]={

Future{

if(inMemoryDB.isEmpty)Seq()

inMemoryDB.values.toSeq

}

}

deffindById(id:Long):Future[Option[T]]={

Future{

inMemoryDB.get(id)

}

}


Future{

validateId(id)


1

}

}

definsert(t:T):Future[Unit]={

Future{


t.setId(Some(id))

inMemoryDB.put(id,t)

Unit

}

}

defupdate(t:T):Future[Unit]={

Future{

validateId(t.getId.get)

inMemoryDB.put(t.getId.get,t)

Unit

}

}





}

}

SotheGenericMockedDaocallexpectstheGenericparameter,whichcouldbeanyclassextendingfromBaseModel.Thenweuseanin-memoryHashMapimplementationandacountertosimulatedatabaseoperations.WerunalltheoperationsinsideFutures,sowedon'tbreakthenewsignaturethecodeisexpecting.NowwecancreatethreeMockedDaosforeachmodelweneed:product,review,andimage.

Yourmocks.ProductMockedDao.scalafileshouldlooklikethis:

packagemocks

classProductMockedDaoextendsIProductDao{

valdao:GenericMockedDao[Product]=new

GenericMockedDao[Product]()

overridedeffindAll():Future[Seq[Product]]={

dao.findAll()

}

overridedeffindById(id:Long):Future[Option[Product]]={

dao.findById(id)

}

overridedefremove(id:Long):Future[Int]={

dao.remove(id)

}

overridedefinsert(p:Product):Future[Unit]={

dao.insert(p)

}

overridedefupdate(p2:Product):Future[Unit]={

dao.update(p2)

}

overridedeftoTable:TableQuery[_]={

null

}

}

Asyoucanseehere,weimplementtheIProdutDaotrait,andwedelegatealloperationstogenericMockedDao.Sinceeverythingisin-memory,wedon'tneedtoimplementthetoTablefunction.Weneedtodothesameforthereviewandimage.

Yourmocks.ReviewMockedDao.scalafileshouldlooklikethis:

packagemocks

classReviewMockedDaoextendsIReviewDao{

valdao:GenericMockedDao[Review]=new

GenericMockedDao[Review]()

overridedeffindAll():Future[Seq[Review]]={

dao.findAll()

}

overridedeffindById(id:Long):Future[Option[Review]]={

dao.findById(id)

}


dao.remove(id)

}

overridedefinsert(p:Review):Future[Unit]={

dao.insert(p)

}

overridedefupdate(p2:Review):Future[Unit]={

dao.update(p2)

}


null

}

}

Exactlylikeproduct,wedelegatealloperationstoGenericMockedDao.Nowlet'smovetothelastone,theimage,andthenwecanfixthetests.

Yourmocks.ImageMockedDao.scalafileshouldlooklikethis:

packagemocks

classImageMockedDaoextendsIImageDao{

valdao:GenericMockedDao[Image]=newGenericMockedDao[Image]()

overridedeffindAll():Future[Seq[Image]]={

dao.findAll()

}

overridedeffindById(id:Long):Future[Option[Image]]={

dao.findById(id)

}


dao.remove(id)

}

overridedefinsert(p:Image):Future[Unit]={

dao.insert(p)

}

overridedefupdate(p2:Image):Future[Unit]={

dao.update(p2)

}


null

}

}

Okay,wehaveallthemocksthatweneedfornow.Wecanmoveontofixthetestspecs.Weneedtofixservicestestsandcontrollertest.Servicestestswillusemocks.Controllerstests,however,willusetherealdatabaseimplementation.Weneedtouseotherutilityclassesforcontrollertests.Locatedinthetestsourcefolder,weneedtocreateapackagecalledutils.

Yourutils.DBCleaner.scalafileshouldlooklikethis:

packageutils

objectDBCleaner{

valpool=Executors.newCachedThreadPool()

implicitvalec=ExecutionContext.fromExecutorService(pool)

defcleanUp():Unit={

Class.forName("com.mysql.cj.jdbc.Driver")

valdb=Database.forURL

("jdbc:mysql://127.0.0.1:3306/RWS_DB?useUnicode=

true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=

false&serverTimezone=UTC",

"root","")

try{

Await.result(

db.run(

DBIO.seq(

sqlu"""DELETEFROMProduct;""",

sqlu"""DELETEFROMImage;""",

sqlu"""DELETEFROMReview;""",

sqlu"""ALTERTABLEProductAUTO_INCREMENT=1""",

sqlu"""ALTERTABLEImageAUTO_INCREMENT=1""",

sqlu"""ALTERTABLEReviewAUTO_INCREMENT=1"""

)

)

,20seconds)

}catch{


}

}

}

DBCleanerwillconnecttotherealdatabaseandperformdeletestatementstocleanupalltabledata.Afterdeletingalldatainthetables,wealsoresetthesequenceinthedatabase;otherwise,ourtestswillnothavethepredictabilityweneedtodoassertions.

Asyoucanseeindb.run,wecanuseDBIO.seq,whichallowsustoexecutemultipleinstructionsonthedatabase.HerewearenotusingScalacode.WeareusingpureSQLstatements,sinceweneedtouseveryspecificMySQLfunctionstoresetthesequences.

Ifyouneed,youcoulduseallthesefunctionsinyourapplication.Thisisusefulifyouneedtouseaspecificdatabasefunction,ifyouhaveaverycomplexquery,orsometimes,becausethereisaperformanceissue.

MostfixeswedonowcenteraroundusingAwaitstowaitfortheFutureresult,andalsousingournewmocks.Forthecontrollertest,weneedtocalltheDBCleanerfunctionaswell.

ServicetestsNowwewillcreatetestsforservicestotestthem.Solet'sgetstarted.

YourProductServiceTestSpec.scalafileshouldlooklikethis:

classProductServiceTestSpecextendsPlaySpec{

"ProductService"must{

valservice:IProductService=newProductService(new

ProductMockedDao)

"insertaproductproperly"in{

valproduct=newmodels.Product(Some(1),"Ball","Awesome

Basketball",19.75)


}

"updateaproduct"in{

valproduct=newmodels.Product(Some(1),"Blue

Ball","AwesomeBlueBasketball",19.99)

service.update(1,product)

}

"notupdatebecausedoesnotexit"in{



}

}

"findtheproduct1"in{

valproduct=Awaits.get(5,service.findById(1))

product.get.idmustBeSome(1)

product.get.namemustBe"BlueBall"

product.get.detailsmustBe"AwesomeBlueBasketball"

product.get.pricemustBe19.99

}

"findall"in{

valproducts=Awaits.get(5,service.findAll())

products.get.lengthmustBe1

products.get(0).idmustBeSome(1)

products.get(0).namemustBe"BlueBall"

products.get(0).detailsmustBe"AwesomeBlueBasketball"

products.get(0).pricemustBe19.99

}

"findallproducts"in{

valproducts=service.findAllProducts()

products.lengthmustBe1

products(0)._1mustBe"1"

products(0)._2mustBe"BlueBall"

}

"remove1product"in{

valproduct=Awaits.get(5,service.remove(1))

productmustBe1

valoldProduct=Awaits.get(5,service.findById(1))

oldProductmustBeNone

}



Awaits.get(5,service.remove(-1))

}

}

}

}

Asyoucanseeintheprecedingcode,mostfixescenteraroundthenewsignaturesandthefactweareusingFuturesandneedtousetheAwaitsutilityandmocks.Wetesttheservicewithoutthedatabasecallviathiscode:

valservice:IProductService=newProductService(newProductMockedDao)

Wecanmoveontothenextservice,whichwillbethereview.

YourReviewServiceTestSpec.scalafileshouldlooklikethis:

classReviewServiceTestSpecextendsPlaySpec{

"ReviewService"must{

valservice:IReviewService=newReviewService(new

ReviewMockedDao)

"insertareviewproperly"in{

valreview=newmodels.Review

(Some(1),Some(1),"diegopacheco","TestingisCool")


}

"updateareviewt"in{

valreview=newmodels.Review

(Some(1),Some(1),"diegopacheco","TestingsosoCool")

service.update(1,review)

}



Awaits.get(5,service.update(333,null))

}

}

"findthereview1"in{

valreview=Awaits.get(5,service.findById(1))

review.get.idmustBeSome(1)

review.get.authormustBe"diegopacheco"

review.get.commentmustBe"TestingsosoCool"

review.get.productIdmustBeSome(1)

}

"findall"in{

valreviews=Awaits.get(5,service.findAll())



reviews.get(0).authormustBe"diegopacheco"

reviews.get(0).commentmustBe"TestingsosoCool"


}

"remove1review"in{

valreview=Awaits.get(5,service.remove(1))

reviewmustBe1

valoldReview=Awaits.get(5,service.findById(1))

oldReviewmustBeNone

}




}

}

}

}

Thatwasthereviewspecservicetestcode.Weapplythesamechangesaswedidforproduct.Nowweneedtomoveontothelastservicetest,whichwillbetheimage.

YourImageServiceTestSpec.scalafileshouldlooklikethis:

classImageServiceTestSpecextendsPlaySpec{

"ImageService"must{

valservice:IImageService=newImageService(new

ImageMockedDao)

"insertaimageproperly"in{

valimage=newmodels.Image

(Some(1),Some(1),"http://www.google.com.br/myimage")


}

"updateaimage"in{

valimage=newmodels.Image

(Some(2),Some(1),"http://www.google.com.br/myimage")

service.update(1,image)

}



Awaits.get(5,service.update(333,null))

}

}

"findtheimage"in{

valimage=Awaits.get(5,service.findById(1))

image.get.idmustBeSome(1)

image.get.productIdmustBeSome(1)

image.get.urlmustBe"http://www.google.com.br/myimage"

}

"findall"in{

valreviews=Awaits.get(5,service.findAll())




reviews.get(0).urlmustBe"http://www.google.com.br/myimage"

}

"remove1image"in{

valimage=Awaits.get(5,service.remove(1))

imagemustBe1

valoldImage=Awaits.get(5,service.findById(1))

oldImagemustBeNone

}




}

}

}

}

Wehavefixedalltheservicestests.Nowweneedtofixthecontrollertests.

ControllertestsNowlet'sfixthecontrollertests.Thefirstonewillbetheproductcontroller.

YourProductControllerTestSpec.scalafileshouldlooklikethis:

classProductControllerTestSpec

extends

PlaySpec

withOneServerPerSuitewithOneBrowserPerSuitewithHtmlUnitFactory{


DBCleaner.cleanUp()

"insertanewproductshouldbeok"in{


clickonid("name")

enter("BlueBall")



clickonid("price")

enter("17.55")

submit()

}

"detailsfromtheproduct1shouldbeok"in{


textField("name").valuemustBe"BlueBall"


andsimpleproduct"


}

"updateproduct1shouldbeok"in{


textField("name").value="BlueBall2"

textField("details").value="BlueBallisaAwesomeand

simpleproduct2"

textField("price").value="17.66"

submit()


textField("name").valuemustBe"BlueBall2"


andsimpleproduct2"


}

"deleteaproductshouldbeok"in{


clickonid("name")

enter("BlueBall")



clickonid("price")

enter("17.55")

submit()

goTo(s"http://localhost:${port}/product")


}

"Cleanupdbintheend"in{

DBCleaner.cleanUp()

}

}

}

TheControllerproducttestneedstocalltheDBCleanerfunctionatthebeginningofthetesttomakesurethatthedatabaseisinawell-knownstate;additionally,andafterrunningallthetests,weneedtocleanupthedatabasejusttobesafe.

Wewillnowapplythesamechangesforthereviewandimagecontrollertests.

YourReviewControllerTestSpecfileshouldlooklikethis:

classReviewControllerTestSpec

extendsPlaySpec


DBCleaner.cleanUp()


"insertanewreviewshouldbeok"in{


clickonid("name")

enter("BlueBall")



clickonid("price")

enter("17.55")

submit()



clickonid("author")




submit()

}

"detailsfromthereview1shouldbeok"in{


textField("author").valuemustBe"diegopacheco"

textField("comment").valuemustBe"Testsareamazing!"

}

"updatereview1shouldbeok"in{


textField("author").value="diegopacheco2"

textField("comment").value="Testsareamazing2!"

submit()


textField("author").valuemustBe"diegopacheco2"

textField("comment").valuemustBe"Testsareamazing2!"

}

"deleteareviewshouldbeok"in{



clickonid("author")




submit()

goTo(s"http://localhost:${port}/review")

clickonid("btnDelete")}


DBCleaner.cleanUp()

}

}

}

Alright,wehavethetestsforthereviewcontrollerfixed.Nowwecanmovetothelastcontrollertestfortheimage.

YourImageControllerTestSpec.scalafileshouldlooklikethis:

classImageControllerTestSpec

extendsPlaySpec


DBCleaner.cleanUp()


"insertanewimageshouldbeok"in{


clickonid("name")

enter("BlueBall")



clickonid("price")

enter("17.55")

submit()



clickonid("url")

enter("https://thegoalisthering.files.wordpress.com/2012/01/

bluetennisball_display_image.jpg")

submit()

}

"detailsfromtheimage1shouldbeok"in{


textField("url").valuemustBe

"https://thegoalisthering.files.wordpress.com/2012/01/

bluetennisball_display_image.jpg"

}

"updateimage1shouldbeok"in{


textField("url").value=


bluetennisball_display_image2.jpg"

submit()


textField("url").valuemustBe


bluetennisball_display_image2.jpg"

}

"deleteaimageshouldbeok"in{



clickonid("url")

enter("https://thegoalisthering.files.wordpress.com/2012/01/

bluetennisball_display_image.jpg")

submit()

goTo(s"http://localhost:${port}/image")


}


DBCleaner.cleanUp()

}

}

}

Allright,allthecontrollertestsarefixednow.WecanrunalltheteststodoublecheckwhethereverythingisOK.

Runthefollowingcommand:

$activatortest

Yougetoutputasshowninthefollowingscreenshot:

Ifyouhaveproblemsrunningtheapplication(coveredinthenextsection),applytheevolution,andthenyoucanrunthetestsagain.Testsmighttakesometime,dependingonyourhardware.

RunningtheapplicationNowitistimetoruntheapplicationusing$activatorrun.Openyourwebbrowser,andgotohttp://localhost:9000/.Onceyoudothat,Playwilldetectthattheapplicationneedsevolutions,andwillapplythethreeevolutionswehave(1.sql,2.sql,and3.sql).However,youwillneedtoclickonthebuttontoapplytheevolution.

Afteryouclickontheredbutton,Applythisscriptnow!,Slickwillcreatethetables,andredirectyoutotheapplication.

SummaryWiththis,wereachtheendofthechapter.YoulearnedhowtoperformdatabasepersistenceusingSlick.YoualsolearnedhowtodoFRMmapping,andwerefactoredourapplicationandtestssotheyworkwithreactivepersistenceandthePlayframework.WethenexplainedhowtoaccessthedatabaseusingScalacode,andperformoperationsusingSQL.

Inthefollowingchapter,wewillseemoreaboutreports,andwewilluseourdatabasetogeneratereportsbasedonourPlayframeworkapplication.

Chapter7.CreatingReportsUpuntilnow,welearnedhowtobootstrapourapplicationusingActivator,developourwebapplicationusingtheScalaandPlayframework,andaaddreactivemicroservicescallusingRxScalafordataflowcomputations.WealsoperformedunittestandcontrollertestingusingtheBDDandPlayframework.Then,wepersisteddataintoMySQLusingSlick.Nowwewillmoveonwithourapplication.

Inthischapter,youwilllearnhowtowritereportswithJasperReports.JasperReportsisaverysolidreportingsolutionforJava,anditcanbeusedinScalaveryeasily.WewillcreatedatabasereportsusingJasper,andchangeourapplicationtohavesuchfunctionality.


UnderstandingJasperReportsAddingdatabasereportstoourapplication

IntroducingJasperReportsJasperReports(http://community.jaspersoft.com/project/jasperreports-library)isaverypopularandsolidreportssolutionthatcangeneratereportsinseveralformats,suchas:

HTMLExcelWordOpenOfficeformatPDF

Inordertogetyourreports,youhaveavisualtoolcalledJaspersoftStudio,inwhichyoucandraganddropelementssuchaslabels,images,datafields,andmuchmore.Jasperwillstorethismetadata(thereportdefinition)inanXMLfile,alsoknownasJRXML.Ifyouwant,youcaneditandworkwiththisXMLwithoutanyeditor;however,itiswaybettertousetheJaspersoftStudiotooltogainproductivity.

Jaspercanworkwithseveraldatasources,suchasdatabases,XML,orevenobjectsinmemory.Forthisbook,wewillusethedatabasedatasourcetoaccessourMySQLdatabase.

http://community.jaspersoft.com/project/jasperreports-library

JasperReportsworkflowJasperReportshasthesameexecutionstages,includingcompilingyourreportsandrenderinginaspecificformat,forexample,HTML.Thefirststageisthereportdesign.IfyouarenotusingtheJaspersoftStudiovisualtool,weassumethatyouhaveyourJRXMLfile.ThenextstepistocompileJRXMLintoaJasperfile.Thiscompilationphasedoesn'tneedtohappeneverytime;it'sneededonlyifyouchangetheJRXML.Otherwise,youcanusethesameJasperfile.TherearesomestrategiestocachetheJasperfile,sobasicallyyoucandoitonthebuildtimeoryoucancacheondemandintheapplication.Forourapplication,wewillbeusingthesecondapproach--cachingondemandintheapplication.

Thenextphaseistorenderorexport.YoucanexportthereporttothemanyformatsJaspersupports,suchasHTML,EXCEL,orPDF,forinstance.It'spossibletousethesamereportlayoutandexporttoasmanyformatsasyoulike.Forourapplication,wewillbeusingthePDFformat.

JaspersessionsAJRXMLhassectionsthatareevaluatedindifferentwaysandatdifferenttimes.Thefollowingdiagramshowsalltheavailablesessions:

Thedifferentsectionsareasfollows:

Title:ThisisprintedjustonetimePageHeader:ThisisprintedatthebeginningofallprintedpagesColumnHeader:ThisisprintedatthebeginningofeachdetailcolumnDetail:ThisiswhereeveryrecordreadfromthedatasourceisprintedColumnFooter:ThisisprintedattheendofeachdetailcolumnPageFooter:ThisisprintedattheendofallprintedpagesSummary:Thisisprintedattheendofthereport,andisoftenusedtoshowcalculations,totals,andsummarizationsingeneral

JasperisaveryflexiblereportsolutionthatalsoallowsustorungroovyscriptsinsideaJasperreporttododynamiccalculationsaswellasdynamiclayouts.Thisisusefulifyoudonotwanttoprintapagegivensomecondition,orbasedonwhatyouhaveinthedatabase,or

youdonotwanttoshowsomedata.

Next,wewillinstallJaspersoftStudioandstartcreatingreportsforourapplication.

InstallingJaspersoftStudio6Forthis,youwillneedtohaveJava8installed.Ifyoudon'thaveit,gobacktoChapter1,IntroductiontoFP,Reactive,andScala,andfollowthesetupinstructions.Jasperisreallygreatbecauseitworksonmultipleplatforms;however,itworksbetteronWindows.WeareusingLinux,sowewillneedtodealwithfonts.JasperReportsuseslotsofMicrosoft'scorefonts,suchasArialandTimesNewRoman.TherearesomeoptionstohavethesourcesonLinux.YoucanlookforamscorefontsinstalleronLinuxorjustcopythefontsfromWindows.

IfyouhaveadualbootLinux/Windowsinstallation,youcangotoyourWindowsdriveatthelocationWindowsDrive/Windows/Fonts.Youwillneedtocopyallfontfilesto/usr/share/fontsonLinuxandrun$sudofc-cache-fv.Thismighttakesometime--formyWindowsinstallation,itwasabout~300MBoffonts.YoucantestwhetheryouhaveWindowscorefontsonLinux.Openthewriterandcheckforthefonts.Youshouldseesomethingsimilartothis:

Whyisthissoimportant?BecauseJasperwon'tworkifyoudon'thavetherightfontinplace.Itwilljustthrowyourandomexceptionsthatwillnotmakesense,butitisverylikelytoberelatedtomissingfonts.

Oncewehavethefonts,wecangoaheadanddownloadJaspersoftStudio6.Forthisbook,wewillbeusingthe6.2.2version.Youcandownloaditfromhttp://community.jaspersoft.com/project/jasperreports-library/releases.IfyouareonLinux,it'shighlyrecommendedtousetheDEBpackage;otherwise,youwillneedtoinstallseveralotherdependencies.

OnceyoudownloadandinstallJaspersoftStudioandopentheprogram,youwillseeaUIsimilartothisonehere:

WehavesuccessfullyinstalledJaspersoftStudio.Now,wewillneedtoconfigureourMySQLdatasourceinordertostartcreatingreportsforourapplication.

http://community.jaspersoft.com/project/jasperreports-library/releases

ConfiguringMySQLDataAdapterinJaspersoftStudioOpenJaspersoftStudio6andclickonFile|New|DataAdapterWizard.Youwillseethefollowingscreen:

FilenameshouldbeMYSQL_DATAADAPTER.xml,andthenyoucanclickNext>.

Next,wewillneedtochoosethetypeofdatabaseadapter.Thereareseveraloptions,suchasCassandra,MongoDB,HBase,JSONfile,andsoon.

WeneedtopickDatabaseJDBCConnectionandclickNext>.

Now,wewillneedtoconfiguretheconnectiondetails.

Thefieldsshouldbecompletedasfollows:

Name:MySQLJDBCDriver:com.mysql.jdbc.DriverJDBCUrl:jdbc:mysql://localhost/RWS_DB?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC

Username:rootPassword:Thisneedsbeblank,orputthepasswordifyouareusingone.

WewillalsoneedtoconfigurethedriverintotheJaspersoftStudioclasspath.Aswearerunningtheapplicationinthesamebox,wealreadyhavetheMySQLdriverdownloadwithSBTonthe~/.ivy2/cache/mysql/mysql-connector-java/jars/mysql-connector-java-6.0.3.jarfolder.Wewilljustneedtopointitoutonthethirdtab,calledDriverClasspath.

Nowwecantesttheconnectiontoseeifit'sallgood.

Great!NowwehaveourMySQLDatabaseAdapterconfigured,andwearereadytostartcreatingreportsforyourapplication.

CreatingaproductreportTocreateaproductreport,clickonFile|New|JasperReport.ThenselecttheInvoicetemplate.

NowyoucanclickonNext>andwewillsetupthenameofthereport.ThefilenamewillbeProducts.jrxml.ClickonNext>.Then,wewillneedtoselecttheDataSource:MySQL.

Now,youwillneedtoruntheSelectname,details,pricefromProduct;query.

AftersettingtheSQLquery,youcanclickonNext>.

Next,youwillneedtopickthefieldsthatwillbeusedinthereport.Selectallthefieldsfromtheleftlistandmovethemtotherightlist.ThenclickonNext>.Wedon'tneedgrouporderingforthisreport,sojustskipthegroupandclickonNext>again.

Congratulations!Wefinishedthesetup.Wecantakealook(haveareportpreview)ofthereportusingJaspersoftStudio.JustclickonthenewreportcalledProducts.jxml.Wewillremoveallthefieldsthatwedon'tneed,aswellasthelogo.Thenthereportwilllooklikethis:

WewillchangethetitletoProductsanddropallotherinformationbuttheNAME,DETAILS,andPRICEheaders,whichwillberetained.Wewillalsokeepthe$F{NAME},$F{DETAILS},and$F{PRICE}fields,whichwillcomefromtheMySQLdatabase.

Now,wecanseethereportpreview.WewillneedtoclickonthebottomtabnamedPreview.Thereareseveralpreviewoptions.WewillhavetopickMySQLasadatasourcefromthetopofthescreenandtheexportedformat;here,weareusingJavatoseetheUI.Youcanalsopickotherformats,suchasPDF,forinstance.

Next,wewillneedtocreatereportsforreviewsandimages.

CreatingareviewreportNow,wewillcreatethereviewreport.Wewilluseaverysimilarprocesstotheonethatweusedfortheproductreport.Let'sgetstartedoncreatingareviewreport:

1. ClickonFile|New|JasperReport.SelecttheInvoicetemplateandclickonNext>.2. ThefilenamewillbeReviews.jrxml.ThenclickonNext>.3. ChooseMySQLfromDataAdapterandclickonNext>.4. Query(Text)shouldcontainthefollowingcodesnippet:

Selectp.name,r.author,r.comment

fromProductp,Reviewr

wherep.id=r.product_id;

5. ThenclickNext>.6. Selectallthefields:name,author,andcommentthenclickNext.>7. Let'sskipthegroupbysectionandclickonNextandthenFinish.8. Wewillremovealltemplatelabelsandfieldsandjustkeepthedatabasefields,sowe

shouldhavesomethinglikethis:

That'sit!Wehavethereviewreport.Ifyoulike,youcanclickonthePreviewtabatthebottomofthescreenandselectMySQLandJavatoseethereport.Keepinmindthatyouwillneedtohavedata;otherwise,itwillbeempty.

CreatinganimagereportNowwewillcreatetheimagereport.Wewillfollowaverysimilarprocesstotheoneweusedfortheproductandreviewreport.AswehaveanimageURL,wewillalsodisplaytheimage,sowewillneedtouseadifferentcomponent.Let'sgetstartedoncreatinganimagereport:

1. ClickonFile|New|JasperReport.2. SelecttheInvoicetemplateandclickonNext.3. ThefilenamewillbeImages.jrxml.ThenclickonNext.4. ChooseMySQLfromDataAdapterandclickonNext>.5. Query(Text)shouldcontainthefollowingcodesnippet:

Selectp.name,i.url

fromImagei,Productp

wherep.id=i.product_id;

6. ThenclickNext>.7. Selectallthefields:name,url,andthenclickNext>.8. Let'sskipthegroupbysectionandclickonNext>andthenFinish.

Nowwewillneedtoremovealllabelsandfields,aswedidfortheotherreports,andjustkeepthelabelsandfieldsfromthedataadapter.

WeneedtoaddanimagecomponentcalledImage.Youcanfinditinthepaletteattheright-handsidecalledBasicElements.Justdraganddropitintothedetailband,asshowninthefollowingscreenshot:

Selectacustomexpressionandthentype$F{url}.

That'sit!Nowthatwehavetheimagereportwithimages,it'stimetochangethePlayframeworkapplicationinordertorenderthisreportinPDFformatoverthere.

IntegratingJasperReportswithPlayframeworkWewillneedtocreateanewfolderunderReactiveWebStore/appcalledreports.Then,wewillcopyallthreenew.jrxmlfilesfromtheJaspersoftStudiotothisfolderandsetupthebuilddependencies.

build.sbtFirstofall,wewillneedtoaddnewdependenciestothebuild.sbtfile.

Yourbuild.sbtfileshouldlooklikethisafteraddingtheJasperdependencies:


//....Otherdependencies....

"net.sf.jasperreports"%"jasperreports"%"6.2.2"withSources()

,"net.sf.jasperreports"%"jasperreports-functions"%"6.2.2",

"net.sf.jasperreports"%"jasperreports-chart-themes"%"6.2.2"

)

resolvers+="Jasper"at

"https://jaspersoft.artifactoryonline.com/jaspersoft/repo/"

resolvers+="JasperSoft"at

"https://jaspersoft.artifactoryonline.com/jaspersoft/jaspersoft-

repo/"

resolvers+="Jasper3rd"at

"https://jaspersoft.artifactoryonline.com/jaspersoft/

jaspersoft-3rd-party/"

resolvers+="mondrian-repo-cache"at

"https://jaspersoft.artifactoryonline.com/jaspersoft/

mondrian-repo-cache/"

resolvers+="spring-mil"at"http://repo.spring.io/libs-milestone"

resolvers+="spring-rel"at"http://repo.spring.io/libs-release"

resolvers+="oss"at

"https://oss.sonatype.org/content/groups/public/"

So,basically,weaddedallJasperReportsdependenciesandresolvers,whichareabunchofremoterepositorieswhereSBTcanlookforthejarfiles.Youcanrunthe$activatorcompilecommandontheconsoleinordertoreloadthenewdependencies.Afterrunningcompile,itisimportanttogenerateeclipsefilesagain,soyouwillneedtorun$activatoreclipse.

GenericreportbuilderNowisthetimetocodeinScala.WewillcreateagenericreportbuilderinScala.UnderReactiveWebStore/app/reports,wewillcreateanewScalaclasscalledReportBuilder.scala.

YourReportBuilder.scalafileshouldhavethefollowingcode:

packagereports

objectReportBuilder{

privatevarreportCache:scala.collection.Map[String,Boolean]=

newscala.collection.mutable.HashMap[String,Boolean].empty

defgenerateCompileFileName(jrxml:String):String=

"/tmp/report_"+jrxml+"_.jasper"

defcompile(jrxml:String){

if(reportCache.get(jrxml).getOrElse(true)){

JasperCompileManager.compileReportToFile(new

File(".").getCanonicalFile+"/app/reports/"+jrxml,

generateCompileFileName(jrxml))

reportCache+=(jrxml->false)

}

}

deftoPdf(jrxml:String):ByteArrayInputStream={

try{

valos:OutputStream=newByteArrayOutputStream()

valreportParams:java.util.Map[String,Object]=new

java.util.HashMap()

valcon:Connection=DriverManager.getConnection

("jdbc:mysql://localhost/RWS_DB?user=root&password

=&useUnicode=true&useJDBCCompliantTimezoneShift

=true&useLegacyDatetimeCode=false&serverTimezone=UTC")

compile(jrxml)

valjrprint:JasperPrint=JasperFillManager.fillReport

(generateCompileFileName(jrxml),reportParams,con)

valexporter:JRPdfExporter=newJRPdfExporter()

exporter.setExporterInput(newSimpleExporterInput(jrprint))

exporter.setExporterOutput

(newSimpleOutputStreamExporterOutput(os));

exporter.exportReport()

newByteArrayInputStream

((os.asInstanceOf[ByteArrayOutputStream]).toByteArray())

}catch{

casee:Exception=>thrownewRuntimeException(e)

}

}

}

Firstofall,wearesettingatemporarydirectorytostoretheJaspercompiledfilesinthegenerateCompileFileNamefunction.Asyoucansee,wearestoringthecompiledreportsat/tmp/.Ifyoudon'tuseLinux,youwillneedtochangethispath.

Next,wehavethecompilefunction,whichreceivesaJRXMLreportinparameter.ThereisareportcacheMapobjecttoperformanon-demandcachefortheJasperfiles.Thismaphasthe

JRXMLreport,isthekeyasaBooleanfile.Thissolutionallowsyoutocompilereportsondemand.

Finally,wehavethetoPdffunctionthatwillreceivethejrxmlfunctionandcompilethereportthatisneeded.ThisfunctionusesDriverManagertogettheSQLconnectioninordertosendtheconnectiontotheJasperengine.Finally,thereisthefill,processmanagedbyJasperFillManager,whichwillreceivetheJasperfileandreportsparameters(forus,anemptymap)andtheSQLconnection.

Afterfillingthereportwithdatafromdatabase,wecanexportthereportinPDFusingtheJRPdfExportercommand.Asthisisagenericfunction,wewillreturnaByteArrayInputStream,whichisanin-memorystreamstructure.

Now,thenextstepistochangeourcontrollersinordertobeabletogeneratereportsforproducts,reviews,andimages.

AddingthereporttotheproductcontrollerWewillneedtochangetheproductcontrollerinordertoexposethenewreportfunction.

YourProductController.scalafile,afteraddingthereportfunction,shouldlooksomethinglikethis:

@Singleton


service:IProductService)extendsControllerwithI18nSupport{

//...restofthecontrollercode...

defreport()=Action{

importplay.api.libs.concurrent.

Execution.Implicits.defaultContext

Ok.chunked(Enumerator.fromStream(

ReportBuilder.toPdf("Products.jrxml")))

.withHeaders(CONTENT_TYPE->"application/octet-stream")

.withHeaders(CONTENT_DISPOSITION->"attachment;

filename=report-products.pdf"

)

}

}

Righthere,wehaveanewfunctioncalledreport.WewillneedtouseourReportBuildermethodpassingtheProducts.jrxmlasparameter.WeareusingtheOk.chunkedfunctioninordertobeabletostreamthereporttothebrowser.Wearealsosettingsomeresponseheaders,suchasthecontenttypeandthenameofthefile,whichwillbereportedtoproducts.pdf.

Now,wewillapplythesamecodetothereviewandimagecontrollers.

AddingthereporttothereviewcontrollerNowisthetimetocreatethereportfunctionforthereviewcontroller.Herewego.

YourReviewController.scalafile,afteraddingareportfunction,shouldlooksomethinglikethis:

@Singleton







defreport()=Action{




ReportBuilder.toPdf("Reviews.jrxml")))



filename=report-reviews.pdf")

}

}

Wehavethesamelogichereaswehavefortheproductcontroller.Themaindifferenceisthejrxmlfileandthefilenameresponseheader.Now,wecanmovetothelastcontroller--theimagecontroller.

AddingthereporttotheimagecontrollerFinally,wewillapplythesamelogichereaswedidfortheproductandreviewcontroller,butnowitistimetochangetheimagecontroller.

YourImageController.scalafile,afteraddingreportfunction,shouldlooksomethinglikethis:

@Singleton







defreport()=Action{




ReportBuilder.toPdf("Images.jrxml")))



filename=report-images.pdf")

}

}

Alright,wehavefinishedallthecontrollers.However,wewillneedtoconfigureroutes,otherwise,wewon'tbeabletocallthecontrollers--thisisthenextstep.

Routes-addingnewreportroutesNow,wewillneedtoaddthenewroutesforthereports.Forthat,wewilledittheconf/routesfile,asfollows:

GET/reportscontrollers.HomeController.reports

#

#Reports

#

GET/product/reportcontrollers.ProductController.report

GET/review/reportcontrollers.ReviewController.report

GET/image/reportcontrollers.ImageController.report

Wearedonewithroutesnow,andweneedtochangetheUIinordertoexposethenewreportfunctionality.Wewillcreateanewviewcontainingallreports,and,forthesakeofease,wewillalsoaddabuttonforeachresourceUI(product,review,andimage).

NewcentralizedreportsUIWewillneedtocreateanewviewatReactiveWebStore/views/reports_index.scala.html.

Yourreports_index.scala.htmlfileshouldlooksomethinglikethis:

@()(implicitflash:Flash)

@main("Reports"){

<ahref="/product/report"><imgheight="42"width="42"

src="@routes.Assets.at("images/product.png")">Products

Report</a><BR>

<ahref="/review/report"><imgheight="42"width="42"

src="@routes.Assets.at("images/review.png")">ReviewsReport

</a><BR>

<ahref="/image/report"><imgheight="42"width="42"

src="@routes.Assets.at("images/image.png")">Images

Report</a><BR>

}

Sohere,wewillbasicallylistallresources--product,review,andimagesandlinktherelativecontrollers,andwhentheuserclicksontherespectivelinkaPDFreportwillbedownloaded.Nowweneedtoediteachresource(product,image,andreview)viewinordertoaddalinkforthereportsthereaswell.

AddingthereportbuttonforeachviewLet'sedittheproductviewfirst.

Yourproduct_index.scala.htmlfileshouldlooksomethinglikethis:


@main("Products"){

//...restoftheuicode...

<p>

<ahref="@routes.ProductController.blank"class="btnbtn-

success">

<iclass="icon-plusicon-white"></i>AddProduct</a>

<ahref="@routes.ProductController.report"class="btnbtn-

success">

<iclass="icon-plusicon-white"></i>ProductsReport</a>

</p>

}

Asyoucanseehere,weaddedanewbuttonpointingtothenewreportfunction.WewillneedtodothesameforthereviewandtheimageUI.

Yourreview_index.scala.htmlfileshouldlooksomethinglikethis:


@main("Reviews"){

//...restoftheuicode...

<p>

<ahref="@routes.ReviewController.blank"class="btnbtn-

success"><iclass="icon-plusicon-white"></i>AddReview</a>

<ahref="@routes.ReviewController.report"class="btnbtn-

success"><iclass="icon-plusicon-white"></i>ReviewReport</a>

</p>

}

Nowwecanaddthefinalbuttontotheimageview.

Yourimage_index.scala.htmlfileshouldlooksomethinglikethis:


@main("Images"){

//...restoftheuitemplate...

<p>

<ahref="@routes.ImageController.blank"class=

"btnbtn-success"><iclass="icon-plusicon-white"></i>Add

Image</a>

<ahref="@routes.ImageController.report"class=

"btnbtn-success"><iclass="icon-plusicon-white"></i>

ImagesReport</a>

</p>

}

Allset!Nowwecanrun$activatorrunandseethenewUIandreportbuttons.Goto

http://localhost:9000/:

Ifyougotohttp://localhost:9000/reports,orclickonReports,youwillseethefollowing:

That'sit!WehaveallthereportsworkingonthePlayframeworkapplication.

SummaryInthischapter,youlearnedhowtocreatecustomreportsusingJaspersoftStudioandJasperReports.Additionally,youalsochangedyourapplicationinordertointegratethePlayframeworkandJasperReports.

Inthenextchapter,youwilllearnhowtousetheAkkaframework.Wewillcontinuebuildingourapplicationandembracetheactormodelforanewkillerfeatureforyourapplication.

Chapter8.DevelopingaChatwithAkkaInthepreviouschapters,wepersisteddataintoMySQLusingSlickandwrotePDFreportsusingJasperreports.NowwewilladdmorefeaturesinourappusingAkka.

Inthischapter,youwilllearnhowtocreateActorsusingtheAkkaframework.WewilluseActorsincombinationwiththePlayframeworkandWebSocketsinordertohaveachatcapability.

Wewillcoverthefollowingtopicsinthischapter:

UnderstandingtheActormodelActorsystems,Actorrouting,anddispatchersMailboxes,Actorconfiguration,andpersistenceCreatingourChatApplicationTestingourActors

AddingthenewUIintroductiontoAkkaAkka(http://akka.io/)isaframeworktobuildconcurrent,distributed,andresilientmessage-drivenapplicationsinScala,Java,and.NET.BuildingapplicationswithAkkahasseveraladvantages,whichareasfollows:

Highperformance:Akkadeliversupto50millionmessagespersecondonacommodityhardwarehaving~2.5millionActorsperGBofRAM.Resilientbydesign:Akkasystemshaveself-healingpropertiesforlocalandremoteActors.Distributedandelastic:Akkahasallthemechanismstoscaleyourapplication,suchascluster,loadbalancing,partitioning,andsharding.AkkaletsyougroworshrinkyourActorsondemand.

TheAkkaframeworkprovidesgoodabstractionsforconcurrent,asynchronous,anddistributedprogramming,suchasActors,Streams,andFutures.Thereareplentyofgreatsuccesscasesinproduction,suchasBBC,Amazon,eBay,Cisco,TheGuardian,Blizzard,Gilt,HP,HSBC,Netflix,andsomanyothers.

Akkaisatrulyreactiveframeworkbecauseeverything,inthesenseofsendingandreceivingmessagestoActors,islockless,non-blockingIO,andasynchronous.

http://akka.io/

IntroductiontotheActormodelThekeyforconcurrencyprogrammingistoavoidasharedmutablestate.Asharedstateoftenrequireslocksandsynchronization,whichmakesyourcodelessconcurrentandmorecomplex.Actorssharenothing;theyhaveinternalstate,buttheydon'tsharetheirinternalstate.

Actorshavelocationtransparency;theycanruninalocalorremotesystemandacluster.It'salsopossibletomixlocalandremoteactors-thisisgreatforscalabilityandfitsperfectlyintoacloudenvironment.Actorscanrunanywhere,fromyourlocalbox,thecloud,bare-metaldatacenter,andLinuxcontainers.

WhatisanActor?Actorscanbealternativestothreads,callbacklisteners,singletonservices,EnterpriseJavaBeans(EJB),routers,loadbalancerorpool,andafinite-statemachine(FSM).TheActormodelconceptisnotnewatall;itwascreatedbyCarlHewittin1973.TheActormodelisheavilyusedinthetelecomindustryinrock-solidtechnologiessuchasErlang.ErlangandtheActormodelhadimmensesuccesswithcompaniessuchasEricssonandFacebook.

Actorshaveasimplewayofworking:

Unitofcodeorganization:ProcessingStorageCommunication

TheymanagetheinternalstatesTheyhaveamailboxTheycommunicatewithotheractorsusingmessagesTheycanchangethebehavioratruntime

MessageexchangeandmailboxesActorstalkwitheachotherviamessaging.Therearetwopatterns:oneiscalledaskandtheotheriscalledfireandforget.Bothmethodsareasynchronousandnon-blockingIO.WhenanActorsendsamessagetoanotherActor,itdoesnotsendthemessagedirectlytotheotherActor;itactuallysendsittotheActor'smailbox.

MessagesareenqueuedintheActormailboxinatime-orderedfashion.TherearedifferentmailboxesimplementationsinAkka.ThedefaultisFirstInFirstOut(FIFO)based.Thisisagooddefault;however,youmightneedadifferentalgorithm,whichisfineasyoucanchangethemailboxifyouneedto.Moredetailscanbefoundintheofficialdocumentation(http://doc.akka.io/docs/akka/2.4.9/scala/mailboxes.html#mailboxes-scala).ActorsliveinanActorsystem.YoucanhavemultipleActorsystemsinacluster:

AkkaencapsulatestheactorstateinmailboxanddecouplesitfromtheActorbehavior.TheActorbehavioristhecodeyouwillhaveinsideyourActor.YouwillneedtoseeActorsandAkkaasaprotocol.So,basically,youwillneedtodefinehowmanyActorsyouwillhaveandwhateachActorwilldointhesenseofcode,responsibility,andbehavior.TheActorsystem

http://doc.akka.io/docs/akka/2.4.9/scala/mailboxes.html#mailboxes-scala

hasActorsandsupervisors.SupervisorsareoneoftheAkkamechanismstodeliverfaulttoleranceandresiliency.SupervisorstakecareoftheActorinstances,andtheycanrestart,kill,orcreatemoreActorsasneeded.

TheActormodelisgreatforconcurrencyandscalability;however,likeeverysinglethingincomputerscience,therearetradeoffsandcons.Forinstance,Actorsrequireanewmindsetandadifferentwayofthinking.

Thereisnosilverbullet.Onceyouhaveyourprotocol,itmightbehardtoreuseyourActorsoutsideyourprotocol.Ingeneral,Actorscanbehardertocompose,ascomparedtoobject-orientedclassesorfunctionsinFunctionalProgramming,forinstance.

CodingactorswithAkkaLet'stakealookatthefollowingActorcodeusingtheAkkaframeworkandScala:

importakka.actor._

caseobjectHelloMessage

classHelloWorldActorextendsActor{

defreceive={

caseHelloMessage=>sender()!"HelloWorld"

casea:Any=>sender()!"Idon'tknow:"+a+"-Sorry!"

}

}

objectSimpleActorMainAppextendsApp{

valsystem=ActorSystem("SimpleActorSystem")

valactor=system.actorOf(Props[HelloWorldActor])


importakka.util.Timeout

importakka.pattern.ask

importscala.concurrent.Await

implicitvaltimeout=Timeout(20seconds)

valfuture=actor?HelloMessage

valresult=Await.result(future,

timeout.duration).asInstanceOf[String]

println("Actorsays:"+result)

valfuture2=actor?"Cobol"

valresult2=Await.result(future2,

timeout.duration).asInstanceOf[String]

println("Actorsays:"+result2)

system.terminate()

}

IfyourunthisAkkacodeonsbtinyourconsole,youwillseeanoutputsimilartothis:

$sbtrun

Let'stakeacloserlookatthisAkkacodewejustwrote,inwhichwedefinedaScalaclasscalledHelloWorldActor.InorderforthisclassbeanActor,wewillneedtoextendActor.Actorsarereactivebydefault,whichmeansthattheyarewaitingtoreceivemessagestoreacttothemessages.Youwillneedtocodeyourbehaviorinaneventloop.InAkka,thisisdonebycodingthereceivefunctionwithapatternmatcherinScala.

Thepatternmatcherwilldefinewhattheactorcando.Youwillneedtocodeallthepossiblekindsofmessagesyouwantthatactortohandle.AsImentionedearlier,youwillneedtohaveaprotocol;soyourprotocolhasamessagecalledHelloMessage.It'sacommonpracticeinAkkatouseScalaobjectsasmessages.However,youcanpassprettymuchalltypesasmessages.It'sevenpossibletosendcaseclasseswithparameters.

Alright,wehaveourprotocol,whichisourActors,andthemessagestheycanexchange.NowwewillneedtocreateanActorsystemandstartourapplication.Asyoucansee,wewillusetheActorSystemobjecttocreateanActorsystem.Actorsystemsneedtohaveaname,whichcanbeanystringyoulike,aslongasitcontainsanyletter[a-z,A-Z,0-9]andnon-leading'-'or'_'.

Aftercreatingthesystem,youcancreateActors.ThesystemhasafunctioncalledactorOf,whichcanbeusedtocreateActors.YouwillneedtouseaspecialobjectcalledPropsandpasstheactorclass.Whydoweneeditthisway?It'sbecauseAkkamanagestheActorstate.YoushouldnottrytomanagetheActorinstancebyyourself.Thisisdangerousbecauseyoucanbreakreferentialtransparencyandyourcodemightnotwork.

Forthiscode,weareusingtheaskpattern.WewillusethistosendmessagestotheActor,andwewanttoknowwhattheActorwillreturn.Akkadoeseverythinginanasyncandnon-blockingway,asmentionedpreviously.However,sometimesyouwanttogettheanswernowandthen,unfortunately,youwillneedtoblock.

Inordertogettheanswernow,wewillneedtodefineatimeoutandusetheAwaitobject.WhenyousendamessagetoanActorusing?(theaskpattern),AkkawillreturnaFutureforyou.Then,youcanpasstheFuturewithatimeouttoAwait,andiftheanswercomesbackbeforethetimeout,youwillhavetheresponsefromtheActor.

Again,weareblockingherebecausewewanttogettheanswernow,andweareoutsidetheActorsystem.KeepinmindthatwhenanActortalkswithanotherActorinsidetheActorsystem,itshouldnotblockever.SobecarefulwiththeusageofAwait.

Anotherimportantthinginthiscodeisthatthesender()methodinsideoftheActorreceivesafunction.ThismeansthatyouwanttogetthereferenceoftheActorwhosendsthemessagetoyou.Asweareperformingsender()!method,wearesendingananswerbacktothecaller.Thesender()functionisanAkkaabstractiontodealwithresponsemessagestootherActorsorfunctioncallers.

Wealsohaveanothercase,withAny,whichmeansallothermessageswillbehandledbythat

casecode.

TheaskpatternisonewaytosendmessagestoActors.ThereisanotherpatterncalledFireAndForget"!".Fireandforgetwillsendamessageandwillnotblockandwaitfortheanswer.So,thereisnoanswer-inotherwords,Unit.

Let'slookatsomecodewiththeFireAndForgetmessageexchange:

importakka.actor._

objectMessage

classPrinterActorextendsActor{

defreceive={

casea:Any=>

println("Print:"+a)

}

}

objectFireAndForgetActorMainAppextendsApp{


valactor=system.actorOf(Props[PrinterActor])

valvoidReturn=actor!Message

println("Actorsays:"+voidReturn)

system.terminate()

}

Ifyourunthiscodewith$sbtrun,youwillseeanoutputasfollows:

Here,wehaveaPrinterActormethod,whichacceptsprettymuchanythingandprintsontheconsole.Then,wewillcreateanActorsystemandjustsendamessagetoourActorwiththefireandforgetpattern,a.k.a"!",andasyoucansee,wewillreceiveUnit;finally,wewillawaittheshutdownoftheActorsystemusingtheterminateoption.

ActorroutingAkkaprovidesroutingfunctionality.ThisisusefulfromabusinesspointofviewbecauseyoucanroutetotherightActorinthesenseofbusinesslogicandbehavior.Forarchitecture,wecanusethisasloadbalancingandroutemessagestomoreActorstoachievefaulttoleranceandscalability.

Akkahasseveraloptionsforrouting,whichareasfollows:

RoundRobin:ThisisarandomlogictoeverydifferentActoronthepool.SmallestMailbox:ThissendsthemessagetotheActorwithfewermessages.ConsistentHashing:ThispartitionstheActorsperhashID.ScatterGather:Thissendsmessagetoallactors,andthefirsttoreplywins.TailChopping:Thissendstoarouterandomly,andifareplydoesn'tcomebackinasecond,itchoosesanewrouteandsendsagain,andsoon.

Let'sseethefollowingcodeinpractice:

importakka.actor._

importakka.routing.RoundRobinPool

classActorUpperCasePrinterextendsActor{

defreceive={

cases:Any=>

println("Msg:"+s.toString().toUpperCase()+"-"+

self.path)

}

}

objectRoutingActorAppextendsApp{


valactor:ActorRef=system.actorOf(

RoundRobinPool(5).props(Props[ActorUpperCasePrinter]),name=

"actor")

try{

actor!"works1"

actor!"works2"

actor!"works3"

actor!"works4"

actor!"works5"

actor!"works6"

}catch{

casee:RuntimeException=>println(e.getMessage())

}

system.terminate()

}

Ifyourunthiscodeinsbtdoing$sbtrun,youwillgetanoutputasfollows:

So,herewehaveanActorUppercasePrinterfunctionthatprintswhateveritreceivesandcallsthetoStringfunction,andthentoUpperCase.Finally,italsoprintstheself.pathActor,whichwillbetheaddressoftheActor.Actorsarestructuredinahierarchicalstructure,similartoafilesystem.

TherearemultiplewaystouseAkka-Akkasupportscodeorconfiguration(application.conffile).Here,wearecreatingaround-robinpoolactorthathasfiveroutes.WearepassingthetargetActortotherouterthatwillbeourprinterActor.

Asyoucansee,whenwesendmessagesusingthefireandforgetpattern,everymessageisdeliveredtoadifferentActor.

PersistenceAkkaworksonmemory.However,itispossibletousepersistence.PersistenceisstillkindofexperimentalinAkka.However,itisstable.Forproduction,youcanuseadvancedpersistenceplugins,suchasApacheCassandra.Forthesakeofdevelopmentandeducation,wewilluseGoogleleveldbinourfilesystem.Akkahasmultiplepersistenceoptions,suchasviewsandpersistentActors.

Let'stakealookatapersistentactorusingtheGoogleleveldbandfilesystem:

importakka.actor._

importakka.persistence._


classPersistenceActorextendsPersistentActor{

overridedefpersistenceId="sample-id-1"

varstate:String="myState"

varcount=0

defreceiveCommand:Receive={

casepayload:String=>

println(s"PersistenceActorreceived${payload}(nr=

${count})")

persist(payload+count){evt=>

count+=1

}

}

defreceiveRecover:Receive={

case_:String=>

println("recover...")

count+=1

}

}

objectPersistentViewsAppextendsApp{


valpersistentActor=

system.actorOf(Props(classOf[PersistenceActor]))

importsystem.dispatcher

system.scheduler.schedule(Duration.Zero,2.seconds,

persistentActor,"scheduled")

}

Executingthe$sbtruncommandwillgiveyouthefollowingoutput:

Ifyourunthiscodewith$sbtrun,andstopandrunagain,youwillseethedataisbeingstoredandrecoveredeverytimeyoustopandstartagain.

Asyoucansee,yourActorneedstoextendPersistentActorinordertohavepersistencesupport.YouwillalsoneedtoprovideapersistenceID.

Here,youwillneedtoimplementtworeceivefunctions.Oneisforcommands(alsoknownasmessages),andtheotheroneisforrecovery.Thecommand'sreceiveloopwillbeactivatedwhenthisActorreceivesmessages,whiletherecoveronewillbeactivatedwhentheActorbootsupandwillreadthepersistentdatafromthedatabase.

So,thisActorherehasacountertocounteachmessageitreceives,andprintseverymessageitgetsontheconsole.That'sit;asyoucansee,itisprettysimple.Inordertousethisfunctionality,youwillalsoneedtoconfigureyourapplication.conf.

Yourapplication.conffileshouldlooksomethinglikethis:

akka{

system="SimpleActorSystem"

remote{

log-remote-lifecycle-events=off

netty.tcp{

hostname="127.0.0.1"

port=0

}

}

}

akka.cluster.metrics.enabled=off

akka.persistence.journal.plugin=

"akka.persistence.journal.leveldb"

akka.persistence.snapshot-store.plugin=

"akka.persistence.snapshot-store.local"

akka.persistence.journal.leveldb.dir="target/persistence/journal"

akka.persistence.snapshot-store.local.dir=

"target/persistence/snapshots"

#DONOTUSETHISINPRODUCTION!!!

#Seealsohttps://github.com/typesafehub/activator/issues/287

akka.persistence.journal.leveldb.native=false

So,herewearedefiningasimpleAkkasystem(localmode),andweareconfiguringthepersistenceforGoogleleveldb.Asyoucansee,wewillneedtoprovideapathforpersistence,andthispathmustexistontheOS.

Asweareusinganadditionalfunctionality,wewillalsoneedtochangebuild.sbtinordertoimportalljarsthatwewillneedinthesenseofAkka,persistence,andleveldb.

Yourbuild.sbtfileshouldlooksomethinglikethis:

//restofthebuild.sbtfile...

valakkaVersion="2.4.9"

libraryDependencies+="com.typesafe.akka"%%"akka-actor"%

akkaVersion

libraryDependencies+="com.typesafe.akka"%%"akka-kernel"%

akkaVersion

libraryDependencies+="com.typesafe.akka"%%"akka-remote"%

akkaVersion

libraryDependencies+="com.typesafe.akka"%%"akka-cluster"%

akkaVersion

libraryDependencies+="com.typesafe.akka"%%"akka-contrib"%

akkaVersion

libraryDependencies+="com.typesafe.akka"%%"akka-persistence"%

akkaVersion

libraryDependencies+="org.iq80.leveldb"%"leveldb"%"0.7"

libraryDependencies+="org.iq80.leveldb"%"leveldb-api"%"0.7"

libraryDependencies+="org.fusesource.leveldbjni"%"leveldbjni"%

"1.8"

libraryDependencies+="org.fusesource.leveldbjni"%"leveldbjni-

linux64"%"1.8"

libraryDependencies+="org.fusesource"%"sigar"%"1.6.4"

libraryDependencies+="org.scalatest"%"scalatest_2.11"%"2.2.6"

That'sit.That'sallweneedtopersisttheActor'sstate.

Note

Akkahaswaymorefunctionalities.Formore,checkoutthedefaultdocumentationathttp://doc.akka.io/docs/akka/2.4/scala.html?_ga=1.12480951.247092618.1472108365.

http://doc.akka.io/docs/akka/2.4/scala.html?_ga=1.12480951.247092618.1472108365

CreatingourchatapplicationNowthatweknowAkkabetter,wewillcontinuetodevelopourapplication.AkkahasagreatintegrationwiththePlayframework.WewilluseActorswiththeAkkaandPlayframeworkrightnow.Let'sbuildasimplechatfeatureforourapp.WewillchangethecodetoaddanewUIand,usingtheAkkatestkit,wewilltestoutactors.

ThePlayframeworkalreadyincludesAkkaontheclasspathforus,sowedon'tneedtoworryaboutit.However,wewillneedtoaddtheAkkatestkitdependencytothebuild.sbtfileinordertohavetheclassesinourclasspath.

Yourbuild.sbtshouldlooksomethinglikethis:

//restofthebuild.stb...


"com.typesafe.akka"%%"akka-testkit"%"2.4.4"%Test,

//restofthedeps...

)

//restofthebuild.stb...

Okay,nowyoucangototheconsoleandtype$activator,$reload,andthen$compile.Thiswillforcesbttodownloadthenewdependency.

NowwewillneedtocreateapackagecalledActors.ThispackageneedstobelocatedatReactiveWebStore/app/.WewillstartcreatinganActorHelperutilityobjectinordertohaveagenericfunctionfortheaskpatternthatwesawearlier.ItisanActorhelpergenericaskpatternutility.

YourActorHelper.scalafileshouldlooksomethinglikethis:

packageactors

objectActorHelper{

importplay.api.libs.concurrent.

Execution.Implicits.defaultContext


importakka.pattern.ask

importakka.actor.ActorRef

importakka.util.Timeout



defget(msg:Any,actor:ActorRef):String={

implicitvaltimeout=Timeout(5seconds)

valresult=(actor?msg).mapTo[String].map{result=>

result.toString}

Await.result(result,5.seconds)

}

}

TheActorHelperhasjustonefunction:get.ThisfunctionwillgetananswerfromanyActorgiveninanymessage.However,asyoucansee,wehaveatimeoutoffiveseconds.Ifthe

resultdoesnotcomebackinthistime,anexceptionwillberaised.

Inthiscode,wearealsomappingtheActorresulttoaStringcallingthetoStringfunctionintheresultfuture.Thisisnotalotofcode;however,therearelotsofimports,anditmakesthecodecleanerandwecangetanswersfromActorswithlesscodeandfewerimports.

ThechatprotocolNowwewillneedtodefineourprotocol.Forthisfunctionality,wewillneedthreeActors.TheActorsthatwecreatewillbeasfollows:

ChatRoom:ThiswillhaveareferenceforallusersinthechatroomChatUser:Thiswillhaveoneinstanceperuser(activebrowser)ChatBotAdmin:ThissimpleBotAdminwillprovidestatsaboutthechatroom

ChatUserActorwillneedtojoinJoinChatRoomobjectinordertostartchatting.ChatUserActorwillalsoneedtosendmessagestoChatMessageclasstotheChatRoomActorthatwillbroadcastmessagestoallusers.TheChatBotAdminwillgetareportfromGetStatsobjectfromChatRoomActor.

Let'sstartcodingthisprotocol.First,wewillneedtodefinethemessagesthatwillbeexchangedbetweentheseActors,asshowninthefollowingpieceofcode:

packageactors

caseclassChatMessage(name:String,text:String)

caseclassStats(users:Set[String])

objectJoinChatRoom

objectTick

objectGetStats

Asyoucanseehere,wehaveaChatMessageclasswithanameandatext.Thiswillbethemessageeachuserwillsendonthechat.Then,wewillhaveastatsclass,whichhasasetofusers--thiswillbealltheusersloggedintothechatapplication.

Finally,wehavesomeactionmessages,suchasJoinChatRoom,Tick,andGetStats.So,JoinChatRoomwillbesentbyChatUserActortoChatRoomActorinordertojointhechat.TickwillbeascheduledmessagethatwillhappenfromtimetotimeinordertomakeChatBotAdminsendstatsaboutthechatroomtoallloggedusers.GetStatsisthemessagethatChatBotAdminActorwillsendtoChatRoomActorinordertogetinformationaboutwhoisintheroom.

Let'scodeourthreeactorsnow.

TheChatRoomActor.scalafileshouldlooksomethinglikethis:

packageactors

importakka.actor.Props

importakka.actor.Terminated

importakka.actor.ActorLogging

importakka.event.LoggingReceive

importakka.actor.Actor


importplay.libs.Akka

importakka.actor.ActorSystem

classChatRoomActorextendsActorwithActorLogging{

varusers=Set[ActorRef]()

defreceive=LoggingReceive{

casemsg:ChatMessage=>

usersforeach{_!msg}

caseJoinChatRoom=>

users+=sender

contextwatchsender

caseGetStats=>

valstats:String="onlineusers["+users.size+"]-users["

+users.map(a=>a.hashCode().mkString("|")+"]"

sender!stats

caseTerminated(user)=>

users-=user

}

}

objectChatRoomActor{

varroom:ActorRef=null

defapply(system:ActorSystem)={

this.synchronized{

if(room==null)room=system.actorOf(Props[ChatRoomActor])

room

}

}

}

ChatRoomActorhasavarcalledusers,whichisasetofActorRef.ActorRefisagenericreferencetoanyactor.Wehavethereceivefunctionwiththreecases:ChatMessage,JoinChatRoom,andGetStats.

AJoinChatRoomwillbesentbytheChatUserActormethodinordertojointheroom.Asyoucansee,wearegettingtheActorRefmethodfromthesenderActorusingthesender()function,andweareaddingthisreferencetothesetofusers.Inthisway,thesetofActorRefrepresentstheonlinelogged-inusersinthechatroomrightnow.

TheothercaseiswiththeChatMessagemethod.Basically,wewillbroadcastthemessagetoallusersinthechat.Wedothisbecausewehavethereferenceforallactorsinusers.Then,wewillcalltheforeachfunctioninordertoiterateallusersonebyone,andthenwewillsendthemessageusingFireAndForget"!"toeachuserActorrepresentedbytheoperatorunderscore_.

TheGetStatscasecreatesastringwithallchatroomstats.Fornow,thestatsarejustthenumberofonlineusers,whichiscomputedbycallingthesizefunctionontheusersobject.WearealsoshowingallthehashcodesthatidentifyallActorsloggedin,justforfun.

That'sourChatRoomActorimplementation.Asyoucansee,itishardtotalkaboutoneActorwithoutdescribingtheother,astheprotocolwillalwaysbekindofcoupled.YoumightalsobewonderingwhywehaveacompanionobjectfortheChatRoomActormethod.

ThisobjectistoprovideaneasywaytocreateActorinstances.Wearecreatingasingleroomforourdesign;wedon'twanttohavemultiplechatrooms,sothat'swhywewillneedto

controlthecreationoftheroomActor.

Iftheroomisnull,wewillcreateanewroom;otherwise,wewillreturnthecachedinstanceoftheroomthatwealreadygotinthememory.WewillneedaninstanceoftheActorsysteminordertocreateactors,sothat'swhywearereceivingthesystemontheapplyfunction.TheapplyfunctionwillbecalledwhensomeonewritesacodelikeChatRoomActor(mySystem).

Now,let'smovetotheChatUserActorimplementation.

TheChatUserActor.scalafileshouldlooksomethinglikethis:

packageactors







classChatUserActor(room:ActorRef,out:ActorRef)extendsActorwith

ActorLogging{

overridedefpreStart()={

room!JoinChatRoom

}


caseChatMessage(name,text)ifsender==room=>

valresult:String=name+":"+text

out!result

case(text:String)=>

room!ChatMessage(text.split(":")(0),text.split(":")(1))

caseother=>

log.error("issue-notexpected:"+other)

}

}

objectChatUserActor{

defprops(system:ActorSystem)(out:ActorRef)=Props(new

ChatUserActor(ChatRoomActor(system),out))

}

ThisActorisalittlebiteasierthanthepreviousone.ChatUserActorreceives,asaparameter,theroomactorreferenceandalsoanoutactor.Theroomwillbeaninstanceoftheroomthattheuserwillusetocommunicatewithotherusers.TheActorRefmethodcalledoutisthePlayframeworkActorresponsibleforsendingtheanswerbacktothecontrollersandUI.

Weprettymuchjusthavetwocases:onewherewereceiveaChatMessageandtheotheristheChatUserActorsmethodinthechatroom.So,wewilljustneedtosendbacktotheUIusingtheoutActor.That'swhythereisafireandforgetmessagefortheoutActorwitharesult.UsinganewActormodelcanbedangerous,pleasereadmoreathttp://doc.akka.io/docs/akka/current/scala/actors.html.

ThereisanothercasethatjustreceivesastringthatwillbethemessagefromthatActoritself.RememberthateachActorrepresentsauserandabrowserfullofduplexconnectionsvia

http://doc.akka.io/docs/akka/current/scala/actors.html

WebSockets.Don'tworryaboutWebSocketsnow;wewillcoveritinmoredetaillaterinthischapter.

Forthiscasefunction,wearesendingtheChatMessagemethodtotheroom.Wewillsplitthemessagesintwoparts:theusernameandthetext,whichissplitby:.

Here,wealsohaveacompanionobjectforthesakeofgoodpractice.So,youcancallChatUserActor,passingtheActorsystemandacurriedparameterfortheoutactor.

Now,wewillmovetothelastActor:theBotAdminActor,whichshouldlooksomethinglikethis:

packageactors








classChatBotAdminActor(system:ActorSystem)extendsActorwith

ActorLogging{



valroom:ActorRef=ChatRoomActor(system)

valcancellable=system.scheduler.schedule(0seconds,

10seconds,self,Tick)

overridedefpreStart()={

room!JoinChatRoom

}


caseChatMessage(name,text)=>Unit

case(text:String)=>room!ChatMessage(text.split(":")(0),

text.split(":")(1))

caseTick=>

valresponse:String="AdminBot:"+ActorHelper.get

(GetStats,room)

sender()!response

caseother=>

log.error("issue-notexpected:"+other)

}

}

objectChatBotAdminActor{

varbot:ActorRef=null

defapply(system:ActorSystem)={

this.synchronized{

if(bot==null)bot=system.actorOf(Props

(newChatBotAdminActor(system)))

bot

}

}

}

Asyoucansee,thisActorreceivesthereferenceofthechatroomasaparameter.Usingthe

Actorsystem,itgetsthereferenceofthechatroomActor.ThisActorreceivesanActorSystemmessagebynow.

UsingtheActorsystemvariablecalledsystem,wewillalsoscheduleaTickforthisActorforeverytenseconds.Thistime,thewindowintervalwillbethetimeinwhichthebotwillnotifythechatroomaboutthecurrentstatus.

WewillalsooverridethepreStartfunction.AkkawillcallthisfunctionwhentheActoriscreatedontheactorsystem.Thisimplementationwillsendamessagetotheroom,whichisJoinChatRoom.

LikeallActors,thereisthereceivefunctionimplementation.FirstcasewithChatMessageisreturningUnit.Ifyouwanttomakethisbotrespondtopeople,removeUnitandwritetheproperScalacodeasyouwish.

Inthesecondcase,wewillhavetheStringmessagethatwillbesenttothechatroom.Finally,afterthiscase,wewillhavetheTickmethod,whichwillappeareverytenseconds.So,wewillusetheActorHelpertogetthestatsfromtheroom,andthenwewillsendastringmessagewiththeinformationabouttheroom.Thiswilltriggerthesecondcaseandbroadcastthemessagetothewholeroom.

Finally,wehaveacompanionobject.Wedon'twanttohavetwoinstancesofthebot,whichiswhywewillcontrolthisobjectcreationbydesign.We'redonewiththeactorsimplementations.Next,wewillneedtoworkanewcontrollerforthechatactors.

ThechatcontrollerWewillneedtocreateanewcontroller.ThiscontrollerwillbelocatedatReactiveWebStore/app/controllers.

ImplementingthechatcontrollerChatController.scalashouldlooksomethinglikethis:

packagecontrollers


importakka.stream.Materializer


importplay.api._

importplay.api.mvc._

importplay.api.libs.streams._

importactors.ChatUserActor

importactors.ChatBotAdminActor

@Singleton

classChatController@Inject()(implicitvalsystem:ActorSystem,

materializer:Materializer)

extendsController{



ChatBotAdminActor(system)

defindex_socket=Action{request=>

Ok(views.html.chat_index()(Flash(Map())))

}

defws=WebSocket.accept[String,String]{request=>

ActorFlow.actorRef(out=>ChatUserActor.props(system)(out))

}

}

TheChatControllermethodwilluseGoogleGuicetogetinjectedinstancesofActorSystemandanActormaterializerinstance.AmaterializerisneededbecauseitwillprovidetheinstanceoftheoutActorforeachuserinthesystem.

Asyoucansee,wewillcreateaninstanceoftheChatBotAdminmethodpassingthroughtheactorsystem,whichGoogleGuiceinjectedforus.Forthiscontroller,wewilljusthavetwofunctions:onefunctiontorenderthechatUI,andtheotheronetoservetheWebSocket.

ThePlayframeworkalreadyprovidesbuilt-inintegrationwithAkkaandWebSockets.So,wewilljustneedtousetheActorFlowmethodusingtheactorReffunctioninordertoobtainanoutActor.

Here,wewillcalltheChatUserActorcompanionobjectandcreateachatuserforthewebsocketpassingouttheActorsystemthecontrollerhas.Asyoucansee,thisreturnsWebSocket.accept,whichisafullduplexconnectionbetweenthewebbrowserandthebackend.

ConfiguringtheroutesNext,wewillneedtoexposeourcontrollerfunctionstotheUI.WewillneedtoaddmoreroutestotheReactiveWebStore/conf/routesfile:

routes

#

#AkkaandWebsockets

#

GET/chat/index_socketcontrollers.ChatController.index_socket

GET/chat/wscontrollers.ChatController.ws

Theroutesaredonenow.

WorkingontheUINow,itistimetocodeontheUIonboththeHTMLlayoutandtheWebSocketcodeinJavaScript.Wewillneedtocreateanewfile,locatedatReactiveWebStore/app/views.

Yourchat_index.scala.htmlfileshouldlooksomethinglikethis:

@()(implicitflash:Flash)

@main("Chat"){

<!DOCTYPEhtml>

<metacharset="utf-8"/>

<title>ChatRoom</title>

<scripttype="text/javascript">

varoutput;

varwebsocket=newWebSocket("ws://localhost:9000/chat/ws");

functioninit(){

output=document.getElementById("output");

websocket.onmessage=function(evt){

writeToScreen('<spanstyle="color:blue;">'+evt.data+

'</span>');

};

websocket.onerror=function(evt){

writeToScreen('<spanstyle="color:red;">ERROR:</span>'+

evt.data);

};

}

functiondoSend(message){

websocket.send(message);

}

functionwriteToScreen(message){

varpre=document.createElement("p");

pre.style.wordWrap="break-word";

pre.innerHTML=message;

$('#output').prepend(pre);

}

window.addEventListener("load",init,false);

</script>

<h3>Messages</h3>

<divid="output"style="width:800px;height:250px;overflow-y:

scroll;">

</div>

<divid="contentMessage">

<BR>

user:

<inputtype="text"name="txtUser"id="txtUser"/><BR><BR>

message:<inputtype="text"name="txtMessage"

id="txtMessage"/>

<BR>

<BR>

<ahref="#"class="btnbtn-success"

onclick="doSend(document.getElementById('txtUser').value+':'

+document.getElementById('txtMessage').value);">

<iclass="icon-plusicon-white"></i>SendMessage</a>

</div>

}

TheUIisverysimple.Thereisaninputtextforyoutoputyournameandthereisanotheroneforthetextmessageitself,andasendbutton.AsyoucanseeintheJavaScriptcode,thefirstthingthatwewilldoisopenaWebSocketconnectiontothews://localhost:9000/chat/wsURL.Then,wewillregistertheinitfunctiontorunoncethebrowserisready.

TheinitfunctioninJavaScriptwillcreatetwofunctionsforourWebSocket.OnefunctionwillrunwhenanyerroroccursandtheotherfunctionwillrunforeachmessageemittedbytheAkkabackend.

WewillhaveadoSendfunctioninJavaScriptinordertosendamessagetotheWebSocket.ThismessagewillbedeliveredtothecontrollerandthentotheAkkaactors.YoucanalsoseesomeJQueryandHTMLcodeinordertocreatenewelementsontheUI.Thisisdoneinordertodisplaythemessageinthechatroom.

OK,thereisonemorethingthatwewillneedtodo-addareferencetothechatUIonthemainpageofourapplication.

YourIndex.scala.htmlshouldlooksomethinglikethis:

@(message:String)(implicitflash:Flash)

@main("WelcometoReactiveWebStore"){

<divclass="row-fluid">

<BR>

<divclass="span12">


<divclass="span6">

<ahref="/product"><imgheight="42"width="42"

src="@routes.Assets.at("images/product.png")">Manage

Products</a><BR>

<ahref="/review"><imgheight="42"width="42"

src="@routes.Assets.at("images/review.png")">Manage

Reviews</a><BR>

<ahref="/image"><imgheight="42"width="42"

src="@routes.Assets.at("images/image.png")">Manage

Images</a><BR>

</div>

<divclass="span6">

<ahref="/reports"><imgheight="42"width="42"

src="@routes.Assets.at("images/reports.png")">Reports</a>

<BR>

<ahref="/chat/index_socket"><imgheight="42"width="42"

src="@routes.Assets.at("images/chat.png")">ChatRoom</a>

<BR>

</div>

</div>

</div>

</div>

}

WewillalsousetheopportunitytoimprovealittlebitoftheUIdesignusingTwitterBootstrapcolumndesign.Inthelastrow,youcanseeourlinktothechatUI.Now,wecanruntheapplicationandseeourchatworking.Run$activatorrun:

Asyoucansee,ournewchatUIlinkisthere.Now,let'shavefunwiththisnewfeature.Openfournewbrowsers(simulatefourdifferentusers),thengotothehttp://localhost:9000/chat/index_socketurlandlet'shavealittlechat.Youshouldseesomethingsimilartothis:

Almostdone.Ourchatfeatureworks;however,wewillneedtodomorethanjustafunctionalblackboxtestontheUI.Wewillneedunittests.Luckilyforus,wehavetheAkkatestkit,whichallowsustoeasilytestactors.

AddingAkkatestsWewillcreatethreemoretests:oneforeachactorthatwehave.TheyarelocatedatReactiveWebStore/test/.

ScalatestforAkkaActorChatUserActorSpec.scalashouldlooksomethinglikethis:

classOutActorextendsActor{

defreceive={

casea:Any=>Unit

}

}

classChatUserActorSpecextendsPlaySpec{

classActorsextendsTestKit(ActorSystem("test"))

"ChatUserActor"should{

"joinsthechatroomandsendamessage"innewActors{

valprobe1=newTestProbe(system)

valactorOutRef=TestActorRef[OutActor](Props[OutActor])

valactorRef=TestActorRef[ChatUserActor]

(ChatUserActor.props(system)(actorOutRef))

valuserActor=actorRef.underlyingActor

assert(userActor.context!=null)

valmsg="testUser:testmsg"

probe1.send(actorRef,msg)

actorRef.receive(msg)

receiveOne(2000millis)

}

}

}

TheAkkatestkitisverycoolasitallowsustotestactorswithaveryeasyDomainSpecificLanguage(DSL).It'spossibletochecktheActormailbox,theActorinternalstate,andsomuchmore.Thereisonetrickthatwewillneedtodobecauseweneedtoextendoneclass;inordertohavePlayworkingwiththeScalatest,wewillneedtousePlaySpec.However,wewillalsoneedtoextendoneclasstomaketheAkkatestkitwork,whichisTestKit.Wecan'textendbothatthesametime,butnoworries,thereisalwaysaworkaround.

Theworkaroundhereistocreateacaseclass,makethatcaseclassextendTestKit,andthenuseitinaspeccontext,thatis,inanewActor{}.

Here,wearecheckingifChatUserActorcanjointhechatroomproperly.ThisisdonebysimplycreatingtheActor,astheActorhasapreStartmethodthatwillauto-jointheroom.

WewillneedtocreateafakeimplementationoftheoutActorhere,whichiswhywehavetheOutActorimplementation.Wewillcreateaprobetotesttheactorsystem,andwewillalsouseaspecialfunctiontotesttheActors,calledTestActorRef.ThisabstractionprovidesawaytoaccesstheActor'sstateviaactorRef.underlyingActor,andthisisusefulbecauseyoucanchecktheActorinternalstatetovalidatethecode.TherestofthecodeisnormalAkkaandScalatestcode.Let'smovetothenexttest.

ChatroomActortestTheChatRoonActorSpec.scalafileshouldlooksomethinglikethis:

classChatRoomActorSpecextendsPlaySpec{

classActorsextendsTestKit(ActorSystem("test"))

"ChatRoomActor"should{

"acceptjoinsthechatrooms"innewActors{



valactorRef=TestActorRef[ChatRoomActor]

(Props[ChatRoomActor])

valroomActor=actorRef.underlyingActor

assert(roomActor.users.size==0)

probe1.send(actorRef,JoinChatRoom)


awaitCond(roomActor.users.size==2,100millis)

assert(roomActor.users.contains(probe1.ref))


}

"getstatsfromthechatroom"innewActors{





assert(roomActor.users.size==0)




probe1.send(actorRef,GetStats)

receiveOne(2000millis)

}

"andbroadcastmessages"innewActors{









valmsg=ChatMessage("sender","testmessage")

actorRef.receive(msg)

probe1.expectMsg(msg)

probe2.expectMsg(msg)

}

"andtrackusersrefandcounts"innewActors{









probe2.ref!PoisonPill


}

}

}

So,herewehavethesameconceptsastheothertest.However,wehavemoreusageoftheAkkatestkitDSL.Forinstance,weareusingexpectMsgontheprobetocheckifanActorreceivedaspecificmessage.WearealsousingawaitCondtochecktheActor'sinternalstateinanassertion.

NowisthetimetotestthelastActormethod.

ChatBotAdminActortestChatBotAdminActorSpec.scalafileshouldlooksomethinglikethis:

classChatBotAdminActorSpecextendsTestKit(ActorSystem("test"))

withImplicitSender

withWordSpecLikewithMatcherswithBeforeAndAfterAll{

"ChatBotAdminActor"should{

"beabletocreateBotAdminintheChatRoomandTick"in{


valactorRef=TestActorRef[ChatBotAdminActor](Props(new

ChatBotAdminActor(system)))

valbotActor=actorRef.underlyingActor

assert(botActor.context!=null)

awaitCond(botActor.room!=null)

}

}

}

Forthistest,wewillcheckiftheactorcontextwasnotnull,andalsoiftheroomwascreatedandtheschedulerwasalsonotnull.Allgoodtogo.

Alright,that'sit!Thisisthelastactortest.Nowwearecompletelydone.Youcanrunthistestwith$activatortest,or,ifyouprefertheactivator,thenuse"test-onlyTESTCLASSNAME"-Dsbt.task.forcegc=falsetorunaspecifictestcase.

SummaryInthischapter,youlearnedhowtoworkwithAkkaactorsandcreatedawebchatusingAkka,thePlayframework,andWebSockets.AkkaisareallypowerfulsolutionthatcanbeusedwithorwithoutthePlayframework.Additionally,youlearnedabouttheActormodel,mailboxes,routing,persistence,Akkaconfiguration,messagepatterns,andhowtowritecodewithactorsinScalaandPlay.

Inthenextchapter,youwilllearnmoreaboutREST,JSON,andhowtomodelaRESTAPI,aswellashowtocreateaScalaclientforyourRESTservices.

Chapter9.DesignYourRESTAPIInthepreviouschapter,weaddedanewchatfeatureinourappusingAkka.Ourwebapplicationisclosetotheend.ThischapterwilladdtheRESTAPIinourPlayframeworkapplication.

WewillalsocreateaScalaclientusingthewslibraryfromthePlayframeworkinordertocallourRESTAPI.Laterinthischapter,wewilladdSwaggersupportandembedtheSwaggerUIinourapp.


RESTandAPIdesignCreatingourAPIwithRESTandJSONCreatingaScalaclientAddingvalidationsAddingbackpressureAddingSwaggersupport

IntroductiontoRESTRepresentationalStateTransfer(REST)isanarchitecturalstyle.ItwasdefinedbyRoyFieldinginhisdoctoraldissertation.RESThappensovertheHTTP1.1protocolusingHTTPverbs,suchasGET,POST,DELETE,PUT,andUniformResourceIdentifier(URI),forinstance,/users/profile/1orsales/cart/add/2.

TheRESTarchitecturehasthefollowingproperties:

Simplicity:PrettymuchalllanguageshavelibrariestomanipulateHTTPURIs.Interoperability:RESTislanguage,platform,andOSagnostic.ScalableandReliable:AsRESTisbasedonHTTP,youcanusetheHTTPservertoscaleupyourapplicationinconjunctionwithHTTPloadbalancer,theHTTPcaches,andHTTPDNS.SeparationofConcerns(SOC):AsyouhaveaURI,that'syourcontract,notthecode,underlyingbackend,ordatabase.Thismeansthatyoucanchangethedatabaseorlanguagewithoutaffectingthecode.Client/Server:ThereisaserverthatprovidestheRESTinterfaceandtheclients,whichcalltheRESTendpoints.

WebservicesthatembracetheRESTprinciplesareoftencalledRESTful.

RESTAPIdesignWhenyouareworkingwithREST,therearesomeprinciplesthatyoushouldkeepinmind,andtheseprinciplesshouldprovideguidanceforyourdesignchoiceswhenyouaredoingAPIdesign.

HTTPverbsdesignThesearethefollowingverbsfoundinHTTP:

GET:ThisisoftenusedtoanswerqueriesPUT:ThisisoftenusedtoinsertdataPOST:ThisisoftenusedtoupdatedataDELETE:Thisisoftenusedtoremovedata

Whydowekeepsayingoften?Well,therearesomeexceptionsinregardsofsizelimitations.Forinstance,fortheGETverb,wecan'thavearequestbiggerthan8192bytesor8KB.Ifyouneedtosendabiggerpayload,wewillneedtousethePOSTverb.

UniformAPIRESTusesauniformAPI.Forexample,considerthefollowingpieceofcode:

GET/users/1=Listinformationaboutuserid1

PUT/users/1=Insertuser1

POST/users/1=Updateuser1

DELETE/users/1=Deleteuser1

GET/users/=ListsAllusers

Ifwechangetheresourcefromuserstosales,theAPIwouldalmostbethesame.RetrievingdataisdoneusingGETandupdateisdoneviaPOST,soit'sauniformAPI.

ResponsewithHTTPstatuscodesRESTrunstheerrorhandlerusingtheHTTP1.1statuscodes.Forinstance:

200->OK:ThisisoftenusedwiththeGETverb201->Created:ThisisoftenusedbythePUT/POSTverbs204->NoContent:ThisisoftenfortheDELETEverb400->InvalidRequest:ThisoftenmeansaninvalidrequestforthePOST/PUTverbs404->NotFound:ThisisoftenusedwiththeGETverb500->InternalServerError-UnexpectedServerError:Thisisoftenusedbyalltheverbs

RESTAPIpatternsTherearesomecommonspatternsforgoodandclearRESTAPIdesigns,asfollows:

Usenouns;donotuseverbs:Often,youcanusestandardURIs,suchas/cars/or/members/.Youshouldnotuse/getCars/orgetMembers/becauseyouareusingtheURIwithaverb,andtheverbalreadytellstheactions.GETmethodshouldnotchangestate:Ifyouwanttochangethestateoftheserver,youwillneedtouseverbssuchasPUT,POST,orDELETE.GETshouldnotchangethestateoftheserver,soitshouldalwaysbesafecallingGETasmanytimesasyouwant.Thisiscalledidempotent.Prefersub-resourcerelation:Let'ssaywehavearesourcecalled/users/,andauserhasprojects.It'salwaysagoodideatousesub-resources,suchas/users/1/projects/2,becausewehavearelationshipbetweenusersandprojects.UseHTTPheaders:HTTPheadersshouldbeusedforserialization,security,andallthekindsofmetadatayourapplicationneeds.TheHTTPHeadersareoftenusedforcontentnegotiation.Forinstance,youmightdothefollowing:

HTTPHEADERContent-Type=XML-GET/cars/1

HTTPHEADERContent-Type=JSON-GET/cars/1

TheURIisthesame;however,basedontheheadertype,itwillreturndatainXMLorJSONformat.Filter,SortingandPagination:Sometimes,yourdatamaybebig.It'salwaysagoodideatoprovidemechanismstosort,filter,andpaginateasfollows:

GET/projects/1/tasks?by=priority->Sorting

GET/projects/1/tasks?status=done->Filter

GET/projects/1/tasks?limit=30&offset=5->Pagination

APIversioningTherearetwowaystoperformAPIversioning.Firststrategyistoversionbytheendpointexplicitsuchas/v1/cars.Thesecondstrategyisbasedonmetadatasuchas/cars/,butthenyouwillpassanHTTPHEADERversionasv1.

Bothstrategieshaveprosandcons.Explicitversioningismoreclear,andyoucanalwayscreateanewversionanddon'tbreakyourconsumers.Headerstrategyismoreelegant;however,itcangettrickytomanage.

Someanti-patternstobeavoidedThereareseveraltrapsintheRESTAPIdesign,butthefollowingthingsneedtobeavoided:

GETverbforeverythingIgnoringHTTPheaderssuchasMIME-typesReturning200whenanerrorhappensReturning500foraninvalidparameteroramissingparameter

CreatingourAPIwithRESTandJSONAlright,nowisthetimetodesignaRESTAPIforyourPlayframeworkapplication.WewillcreateanAPItoexportalldatainthesystem.ThisAPIwillbeREADonly;however,youcanaddwriteoperationsifyoulike.

Lateroninthischapter,wewilladdsomebackpressuretolimittheAPIRESTrateforconsumersandcreateaScalaclientapplicationforourRESTAPI.So,firstofall,let'sgetstartedwiththePlayframework(server)first.

Wedon'tneedanyextralibraryinordertocreateaRESTAPIinourPlayframeworkapplication.Wewilljustneedanewcontrollerandnewroutes.Additionally,wewillleveragemostofthecodewemadeinthepreviouschapters.

RestApiContollerLet'screateanewcontrollerlocatedatReactiveWebStore/app/controllers.

RESTAPIFrontControllerimplementation

RestApiController.scalafileshouldlooksomethinglikethis:

packagecontrollers

@Singleton

classRestAPIController@Inject()

(valproductService:IProductService,

valreviewService:IReviewService,

valimageService:IImageService)extendsController{



deflistAllProducts=Action{

valfuture=productService.findAll()

valproducts=Awaits.get(5,future)

valjson=ProductsJson.toJson(products)

Ok(json)

}

deflistAllReviews=Action{

valfuture=reviewService.findAll()

valreviews=Awaits.get(5,future)

valjson=ReviewsJson.toJson(reviews)

Ok(json)

}

defprocessImages={

valfuture=imageService.findAll()

valimages=Awaits.get(5,future)

valjson=ImagesJson.toJson(images)

json

}

deflistAllImages=Action{

Ok(processImages)

}

}

Basically,wehavethreefunctionshere.Thesefunctionslistallproducts,images,andreviews.Asyoucanseeatthetopofthecontroller,weareinjectingthethreeservicesthatwehaveforproducts,images,andreviews.

Thecodeisprettymuchstraightforwardforallfunctions.First,wewillcalltheproperservice,andthenwewillwaitfortheresultwiththeawaitobject.Oncewehavethedata,wewillcallafunctiontoconvertthedatatoJSON.

Let'stakealookattheJSONhelpersobjectsthatweusedhere.

JSONmappingOurRESTcontrollerusedJSONhelperobjectstomapobjectstoJSON.First,wewillstartwiththeProductsJSONhelper.

ProductsJsonislocatedatReactiveWebStore/app/controllers/Product.scala:

objectProductsJson{

importplay.api.libs.json._

importplay.api.libs.json.Reads._

importplay.api.libs.functional.syntax._

implicitvalproductWrites:Writes[Product]=(

(JsPath\"id").write[Option[Long]]and

(JsPath\"name").write[String]and

(JsPath\"details").write[String]and

(JsPath\"price").write[BigDecimal]

)(unlift(Product.unapply))

implicitvalproductReads:Reads[Product]=(

(JsPath\"id").readNullable[Long]and

(JsPath\"name").read[String]and

(JsPath\"details").read[String]and

(JsPath\"price").read[BigDecimal]

)(Product.apply_)

deftoJson(products:Option[Seq[Product]])=Json.toJson(products)

}

Basically,therearethreeimportantconceptshere.First,wehaveproductsWrites,whichmapsfromJSONtomodel,andProductforwrites,whichisalsoknownasdeserialization.WehaveanothermappingforserializationcalledproductsReads,whichconvertsobjectstoJSON.

Asyoucansee,weneedtomapallfieldsexistinginourmodel,suchasID,name,details,andprice.Thismappingmustmatchpropertypesaswell.IDmappingusesreadNullablebecauseIDisoptional.

Finally,wehaveafunctiontoconvertfromJSONtoobject,calledtoJson,whichusesagenericPlayframeworklibrarycalledJSON.Let'smoveforthenexthelper--thereview.

ReviewsJsonislocatedatReactiveWebStore/app/controllers/Review.scalaandshouldlooksomethinglikethis:

objectReviewsJson{




implicitvalreviewWrites:Writes[Review]=(


(JsPath\"productId").write[Option[Long]]and

(JsPath\"author").write[String]and

(JsPath\"comment").write[String]

)(unlift(Review.unapply))

implicitvalreviewReads:Reads[Review]=(


(JsPath\"productId").readNullable[Long]and

(JsPath\"author").read[String]and

(JsPath\"comment").read[String]

)(Review.apply_)

deftoJson(reviews:Option[Seq[Review]])=Json.toJson(reviews)

}

Here,wehavethesameconceptsthatwesawearlierintheProductsJSONhelper.Wehaveamappingforreadsandwritesandafunctionwhichconvertsamodel.ReviewtoJSON.Let'smovetothelasthelper,theImageJson.

ImagesJsonislocatedatReactiveWebStore/app/controllers/Image.scala,whichshouldlooksomethinglikethis:

objectImagesJson{




implicitvalimagesWrites:Writes[Image]=(



(JsPath\"url").write[String]

)(unlift(Image.unapply))

implicitvalimagesReads:Reads[Image]=(



(JsPath\"url").read[String]

)(Image.apply_)

deftoJson(images:Option[Seq[Image]])=Json.toJson(images)

}

Justaswiththeothertwomappers,wehavereads,writes,mappings,andthetoJsonfunction.Wearedonewithmappers,sonowthenextstepistocreatethenewroutes.

ConfiguringnewroutesWeneedtoaddthefollowingthreenewroutesforourRESTAPI,whichislocatedatReactiveWebStore/conf/routes:

#

#RESTAPI

#

GET/REST/api/product/all

controllers.RestAPIController.listAllProducts

GET/REST/api/review/all

controllers.RestAPIController.listAllReviews

GET/REST/api/image/allcontrollers.RestAPIController.listAllImages

Asyoucansee,wemappedallthelistoperationswejustcreated.

TestingtheAPIusingthebrowserNowwecanrun$activatorrunandtestournewRESTAPIusingourwebbrowser.

Gotohttp://localhost:9000/REST/api/product/all;youshouldseesomethingsimilartothefollowingscreenshot:

Let'slookatthereviewAPI.

Gotohttp://localhost:9000/REST/api/review/all;youshouldseeresultssimilartothefollowingscreenshot:

Finally,let'scheckouttheimageofRESTAPI.

Gotohttp://localhost:9000/REST/api/image/all;youshouldseeresultssimilartothefollowingscreenshot:

OK.NowwewillcontinuetoworkwithREST.Wejustfinishedtheserver;however,itisimportanttocreateaRESTclienttoconsumetheseRESTAPIs.

CreatingaScalaclientFirst,youwillneedtocreateanewproject.Gotoyourfilesystemandcreateafoldercalledrest-client.Then,createanotherfolderinsiderest-clientcalledproject.Insideproject,youwillneedtoaddthefollowingtwofiles:

build.properties:ThiscontainsanSBTconfiguration,suchasversionPlugins.sbt:ThiscontainsanSBTpluginsconfiguration

Let'sstartwithbuild.properties:

sbt.version=0.13.11

Asyoucanseehere,weareconfiguringthisprojecttouseSBTversion0.13.11.Now,wecanmovetothepluginsfile.

Configuringplugins.sbtYourplugins.sbtfileshouldlooksomethinglikethis:

addSbtPlugin("com.typesafe.sbteclipse"%"sbteclipse-plugin"%

"2.5.0")

addSbtPlugin("com.github.mpeltonen"%"sbt-idea"%"1.6.0")

Here,weareaddingEclipseandIntelliJsupport.Forthisbook,weareusingEclipse,butfeelfreetouseanythingyoulike.

Outsideoftheprojectfolder,underrest-client,wewillneedtoconfigurethebuild.sbtfile.

Configuringbuild.sbtYourbuild.sbtfileshouldlooksomethinglikethis:

name:="rest-client"

version:="1.0"




resolvers+=JavaNet1Repository

resolvers+="OSSSonatype"at

"https://oss.sonatype.org/content/repositories/releases"

resolvers+="SonatypeOSSSnapshots"at

"https://oss.sonatype.org/content/repositories/snapshots"

resolvers+="SonatypeOSSSnapshots"at

"https://oss.sonatype.org/content/repositories/snapshots"

resolvers+="amateras-repo"at

"http://amateras.sourceforge.jp/mvn/"

libraryDependencies+="com.typesafe.play"%"play-ws_2.11"%

"2.5.6"

libraryDependencies+="org.scalatest"%"scalatest_2.11"%"2.2.6"

%Test

Sohere,weareusingScalaversion2.11.7,andwearedeclaringjusttwodependencies.Onedependencyisfortests,whichisscala-test,andtheotherdependencyisonthePlayframeworkwslibrary,whichwewillusetocallourRESTAPIs.

Let'salsocreatetwosourcefolders,asfollows:

src/main/scala:ThisistheScalasourcecodesrc/test/scala:ThisistheScalatestsourcecode

OK.Nowwecanrun$sbtcleancompileeclipseinordertodownloadthedependenciesfromthewebandcreatealltheEclipseprojectfilesthatweneed.

NowwecanimportthiscodeinEclipseandmoveon.

ScalaclientcodeFirstofall,wewillneedtocreateaFactorytoinstantiatetheWSPlayframeworklibrarytocallwebservices.Undertherest-client/src/main/scalalocation,let'screateapackagecalledclientandaddthefollowingcodeunderWSFactory.scala:

packageclient

objectWSFactory{


importakka.stream.ActorMaterializer

defws={

implicitvalsystem=ActorSystem()

implicitvalmaterializer=ActorMaterializer()

importcom.typesafe.config.ConfigFactory

importplay.api._

importplay.api.libs.ws._

importplay.api.libs.ws.ahc.{AhcWSClient,AhcWSClientConfig}

importplay.api.libs.ws.ahc.AhcConfigBuilder

importorg.asynchttpclient.AsyncHttpClientConfig

importjava.io.File

valconfiguration=Configuration.reference++

Configuration(ConfigFactory.parseString(

"""

|ws.followRedirects=true

""".stripMargin))

valparser=newWSConfigParser(configuration,

play.api.Environment.simple(

newFile("/tmp/"),null))

valconfig=newAhcWSClientConfig(wsClientConfig=

parser.parse())

valbuilder=newAhcConfigBuilder(config)

vallogging=new

AsyncHttpClientConfig.AdditionalChannelInitializer(){

overridedefinitChannel(channel:io.netty.channel.Channel):

Unit={

channel.pipeline.addFirst("log",new

io.netty.handler.logging.LoggingHandler("debug"))

}

}

valahcBuilder=builder.configure()

ahcBuilder.setHttpAdditionalChannelInitializer(logging)

valahcConfig=ahcBuilder.build()

newAhcWSClient(ahcConfig)

}

}

Theprecedingcodeisjusttechnical.ThesearethestepsneededtoinstantiatetheWSClientoutsidethePlayframework.IfthisclientwasawebapplicationusingthePlayframework,itwouldbewayeasieraswecanjustuseGoogleGuiceandinjectwhatweneed.

ThemainideayouneedtokeepinmindisthatyouneedtouseAkkaandActorSysteminordertousethisfeature.Asyoucansee,allthiscodeislockedinsideanobjectinasinglefunctioncalledws.

Wewillneedsomeutilityclasstoworkwithfutures.AsweusewslibrarytocallRESTAPIs,itreturnsFuture.So,let'screateanewpackagecalledutils:

YourAwaits.scalafileshouldlooklikesomethinglikethis:

packageutils




objectAwaits{

defget[T](sec:Int,f:Future[T]):T={

Await.result[T](f,secseconds)

}

}

Theprecedingcodeisprettysimple.WeusedtheAwaitobjectandthenusedagenericTinordertoconverttheresulttoagenericparameterizedtype.Byusingthisparameter,wewillalsoreceivehowmanysecondsweshouldwaitbeforethetimeout.

CreatingourRESTclientproxiesWewillnowmakeRESTcalls;however,wewillcreateaScalaAPI.So,thedeveloperswhouseourrest-clientwon'tneedtodealwithRESTandjustexecutetheScalacode.Thisisgoodformanyreasons,someofwhichareasfollows:

SOC:WestillhaveseparationofconcernsbetweenthePlayframeworkandtheclientapplicationIsolation:IftheRESTAPIchanges,wewillneedtodealwithitontheproxylayerAbstraction:TherestoftheclientcodejustusesScalaanddoesnotknowanythingaboutRESTorHTTPcalls

Thesetechniquesareverycommonnowadayswithmicroservices.Thesetechniquescanalsobeknownasdriversorthickclients.Rightnow,wewillneedtocreatethreeproxies,oneforeachresource,thatwehaveontheRESTAPI.Let'screateanewpackagecalledproxy.

YourProductProxy.scalafileshouldlooksomethinglikethis:

packageproxy

importclient.WSFactory

importutils.Awaits

caseclassProduct


varname:String,

vardetails:String,

varprice:BigDecimal){



details:"+details+",price:

"+price+"}"

}

}

objectProductsJson{




implicitvalproductWrites:Writes[Product]=(


(JsPath\"name").write[String]and

(JsPath\"details").write[String]and

(JsPath\"price").write[BigDecimal]

)(unlift(Product.unapply))

implicitvalproductReads:Reads[Product]=(


(JsPath\"name").read[String]and

(JsPath\"details").read[String]and

(JsPath\"price").read[BigDecimal]

)(Product.apply_)

deftoJson(products:Option[Seq[Product]])=Json.toJson(products)

}

objectProductProxy{



importProductsJson._

valurl="http://localhost:9000/REST/api/product/all"

implicitvalcontext=

play.api.libs.concurrent.Execution.Implicits.defaultContext

deflistAll():Option[List[Product]]={

valws=WSFactory.ws

valfutureResult:Future[Option[List[Product]]]=

ws.url(url).withHeaders("Accept"->

"application/json").get().map(

response=>

Json.parse(response.body).validate[List[Product]].asOpt

)

valproducts=Awaits.get(10,futureResult)

ws.close

products

}

}

Wehavethreebigconceptsinthiscode.Firstofall,wehaveacaseclassthatrepresentstheproduct.TheprecedingcodeisverysimilartothecodewehaveonthePlayframeworkapplication.However,ifyoupayattention,youwillseeitismuchcleanerbecausewedon'thaveanymetadataaroundpersistence.

Youmightthink,thisisduplicatedcode!Itis,anditis100%okay.Duplicatecodeisdecoupled.RememberthatwehaveaRESTinterfaceandalsoaproxybetweentherestoftheclientcode,sowehaveatleasttwolayersofindirectionthatwecandealwithchanges.Ifthesetwocodebasessharethesameclass,wewouldhavecouplingandlessspacetoaccommodatechanges.

Thesecondbigconcepthereismapping.WewillreceiveJSON,andwewillwanttoconvertJSONtoourcaseclass,sowewillhavesimilarmappingthatwedidinthePlayframeworkapplication.

Finally,wehavetheproxyimplementation.WewillinstantiatethePlayframeworkWSlibraryusingourfactoryandcallthewsfunction.Then,wewillusetheurlfunctionpassingtheRESTAPIURIforproductsanddefineaheaderinordertoacceptJSON.WearealsodoingthisusingtheHTTPverb,GET.TheresponseismappedwithJson.parsepassingresponse.body.Additionally,wewillcallthevalidatefunctiontomakesurethisJSONmatchesourcaseclass.Thisvalidationisimportantbecausethenwecanbesurethattheformatdidnotchange,andthateverythingworksfine.WSwillreturnthisasaFuture,sowewilluseourAwaitshelpertogettheresult.

Let'smovetothenextproxy,thereview.

YourReviewProxy.scalafileshouldlooksomethinglikethis:

packageproxy


importutils.Awaits

caseclassReview



varauthor:String,

varcomment:String)

{


"Review{id:"+id+",productId:"+productId.getOrElse(0)

+",author:"+author+

",comment:"+comment+"}"

}

}

objectReviewsJson{




implicitvalreviewWrites:Writes[Review]=(



(JsPath\"author").write[String]and

(JsPath\"comment").write[String]

)(unlift(Review.unapply))

implicitvalreviewReads:Reads[Review]=(



(JsPath\"author").read[String]and

(JsPath\"comment").read[String]

)(Review.apply_)

deftoJson(reviews:Option[Seq[Review]])=Json.toJson(reviews)

}

objectReviewProxy{



importReviewsJson._

valurl="http://localhost:9000/REST/api/review/all"

implicitvalcontext=


deflistAll():Option[List[Review]]={

valws=WSFactory.ws

valfutureResult:Future[Option[List[Review]]]=



response=>

Json.parse(response.body).validate[List[Review]].asOpt

)

valreviews=Awaits.get(10,futureResult)

ws.close

reviews

}

}

Here,wehavethesameprinciplesthatwehadontheproductproxy,butthistimeforreview.Asyoucansee,wewillcalladifferentURI.Now,let'smovetothelastproxy--theImageProxy.scalafile.

YourImageProxy.scalafileshouldlooksomethinglikethis:

packageproxy


importutils.Awaits

caseclassImage



varurl:String)

{


"Image{productId:"+productId.getOrElse(0)+",url:"+url

+"}"

}

}

objectImagesJson{




implicitvalimagesWrites:Writes[Image]=(



(JsPath\"url").write[String]

)(unlift(Image.unapply))

implicitvalimagesReads:Reads[Image]=(



(JsPath\"url").read[String]

)(Image.apply_)

deftoJson(images:Option[Seq[Image]])=Json.toJson(images)

}

objectImageProxy{



importImagesJson._

valurl="http://localhost:9000/REST/api/image/all"

implicitvalcontext=


deflistAll():Option[List[Image]]={

valws=WSFactory.ws

valfutureResult:Future[Option[List[Image]]]=



response=>

Json.parse(response.body).validate[List[Image]].asOpt

)

valimages=Awaits.get(10,futureResult)

ws.close

images

}

}

That'sit.Wehavethesameconceptsasproductandreview.Wehavefinishedallourproxies.Now,itistimetotestourproxyimplementation.Thebestwaytodothisisviatests,solet'screateScalatestsforthesethreeimplementations.

CreatingScalaTesttestsfortheproxiesUnderthe/src/test/scalasourcefolder,wewillneedtocreateapackagecalledproxy.test.

YourProductProxtTestSpec.scalashouldlooksomethinglikethis:

packageproxy.test

importorg.scalatest._

importproxy.ProductProxy

classProductProxtTestSpecextendsFlatSpecwithMatchers{

"AProductRestproxy"should"returnallproducts"in{

valproducts=ProductProxy.listAll().get

productsshouldNot(be(null))

productsshouldNot(be(empty))

}

}

Thetestisquitesimple;wewilljusthavetocallthelistAlloperationinourproductproxyandthenaddsomeassertionstomakesuretheresultisnotnull.Wewillalsoshowalltheproductsintheconsole.

Now,wewillneedtocreatetestsforthereviewproxy,whichwillbesimilartotheproduct.

YourReviewProxyTestSpec.scalafileshouldlooksomethinglikethis:

packageproxy.test


importproxy.ReviewProxy

classReviewProxyTestSpecextendsFlatSpecwithMatchers{

"AReviewRESTProxy"should"returnallreviews"in{

valreviews=ReviewProxy.listAll().get

reviewsshouldNot(be(null))

reviewsshouldNot(be(empty))

for(r<-reviews){

println(r)

}

}

}

Here,weusedtheproxyideastotestthereview.WecalledtheproxyusingthelistAllfunctiontogetallthereviews.Later,wewillchecktoseeifthereviewisnotnull.Wewillprintallthereviews.Finally,it'stimetomovetothelastproxytest--theimageproxy.

YourImageProxyTestSpec.scalashouldlooksomethinglikethis:

packageproxy.test


importproxy.ImageProxy


importplay.api.libs.concurrent.Execution.Implicits.defaultContext

importjava.util.concurrent.CountDownLatch

classImageProxyTestSpecextendsFlatSpecwithMatchers{

"AImageRESTProxy"should"returnallimages"in{

valimages=ImageProxy.listAll().get

imagesshouldNot(be(null))

imagesshouldNot(be(empty))

for(i<-images){

println(i)

}

}

}

Samedealgoesfortheimageproxy.Wehaveallourtests;now,wecanrunthetests.YouwillneedtomakesureourReactiveWebStorePlayframeworkappisupandrunning.

Let'srunthistestwithsbt:

openyourconsoleandtypein$sbttest

Alright,itallworks!Ournextstepwillbetoaddbackpressure.

AddingbackpressureBackpressureisawell-knownconceptintheautomotiveindustry.Nowadays,thistermisusedinsoftwareengineeringaswell.Backpressureintheautomotiveworldreferstothepressureopposedtothedesiredflowofgassesinaconfinedplace,suchasapipe.Forsoftwareengineering,itisoftenrelatedtoslowingdownaproducer,whichcanbeanapplication,astreamprocessingengine,oreventheuseritself.

WhenweareexecutingREST,it'seasytoreachasituationwheretheclientcansaturatetheserver.Thiscanbeasecuritybreachtoo,whichisalsoknownastheDenialOfService(DOS)attack.

Therearetwoarchitecturalscenarios.Inthefirstscenario,yourRESTAPIisinternal,andyoujusthaveconsumersinyourcompany.Inthesecondscenario,youaremakingtheRESTAPIapublicAPIsothatitwillbeopentothewholeInternet.Forthisscenario,youreallyshouldhavebackpressure,alsoknownasthrottling.

It'spossibletoscaleourarchitectureinordertohandlemoreusers.Wewilldiscussthis,andthescalabilitytechniques,inChapter10,ScalingUp.

Currently,thereareseveralwaystoapplybackpressure.Forinstance,ifourcodeispureRxScala/RxJava,wecanapplybackpressureonobservables.Moredetailscanbefoundathttps://github.com/ReactiveX/RxJava/wiki/Backpressure.

AsweareexposingaRESTinterface,wewilladdbackpressureonthecontroller,sowewillneedtocreateanewclasswiththebackpressurecode.

Therearesomealgorithmsforbackpressure;wewillusetheleakybucketalgorithm.Thealgorithmitselfisverysimple--just30linesofScalacode.

Theleakybucketalgorithm

Theleakybucketmetaphorisprettysimple.Let'stakealookatitinthefollowingdiagram:

https://github.com/ReactiveX/RxJava/wiki/Backpressure

Themetaphorbehindthealgorithmisbasedaroundabucketwithholes.Thewaterflowsordripsintothebucketandleaksthroughtheholesofthebucket.Ifthereistoomuchwater,andthebucketisfullofwater,thewaterwillspilloutofthebucket--inotherwords,itwillbediscarded.

Thisalgorithmisusedinnetworkprograming,andalsobythetelecommunicationindustry.TheAPImanagersolutionsarealsousecasesforthisalgorithm.

ThisconceptallowsRATElimitconstraints.Wecanexpressthebackpressureratelimitsinrequestspertime.Time,inthiscase,isoftenmeasuredinsecondsorminutes,sowehaveRequestsPerSecond(RPS)orRequestsPerMinute(RPM).

Youcanimplementthisalgorithmwithaqueue.However,inourimplementation,wewillnotuseaqueue;wewillusetimeinordertocontroltheflow.Ourimplementationwillalsobelockfree,ornon-blocking,aswewon'tusethreadsorexternalresources.

NowisthetimetocodealeakybucketinScala.Firstofall,wewillcreatethiscodefortheReactiveWebStoreapplication.WewillneedtocreateanewpackagelocatedatReactiveWebStore/app.Thenewpackagenamewillbebackpressure.

Scalaleakybucketimplementation

YourLeakyBucket.scalafileshouldhavethefollowingfiles:

packagebackpresurre


importjava.util.Date

classLeakyBucket(varrate:Int,varperDuration:FiniteDuration){

varnumDropsInBucket:Int=0

vartimeOfLastDropLeak:Date=null

varmsDropLeaks=perDuration.toMillis

defdropToBucket():Boolean={

synchronized{

varnow=newDate()

if(timeOfLastDropLeak!=null){

vardeltaT=now.getTime()-timeOfLastDropLeak.getTime()

varnumberToLeak:Long=deltaT/msDropLeaks

if(numberToLeak>0){

if(numDropsInBucket<=numberToLeak){

numDropsInBucket-=numberToLeak.toInt

}else{

numDropsInBucket=0

}

timeOfLastDropLeak=now

}

}else{

timeOfLastDropLeak=now

}

if(numDropsInBucket<rate){

numDropsInBucket=numDropsInBucket+1

returntrue;

}

returnfalse;

}

}

}

Asyoucanseehere,wecreatedaScalaclassthatreceivestwoparameters:rateandperDuration.Rateisaninteger,whichshowshowmanyrequestsweareabletohandlebeforeapplyingbackpressure.PerDurationisaScalaFiniteDuration,whichcanbeanymeasureoftime,suchasmilliseconds,seconds,minutes,orhours.

Thisalgorithmkeepstrackofthetimeforthelastdropinthebucket.Asyoucansee,thecodeissynchronized,butitisfinebecausewewon'tcalleitherexternalresourcesorthreads.

First,wewillgetthecurrenttimewithnewaDate().Thefirsttimewerunthealgorithm,wewillfailontheelsestatement,andwewillgetthecurrenttimeaslastleak.

Thesecondtimeitruns,itwillenteronthefirstIfstatement.Then,wewillcalculatethedelta(diff)betweenthelastleakandnow.ThisdeltawillbedividedbythetimeinmillisecondsthatyoupassedonperDuration.Ifthedeltaisgreaterthan0,thenweleak;otherwisewedrop.Then,wewillcapturethetimeagainforthelastleak.

Finally,wewillcheckthedroprate.Iftherateissmaller,wewillincrementandreturntrue,whichmeanstherequestcanproceed;otherwise,wewillreturnfalse,andtherequestshouldnotproceed.

NowthatwehavethisalgorithmcodedinScala,wecancallforoneofourcontrollers.WewilladdthisbackpressureontheimageRESTAPI.

YourRestApiController.scalashouldlooksomethinglikethis:

packagecontrollers





import


//RESToftheController...


varbucket=newLeakyBucket(5,60seconds)

defprocessImages={




json

}

defprocessFailure={

Json.toJson("TooManyRequests-TryAgainlater...")

}


bucket.dropToBucket()match{

casetrue=>Ok(processImages)

casefalse=>

InternalServerError(processFailure.toString())

}

}

}

Here,wewillcreatealeakybucketwithfiverequestsperminute.Wehavetwofunctions:OnetoprocessimagesthatwillcalltheserviceandconverttheobjectstoJSON,andtheothertoprocessfailures.TheprocessFailuremethodwilljustsendamessagesayingthattherearetoomanyrequests,andwecan'tacceptrequestsrightnow.

So,forthelistAllImagesfunction,wewilljustcallthebuckettryingtodropandusetheScalapatternmatcherinordertoprocesstheproperresponse.Iftheresponseistrue,wewillreturnJSONwitha200HTTPcode.Otherwise,wewillreturna500internalerroranddenythatrequest.Here,weimplementedaglobalRATElimiter;however,mostofthetime,peopleperformthisoperationperuser.Now,let'sopenthewebbrowserandtrymorethanfiverequestswithinaminute.Youshouldseesomethinglikethefollowingscreenshotathttp://localhost:9000/REST/api/images/all:

Alright,itworks!Ifyouwaitaminuteandmakerequestsagain,youwillseethattheflowgetsbacktonormal.Thenextstepistoaddanewclienttest,becauseweknowthatifwecallanimagetoomuchinourRESTAPI,wewillbethrottled.

Wewillneedtoaddonemoretestintherest-clientScalaproject.Forthat,wewillneedtochangetheImageProxyTestSpec.

Testingbackpressure

YourImageProxyTestSpec.scalashouldlooksomethinglikethis:

packageproxy.test

classImageProxyTestSpecextendsFlatSpecwithMatchers{

//RESTofthetests...

"AImageRESTProxy"should"sufferbackpressure"in{

vallatch=newCountDownLatch(10)

varerrorCount:Int=0

for(i<-1to10){

Future{

try{

valimages=ImageProxy.listAll().get

imagesshouldNot(be(null))

for(i<-images){

println(i)

}

}catch{

caset:Throwable=>errorCount+=1

}

latch.countDown()

}

}

while(latch.getCount>=1)

latch.await()

errorCountshouldbe>=5

}

}

So,forthistest,wewillcallImageProxytentimes.Weknowthatnotallrequestswillbeservedaswehavebackpressureontheserver.Here,wecancalltheproxywithatry...catchblockandhaveanerrorcounter.Eachtimeitfails,wecanincrementit.So,here,weareexpectedtofailatleastfivetimes.

WearecreatingthecodewithFeaturesbecausewewanttherequeststohappenatthesametime.WewillneedtouseCountDownLatchfunction,whichisaJavautilityclassthatletsuswaitforallFuturestofinishbeforemovingon.ThisisdonebythecountDownfunction.Everytimeweexecutecountdown,wedecrementtheinternalcounter.Asyoucansee,wecreatedtheCountDownLatchfunctionwithten.

Finally,wehaveawhileblocktowaitforuntilthecounterhaspendingFutures.Nowwewait.Onceit'salldone,wecanchecktheerrorcount;itshouldbeatleastfive.That'sit.Wehavetestedourbackpressuremechanismanditallworks!

Now,itistimetomovetothenextfeaturethatwewillimplementinourapplication:Swagger--wewilladdSwaggersupporttoourRESTAPI.

AddingSwaggersupportSwagger(http://swagger.io/)isasimpleJSONandUIrepresentationtoolforRESTAPIs.Itcangeneratecodeinseverallanguages.Italsocreatesaverynicedocumentation,whichisalsoarunnableSwaggercodethatallowsyoutocallRESTwebservicesfromthedocumentationitgenerates.WewillneedtomakesomechangesinourPlayframeworkapplicationinordertogetSwaggerupandrunningwiththePlayframework.

Firstofall,wewillneedtoaddtheSwaggerdependencytobuild.sbt:

//Restofbuildfile...


//Restofotherdeps...

"io.swagger"%%"swagger-play2"%"1.5.2-SNAPSHOT"

)

Asyoucansee,weareusingaSnapshotversion.WhyuseSnapshot?Rightnow,itisnotsupportedonastableversion.Inordertoresolvethisdependency,wewillneedtouseGitandcloneanotherproject.Youcangetmoredetailsathttps://github.com/CreditCardsCom/swagger-play.Basically,youwillneedtowriteacommandasfollows:

$gitclonehttps://github.com/CreditCardsCom/swagger-play.git

$cdswagger-play/

$sbtpublishLocal

Now,wewillneedtoenableSwaggeronReactiveWebStore/conf/application.conf.

Yourapplication.conffileshouldlooksomethinglikethis:

play.modules{

enabled+="play.modules.swagger.SwaggerModule"

}

Next,wecanchangeourcontrollerinordertoaddSwaggersupport.SwaggerhasannotationinordertomaptheRESToperations.

YourRestAPIController.scalafileshouldlooksomethinglikethis:

packagecontrollers

@Singleton

@Api(value="/REST/api",description="RESToperationson

Products,ImagesandReviews.")





import


@ApiOperation(

nickname="listAllProducts",

http://swagger.io/

https://github.com/CreditCardsCom/swagger-play

value="FindAllProducts",

notes="ReturnsallProducts",

response=classOf[models.Product],

httpMethod="GET"

)

@ApiResponses(Array(

newApiResponse(code=500,message="InternalServer

Error"),

newApiResponse(code=200,message="JSONresponsewith

data")

)

)

deflistAllProducts=Action{

valfuture=productService.findAll()

valproducts=Awaits.get(5,future)

valjson=ProductsJson.toJson(products)

Ok(json)

}

@ApiOperation(

nickname="listAllReviews",

value="FindAllReviews",

notes="ReturnsallReviews",

response=classOf[models.Review],

httpMethod="GET"

)


newApiResponse(code=500,message="InternalServerError"),


data")

)

)

deflistAllReviews=Action{

valfuture=reviewService.findAll()

valreviews=Awaits.get(5,future)

valjson=ReviewsJson.toJson(reviews)

Ok(json)

}


varbucket=newLeakyBucket(5,60seconds)

defprocessImages={




json

}

defprocessFailure={

Json.toJson("TooManyRequests-TryAgainlater...")

}

@ApiOperation(

nickname="listAllImages",

value="FindAllImages",

notes="ReturnsallImages-Thereisthrottlingof5

reqs/sec",

response=classOf[models.Image],

httpMethod="GET"

)


newApiResponse(code=500,message="InternalServerError"),


data")

)

)


bucket.dropToBucket()match{

casetrue=>Ok(processImages)

casefalse=>InternalServerError(processFailure.toString())

}

}

}

Herewehaveseveralannotations.Firstofall,[email protected],wewilldefinetherootpathoftheRESTAPI.Then,foreachRESTAPIoperation,wehavethe@[email protected]@ApiOperationdefinestheRESTAPIitselfwhereyoucandefinetheparametersandtheHTTPverb,andalsoputsomenotes(documentation).It'salsopossibletodescribetheresult;inourcase,itwillbeaJSONrepresentationofthemodels.

That'sit!WehavethecontrollermappedtoSwagger.ThenextstepistoaddarouteforSwagger.Thisneedstobedonebyaddinganewlineasshowninthefollowingpieceofcodewhich,islocatedatReactiveWebStore/conf/routes:

//RESToftheotherroutes..

GET/swagger.jsoncontrollers.ApiHelpController.getResources

SwaggerUISwaggerwillgenerateaJSONresponseforourRESTAPI.It'spossibletousetheSwaggerUI,whichisveryniceandgiveslotsoffacilitiestothedeveloper.TherearetwowayswecanworkwiththeSwaggerUI:WecanuseitasastandaloneorwecanembedtheSwaggerUIintoourPlayframeworkapplication.

ThestrategywewillpickhereisembeddingtheSwaggerUIinourapplication.IfyouhavemultipleRESTAPIswithmultiplePlayapplicationsormicroservices,itisagoodideatohavethestandaloneinstallationoftheswaggerUI.

Intheprevioussteps,weenabledSwaggerinourapplication.Openyourbrowserandtypehttp://localhost:9000/swagger.json.Youcanfollowtheinstructionsathttp://swagger.io/swagger-ui/.Insummary,youwillgetthefollowingoutput:

http://swagger.io/swagger-ui/

BuildandinstallSwaggerStandalone

Nowwewilldownload,build,andinstallSwaggerStandalone.Let'sgetstartedbywritingthefollowinglinesofcode:

$sudoapt-getupdate$sudoapt-getinstallnodej$sudoapt-getinstallnpm

$gitclonehttps://github.com/swagger-api/swagger-ui.git$cdswagger-ui/$

sudo-Enpminstall-g$sudo-Enpmrunbuild$npmrunserve$GOTO:

http://localhost:8080/

OnceyoustarttheSwaggerUI,youcangotothebrowser,whereyouwillseethefollowing

output:

Now,let'sembedtheSwaggerUIintoourPlayframeworkapplication.

Wewillneedtocopythecontentfrom/swagger-ui/dist/intoourPlayframeworkapplicationunderReactiveWebStore/public.Then,wewillcreateafoldercalledswaggerui.

WewillneedtoeditonefileinordertoputourswaggerJSONURI.OpenReactiveWebStore/public/swaggerui/index.htmlandchangethe40tothefollowingcodeline:

url="http://localhost:9000/swagger.json";

That'sit.NowwewillneedtocreatealinkfromourapplicationtoembedtheswaggerUI.So,let'schangeReactiveWebStore/app/views/index.scala.html.

Yourindex.scala.htmlfileshouldlooksomethinglikethis:

@(message:String)(implicitflash:Flash)

@main("WelcometoReactiveWebStore"){


<BR>

<divclass="span12">


<divclass="span6">

<ahref="/product"><imgheight="42"width="42"

src="@routes.Assets.at("images/product.png")">Manage

Products</a><BR>

<ahref="/review"><imgheight="42"width="42"

src="@routes.Assets.at("images/review.png")">Manage

Reviews</a><BR>

<ahref="/image"><imgheight="42"width="42"

src="@routes.Assets.at("images/image.png")">Manage

Images</a><BR>

</div>

<divclass="span6">

<ahref="/reports"><imgheight="42"width="42"

src="@routes.Assets.at("images/reports.png")">Reports</a>

<BR>

<ahref="/chat/index_socket"><imgheight="42"width="42"

src="@routes.Assets.at("images/chat.png")">ChatRoom</a>

<BR>

<ahref="/assets/swaggerui/index.html"><imgheight="42"

width="42"

src="@routes.Assets.at("images/swagger.png")">SwaggerREST

API</a><BR>

</div>

</div>

</div>

</div>}

NowwecanrunourPlayapplicationwith$activatorrun.

Openthebrowserandgotohttp://localhost:9000/.Youwillseethefollowingscreenshot:

NowwecanopentheSwaggerUIbyclickingontheSwaggerRESTAPIlinkorbyjustgoingtohttp://localhost:9000/assets/swaggerui/index.html.Itshouldlooksomethinglikethis:

Asyoucansee,theSwaggerUIisverynice.Youcanclickoneachoperationandseemoredetailsonhowtheywork,whichHTTPverbtheyuse,andwhattheURIis.ThereisaTryitout!button.Let'sclickontheTryitout!buttonforproducts,whichwouldlooksomethinglikethis:

Asyoucansee,wehaveourJSONresultandalsosomeCURLsamplesaswell.

SummaryInthischapter,youlearnedhowtodesignaRESTAPIandchangedyourPlayframeworkapplicationinordertohaveSwaggersupport.YoucreatedaScalaclientlibraryusingproxytechniques,aswellasScalatestsfortheAPIs.Additionally,youwereintroducedtobackpressureusingtheleakybucketalgorithm.

Inthenextchapter,whichwillbethefinalchapter,youwilllearnaboutsoftwarearchitectureandscalability/resiliencytechniques,suchasdiscoverability,loadbalancers,caches,AkkaCluster,andtheAmazonCloud.

Chapter10.ScalingupInthepreviouschapters,webuiltaScalaandPlayframeworkapplication.WeusedthemosteffectiveframeworksandtoolsaroundtheScalaecosystem,suchasPlayframeworkandAkka;andweusedtheReactiveandFunctionalProgrammingtechniquesusingFuturesandRxScala.Additionally,wecreatedreportswithJasperandChatwithWebSockets.Thisisthefinalchapter,andwewilllearnhowtodeployandscaleourapplication.


StandalonedeployArchitectureprinciplesReactivedriversanddiscoverabilityMid-Tierload-balancer,timeouts,Backpressure,andcachingScalingupmicroserviceswithanAkkaclusterScalinguptheinfrastructurewithDockerandAWScloud

StandalonedeployThroughoutthisbook,weusedtheActivatorandSBTbuildanddevelopmenttools.However,whenwetalkaboutproduction,wecan'truntheapplicationwithSBTorActivator;weneedtodoastandalonedeploy.

WhataboutstandardJavaServletcontainers,suchasTomcat?Tomcatisgreat;however,Playisgreater.Youwon'tgetbetterperformancebydeployingyourapponTomcat.ThestandaloneplayusesNetty,whichhassuperiornetworkstack.

TherearesomesmallchangesthatwewillneedtomakeinordertodeployourapplicationforJasperreports.Don'tworry;thesechangesareverysimpleandstraightforward.

ReportsfolderWeneedtomovethereportstemplate(JRXMLfiles)fromthesourcefoldertothepublicfolder.Whydoweneedtodothis?Becausewhenwegeneratethestandalonedeploy,theywon'tbeincludedintheapplicationjars.WhatisinsidethepublicfolderwillbepackedanddeployedintoaproperJARfile.That'swhyweneedtomakethischange.

CreateafoldercalledreportsatReactiveWebStore/public/.ThenmovealltheJRXMLfilesthere.

ChangingreportbuilderAsourtemplateswillbeinsideaJARfile,weneedtochangetheloadinglogicinordertogetthetemplatesproperly.UnderReactiveWebStore/app/report/,weneedtochangeReportBuilder.scala,whichshouldlooksomethinglikethisafterediting:

packagereports

objectReportBuilder{

privatevarreportCache:scala.collection.Map[String,Boolean]=

newscala.collection.mutable.HashMap[String,Boolean].empty

defgenerateCompileFileName(jrxml:String):String=

"/tmp/report_"+jrxml+"_.jasper"

defcompile(jrxml:String){

if(reportCache.get(jrxml).getOrElse(true)){

valdesign:JasperDesign=JRXmlLoader.load(

Play.resourceAsStream("/public/reports/"+jrxml)

(Play.current).get)

JasperCompileManager.compileReportToFile(design,

generateCompileFileName(jrxml))

reportCache+=(jrxml->false)

}

}

deftoPdf(jrxml:String):ByteArrayInputStream={

try{

valos:OutputStream=newByteArrayOutputStream()

valreportParams:java.util.Map[String,Object]=

newjava.util.HashMap()

valcon:Connection=

DriverManager.getConnection("jdbc:mysql://localhost/RWS_DB?

user=root&password=&useUnicode=

true&useJDBCCompliantTimezoneShift=

true&useLegacyDatetimeCode=false&serverTimezone=UTC")

compile(jrxml)

valjrprint:JasperPrint=

JasperFillManager.fillReport(generateCompileFileName(jrxml),

reportParams,con)

valexporter:JRPdfExporter=newJRPdfExporter()

exporter.setExporterInput(newSimpleExporterInput(jrprint));

exporter.setExporterOutput(

newSimpleOutputStreamExporterOutput(os));

exporter.exportReport()

newByteArrayInputStream

((os.asInstanceOf[ByteArrayOutputStream]).toByteArray())

}catch{

casee:Exception=>thrownewRuntimeException(e)

null

}

}

}

Themainchangesthatwemadewerearoundthecompilefunction.Now,weareusingtheJasperJRXmlLoaderinordertoloadtheJaspertemplatefromanInputStreammethod.PassingtheInputStreammethodprovidedbythePlay.resourceAsStreamfunction.Asyou

cansee,wearepassingthenewpath,/public/reports/,inordertogetthetemplates.Therestofthecodeisprettymuchthesameastheoneweexecutedearlier.

Nowwearereadytodeploy.Inordertodoso,wewillneedtorunacommandonactivator,whichisasfollows:

$activatoruniversal:packageZipTarball


Assoonasthetaskisfinished,ourappwillbepackedintotheReactiveWebStore/target/universal/directory,andyouwillseeareactivewebstore-1.0-SNAPSHOT.tgzfile.

Thenyouneedtoextractthefileandyoushallhavethefollowingdirectory:

reactivewebstore-1.0-SNAPSHOTbin:Scriptstoruntheappconf:Allconfigfiles:routes,logging,messagesbib:AllJARsincludingthird-partydependenciesshare:Alldocumentationabouttheapp

DefiningthesecretBeforewerunourstandaloneapplication,wewillneedtoapplyonemorechange.Weneedtochangethedefaultsecret.Locatethereactivewebstore-1.0-SNAPSHOT/conf/application.conffile.

Changethesecrettofollowingintheapplication.conffile:

play.crypto.secret="changeme"

Youwillneedtoprovideadifferentvalue.Itcanbeanything,aslongasyoudon'tcallitchangeme.Ifyoudon'tchangethis,yourapplicationwillnotbootup.Youcangetmoreinformationathttp://www.playframework.com/documentation/latest/ApplicationSecret.

Ifyoujustwanttotestthedeployfornow,let'scallitplayworks.

Now,weareallsettostarttheapplication.

http://www.playframework.com/documentation/latest/ApplicationSecret

RunningthestandalonedeployInordertoruntheapp,wewillusethescriptgeneratedbytheuniversaltask.Gotothereactivewebstore-1.0-SNAPSHOTdirectoryandthenrun$bin/reactivewebstore,whichwouldlooksomethinglikethis:

Now,youcanopenyourbrowserandgotohttp://localhost:9000/.

That'sit;wehaveourappupandrunning.Feelfreetotestallthefeatureswebuilt--theyallwork!

Itshouldlooksomethinglikethis:

ArchitectureprinciplesScalabilityisabouthandlingmoreusers,traffic,anddata;andinordertodoit,wewillneedtoapplysomeprinciplesandtechniques.Ourapplicationisalreadyusingthemostmoderntechniquesandtechnologies,suchasfunctionalandReactiveXprogramming,RxScala,Akkaframework,Play,andmuchmore.However,inordertoscale,wewillneedtohaveaninfrastructureinplaceandotherkindsofsystemthatwillallowustohandlemoreusers.

Agoodapplicationarchitectureshouldbecreatedaroundthefollowingprinciples:

SeparationofConcerns(SOC)(moredetailsathttps://en.wikipedia.org/wiki/Separation_of_concerns)ServiceOrientation(SOA/microservices)PerformanceScalability/Resiliency

Let'sseetheseprinciplesindetail.

https://en.wikipedia.org/wiki/Separation_of_concerns

Serviceorientation(SOA/microservices)Serviceorientationisabouthavingahigherlevelofabstraction,whichisalsocalledservicesormicroservices.SOAisnotaboutaspecifictechnology,butaboutprinciplessuchassharedservices,flexibility,andintrinsicoperability.IfyouwanttolearnmoreaboutSOA,checkouttheSOAManifestoathttp://www.soa-manifesto.org/.MicroservicesisaparticularflavorofSOAwherethemaindifferenceisthefocusonthegranularity,autonomy,andisolation.Ifyouwanttolearnmoreaboutmicroservices,youcancheckouthttps://www.linkedin.com/pulse/soa-microservices-isolation-evolution-diego-pachecoaswellashttp://microservices.io/.

http://www.soa-manifesto.org/

https://www.linkedin.com/pulse/soa-microservices-isolation-evolution-diego-pacheco

http://microservices.io/

PerformanceTherightalgorithmmightmakeyourapplicationworksmoothlyandthewrongalgorithmmightmakeyourusershaveapoorexperience.Performanceisachievedbydesign--firstofall,choosetherightsetofcollectionsandtherightsetofalgorithmsandframeworks.However,performanceneedstobemeasuredandtunedeventually.Thepracticeyoushoulddoinyourapplicationwithregardofperformanceisstresstesting.ThebeststresstestingtoolsintheScalaecosystemisGatling.Gatling(http://gatling.io/#/)allowsyoutocodeinScalausingaverysimpleyetpowerfulDSL.GatlingfocusesonHTTPandlatencypercentilesanddistributions,whichistherightthingtodonowadays.Latencyisnotonlyusedforthesakeofperformanceandscalability,butitisalsoheavilyrelatedtouserexperienceaseverythingisonline.

http://gatling.io/#/

Scalability/ResiliencyScalabilityisoneofthemainreasonswhywedosoftwarearchitecture,becauseanarchitecturethatdoesnotscaledoesnothavebusinessvalue.WewillcontinuetalkingaboutScalabilityprinciplesduringthischapter.Resiliencyisabouthowmuchthesystemcanresistandkeepoperatingunderthemostadversesituations,suchashardwarefailureorinfrastructurefailure.Resiliencyisanoldterm.Currently,thereisanewandmoremodernandaccurateprinciplecalledantifragility.ThisprinciplewaswelldevelopedandusedinpracticebyNetflix.Antifragilityisaboutsystemsandarchitecturethatcanadaptandfailovertoothersystemsandotheroperationalmodestokeepworkingnomatterwhat.Ifyouwanttoknowmoreaboutantifragility,youcanvisithttp://diego-pacheco.blogspot.com.br/2015/09/devops-is-about-anti-fragility-not-only.htmlandhttp://diego-pacheco.blogspot.com.br/2015/11/anti-fragility-requires-chaos.html.

http://diego-pacheco.blogspot.com.br/2015/09/devops-is-about-anti-fragility-not-only.html

http://diego-pacheco.blogspot.com.br/2015/11/anti-fragility-requires-chaos.html

ScalabilityprinciplesHavingarchitecturearoundtheseprinciplesmakesitpossibletoscaleyourapplicationup.However,wewillstillneedtorelyonotherprinciplesandtechniquestoscaleit.

Thereareseveralprinciplesandtechniquesforscalability,whichareasfollows:

Verticalandhorizontalscaling(upandout)CachingProxyLoadbalancerThrottlingDatabaseclusterCloudcomputing/containersAutoScalingReactivedrivers

Verticalandhorizontalscaling(upandout)Youcanaddmoreresources,havebetterhardware,oryoucanaddmoreboxes.Thesearethetwobasicwaystoscale.Youcanalwaysimproveandtuneyourapptousefewerresourcesandgetmorefromasinglebox.Recently,therewereseveralimprovementsinthisareaaroundreactiveprogrammingthatusesfewerresourcesanddeliversmorethroughput.However,therearealwayslimitstowhichasingleboxcanprovideinsenseofscalingup,whichiswhywealwaysneedtobeabletoscaleout.

CachingDatabasesaregreat.However,thereisalatencycosttocallatraditionaldatabase.Agreatwaytofixthisishavingamemorycache,whichyoucanuseasasubsetofyourdataandgetthebenefitoffastretrieval.Playframeworkhascachesupport.Ifyouwanttolearnmore,checkouthttps://www.playframework.com/documentation/2.5.x/ScalaCache.

Thereareotheroptionsinsenseofcaching.Therearelotsofcompaniesthatusethememoryasadefinitivedatastorenowadays.Forthis,youcanconsidertoolssuchasRedis(http://redis.io/)andMemcached(https://memcached.org/).However,ifyouwanttoscaleRedisandMemcached,youwillneedsomethinglikeNetflix/Dynomite(https://github.com/Netflix/dynomite).DynomiteprovidesaclusterbasedonAWSDynamopaperforRedis,whichhasthefollowingbenefits:

HighthroughputandlowlatencyMulti-regionsupport(AWScloud)TokenawareConsistenthashingReplicationShardingHighavailability

Note

Ifyouwanttolearnmoreaboutdynomite,checkouthttps://github.com/Netflix/dynomite/wiki.

https://www.playframework.com/documentation/2.5.x/ScalaCache

http://redis.io/

https://memcached.org/

https://github.com/Netflix/dynomite

https://github.com/Netflix/dynomite/wiki

LoadbalancerAloadbalancerisakeytooltoscaleservers.So,let'ssay,youhave10boxeswithourPlayframeworkapplicationor10Dockercontainers.Wewillneedsomethinginfrontofourapplicationtodistributethetraffic.Thereareseveralserversthatcandothis,suchasNGINX(https://nginx.org/)andApacheHTTPServer(https://httpd.apache.org/).Ifyouwanttoscaleyourapplication,thisistheeasiestsolutionforit.Configurationandmoredetailscanbefoundathttps://www.playframework.com/documentation/2.5.x/HTTPServer#Setting-up-a-front-end-HTTP-server.

Loadbalancersareoftenproxyserversaswell.YoucanusethemtohaveHTTPSsupport.Ifyouwant,youcanhaveHTTPSonPlayframeworkaswell(https://www.playframework.com/documentation/2.5.x/ConfiguringHttps).KeepinmindthatyouwillneedtochangeswaggerembeddedinstallationasallthecodethatwehavepointstotheHTTPinterface.IfyouaredoingdeploysintheAWScloud,youwillneedtochangesomeoftheconfigurationtoforwardtheproxies,whichyoucanfindathttps://www.playframework.com/documentation/2.5.x/HTTPServer#Setting-up-a-front-end-HTTP-server.

https://nginx.org/

https://httpd.apache.org/

https://www.playframework.com/documentation/2.5.x/HTTPServer#Setting-up-a-front-end-HTTP-server

https://www.playframework.com/documentation/2.5.x/ConfiguringHttps

https://www.playframework.com/documentation/2.5.x/HTTPServer#Setting-up-a-front-end-HTTP-server

ThrottlingThisisalsoknownasBackpressure.WecoveredthrottlinginChapter9,DesignYourRESTAPI.Youcangetmoredetailsthere.However,themainideaistolimittherequestforeachuser.Thisisalsoawaytomakesurethatasingleuserdoesnotstealallcomputationalresources.Thisisalsoimportantfromthesecuritypointofview,especiallyfortheservicesthatareInternet-facingoralsoknownasedge.AnothergreatwaytoprotectandhavethiscapabilityisusingNetflix/Zuul(https://github.com/Netflix/zuul).

https://github.com/Netflix/zuul

DatabaseclusterSometimes,theproblemisnotontheapplicationside,butinthedatabase.Whenwetalkaboutscalability,weneedbeabletoscaleeverything.WeneedtohavethesameconceptsfordatabasesthatwehavefortheMid-Tier.Fordatabases,itisimportanttoworkwiththefollowing:

ClusteringIndexMaterializedviewsDatapartition

Forourapplication,weusedtheMySQLdatabase.Herearesomeresourcesthatcanhelpyouscalethedatabaseandapplythepreviousconcepts:

http://dev.mysql.com/doc/refman/5.7/en/faqs-mysql-cluster.htmlhttp://www.fromdual.com/mysql-materialized-viewshttp://dev.mysql.com/doc/refman/5.7/en/optimization-indexes.htmlhttp://dev.mysql.com/doc/refman/5.7/en/partitioning.htmlhttps://dev.mysql.com/doc/refman/5.7/en/partitioning-overview.html

http://dev.mysql.com/doc/refman/5.7/en/faqs-mysql-cluster.html

http://www.fromdual.com/mysql-materialized-views

http://dev.mysql.com/doc/refman/5.7/en/optimization-indexes.html

http://dev.mysql.com/doc/refman/5.7/en/partitioning.html

https://dev.mysql.com/doc/refman/5.7/en/partitioning-overview.html

Cloudcomputing/containersScalingupapplicationintraditionaldatacentersisalwayshardbecauseweneedtohavethehardwareinplace.Thisgetsdonebythepracticeofcapacityplanning.Capacityplanningisgreattomakesurewedon'tspendmoneybeyondourbudget.However,itisveryhardtogetitdoneright.Softwareishardtopredict,andthat'sagreatadvantageofthecloud.Cloudisjustanotherlevelofabstraction.Hardwareandnetworksbecomelogical,andtheyareencapsulatedbehindAPIs.Thismakesiteasiertoscaleourapplicationaswecanrelyoncloudelasticityandscaleondemandwhenweneedto.However,thearchitectureneedstobereadyforthismomentandusethetoolsandtechniquesdescribedinthischapter.Currently,thereareseveralpublicclouds;thebestoptionsareasfollows:

AWS--AmazonCloud(https://aws.amazon.com/)GoogleCloud(https://cloud.google.com/)MicrosoftAzureCloud(https://azure.microsoft.com/en-us/)

Today,Cloudisnottheonlybigelephantintheroom.WealsohavetheLinuxcontainers,suchasDocker(https://www.docker.com/)andLXC(https://linuxcontainers.org/).Containersprovideanotherlevelofabstraction,andtheycanrunonthecloudoronpremises.Thismakesyourapplicationmoreportableandalsomorecosteffective.Containersalsoscale.Themainadvantagearoundcontainersisspeedandflexibility.It'swayfastertobootupacontainerincomparisonwithavirtualizedimageinanypubliccloud.Theyarealsoportableandcanruneverywhere.

https://aws.amazon.com/

https://cloud.google.com/

https://azure.microsoft.com/en-us/

https://www.docker.com/

https://linuxcontainers.org/

AutoScalingCurrently,thisisoneofthegreatestresourcesofcloudcomputing.Basically,youcandefineabaseimage,whichisastateofanoperationalsystemsuchasLinux,andthecloudwillcreateanddestroyinstancesforyouondemand.Theseinstancescanbecreatedbytheincreaseincomputationalresources,suchasmemory,CPU,network,orevenbasedoncustomrules.Thisisthekeyconcerninordertohaveelasticity.IfyouwanttolearnmoreaboutAutoScaling,checkouthttps://aws.amazon.com/autoscaling/.

https://aws.amazon.com/autoscaling/

AnoteaboutautomationInordertouseallthesetechniquesandtechnologiesatscale,weneedtohavefullautomation(https://en.wikipedia.org/wiki/List_of_build_automation_software)becauseitisimpossibletohandleallthiswithmanualwork.Whenweareusingthecloudorcontainers,thereisnootherwayaround;everythingneedstobeautomated.Thereareseveraltoolsthathelpusachievethisgoal,suchasAnsible(https://www.ansible.com/).

https://en.wikipedia.org/wiki/List_of_build_automation_software

https://www.ansible.com/

Don'tforgetabouttelemetryWhenyouhaveallinfrastructuresinplace,youwillalsoneedtohavemonitoring,alerting,andproperdashboards.Thereareplentyofgreattoolsforcontainersandpublicclouds,suchasSensu(https://sensuapp.org/)andPrometheus(https://prometheus.io/).

https://sensuapp.org/

https://prometheus.io/

ReactiveDriversanddiscoverabilityReactiveDrivers:WetalkedalotanddidalotofreactivecodeusingPlayframeworkandRxScala.However,tohavefullbenefitsofReactiveXprogramming,youneedtomakesureeverythingisanon-blockingIOandreactive.Inotherwords,weneedtohaveallofourdriversreactive.SlickisgreatbecauseitgivesusreactivitywiththeMySQLdatabase.Wewillneedtoapplythesameprincipleseverywherewehaveadriverorconnectionpoint.Therearelotsoflibrariesbecomingreactivethesedays.Forinstance,ifyouwanttocacheusingRedis,youcanuseLettuce(https://github.com/mp911de/lettuce),whichisreactive.

Whenweworkwithmicroservices,wetendtohavehundredsofmicroserviceinstances.Thesemicroserviceswillrunoncontainersand/orcloudcomputingunits.Youcan'tpointtospecificIPsbecausethecodewillnotbemanagedandwillnotsurviveinacloud/containerenvironment.Cloud/containerinfrastructureisephemeral,andyoudon'tknowwhenaninstancewillbeterminated.That'swhyyouneedtobeabletoswitchtoanotheravailabilityzoneorregionatanymoment.

Therearetoolsthatcanhelpusapplythesechangesinourcode.ThesetoolsareNetflix/Eureka(https://github.com/Netflix/eureka)andConsul(https://www.consul.io/),orevenApacheZookeeper(https://zookeeper.apache.org/).Eurekahasoneadvantage--itiseasiertouseandhastoolsaroundtheJVMecosystem,whichwasbattletestedbyNetflix.

EurekaisacentralregistrywheremicroservicesregistertheirIPandmetadata.EurekahasaRESTAPI.MicroservicescanusetheEurekaAPItoqueryandsearchexistingapplications.Eurekacanruninamulti-vpc/multi-regionenvironment.ThereareotherJVMcomponents,suchasribbon(https://github.com/Netflix/ribbon)andkaryon(https://github.com/Netflix/karyon),whichcanautomaticallyregisterandretrieveeurekainformationandmetadata.

BasedontheEurekainformation,youcanperformmicroserviceloadbalancingandfailovertootheravailabilityzonesandregionsautomatically.WhyuseEurekaifIcanuseDNS?DNSforMid-TierloadbalancingisnottherightchoiceasDNSisnotflexibleandthetimeoutisquitebig.Ifyouwantknowmoreaboutdiscoverability,checkouthttp://microservices.io/patterns/service-registry.html.

https://github.com/mp911de/lettuce

https://github.com/Netflix/eureka

https://www.consul.io/

https://zookeeper.apache.org/

https://github.com/Netflix/ribbon

https://github.com/Netflix/karyon

http://microservices.io/patterns/service-registry.html

Eurekaoverview-EurekaarchitectureoverviewontheAWScloud

Asyoucanseeintheprecedingdiagram,youwilldeploytheEurekaserveratleastinthreeAvailabilityZones(AZs)inordertohaveavailability.Then,Eurekadatawillbereplicatedtoeachserver.OurapplicationsormicroserviceswillregisterinEureka,andotherapplications/microservicescanretrievethismetadata,suchasIPaddress,tothemtotheRESTcalls.Ifyouwantlearnmore,youcancheckouthttps://github.com/Netflix/eureka/wiki/Eureka-at-a-glance.

https://github.com/Netflix/eureka/wiki/Eureka-at-a-glance

Mid-Tierloadbalancer,timeouts,Backpressure,andcachingEureka,Zookeeper,orConsulareonlyonepartoftheequation.WestillneedsomesoftwareontheclientsidethatcanusetheEurekainformationinordertodoMid-Tierloadbalancing,failover,andcaching.TheNetflixstackhasacomponentforthat,whichiscalledribbon(https://github.com/Netflix/ribbon).Withribbon,youcanautomaticallyresolvethemicroserviceIPsfromEureka,doretries,andfailovertootherAZsandregions.Ribbonhasacacheconcept;however,itisonpreloadedcache.

Ribbonideasaresimple.Thegreatthingaboutribbonisthateverythingisreactive,andyoucanuseRxJavaandRxScalainordertoworkwiththestack.Ifyoudon'twanttouseribbon,youcanstillcreateasimpleintegrationlayerwithScalaandperformthesameconcerns,suchasloadbalancing,failover,andcaching.

WhataboutBackpressure?BackpressurecanbedonewithRxJavaandRxscala,andyouwillbeabletodoitontheclientsideaswell.YoucanlearnmoreaboutBackpressureinRxathttps://github.com/ReactiveX/RxJava/wiki/Backpressure.

So,ifIhaveclient-sideloadbalancing,failover,caching,andBackpressure,amIgoodtogo?Yes,youare;however,wecanalwaysdobetter.Workingwithmicroservicesisnoteasyaseverythingisaremotecall,andremotecallscanfail,hang,ortimeout.Theseconsarehardanddangerousifnotmanagedwell.Thereisanothersolutionthatcanhelpusalotwiththisconcept;itiscalledHystrix(https://github.com/Netflix/Hystrix).

HystrixisalibraryfortheJVMdesignedforlatencyandfaulttoleranceprotection.Ataglance,Hystrixisawrapperaroundanyremotecodethatcantaketimeorgowrong.

Hystrixhasthreadisolationandprovidesadedicatedthreadpoolforeachresource.Thisisgreatbecauseitpreventsyoufromrunningoutofresources.Ithasanexecutionpatterncalledcircuitbreaker.Circuitbreakerwillpreventrequestsfromtearingdownthewholesystem.Additionally,ithasadashboardwherewecanvisualizethecircuits,so,atruntime,wecanseewhat'sgoingon.Thiscapabilityisgreatnotonlyforsenseoftelemetry,butalsobecauseitiseasytotroubleshootandvisualizewheretheproblemis.

Itcanbefurtherexplainedwiththehelpofthefollowingflowchart:

https://github.com/Netflix/ribbon

https://github.com/ReactiveX/RxJava/wiki/Backpressure

https://github.com/Netflix/Hystrix

ThecodeyouwanttoprotectwillbearoundaHystrixcommand.Thiscommandcanbemanipulatedinsyncorasyncprogrammingmodels.ThefirstthingthatHystrixwillcheckisifthecircuitisclosed,whichisgood,andhowitshouldbe.Then,itchecksiftherearethreadsavailableforthatcommand,andifthereareavailablethreads,thenthecommandwillbeexecuted.Ifthisfails,ittriestogetafallbackcode,whichisasecondoptionthatyoucanprovideincaseoffailure.Thisfallbackshouldbestatic;however,youcanbeloadingdatainthebackgroundandthenreturnonthefallback.AnotheroptionisfallbacktootherAZorRegion.

FollowingisasnapshotofhowaHystrixdashboardcircuitbreakerviewwouldwork:

Intheprecedingimage,wecanseetheHystrixdashboardsample,wherewecanvisualizecriticalinformation,suchassuccessanderrorrateandifthecircuitisopenorclosed.IfyouwantlearnmoreabouttheHystrixdashboard,checkouthttps://github.com/Netflix/Hystrix/wiki/Dashboard.

https://github.com/Netflix/Hystrix/wiki/Dashboard

ScalingupmicroserviceswithanAkkaclusterOurapplicationalsousesAkka.InordertoscaleAkka,wewillneedtouseanAkkacluster.TheAkkaclusterallowsustoclusterizeseveralActorsystemsinseveralmachines.IthasspecialActorroutersthatareclusteraware,andwecanusetheseActorstorouterequeststothewholecluster;moredetailscanbefoundathttp://doc.akka.io/docs/akka/2.4.9/java/cluster-usage.html#Cluster_Aware_Routers.

TheAkkaclusterprovidesmembershipprotocolandlifecycle.Basically,wecanbenotifiedbytheclusterwhenanewmemberjoinsorwhenamemberleavesthecluster.Giventhiscapability,itispossibleforustocodeascalablesolutionaroundthesesemantics.Asweknowwhenamemberjoins,wecandeploymorenodes,andwecanalsodropnodesondemand.

AsimplesamplewouldbetocreateanActorcalledfrontend,andwhenweseethisActor,wecoulddeploythreebackendActorsacrossthecluster.IfthefrontendActorleaves,wecouldundeploytheotherActors.AllthislogiccanbearchivedusingthemembershipprotocolandclusterseventsthatAkkageneratesforus.AfrontendActorisanotaUIorwebapplication,itisjustanActorthatreceiveswork.So,let'ssaywewanttogenerateanalyticsaroundourproductscatalog.WecouldhaveafrontendActorwhoreceivesthatrequestanddelegatestheworktobackendActors,whichwillbedeployedacrosstheclusteranddelivertheanalyticalwork.

ThefollowingimageistheprocessviewofanAkkaclustermembershipprotocol:

Asyoucanseeintheprecedingimage,thereisasetofstates.Firstofall,thenodeisjoining

http://doc.akka.io/docs/akka/2.4.9/java/cluster-usage.html#Cluster_Aware_Routers

thecluster;thenthenodecanbeup.Oncethenodeisup,itcanleavethecluster.Thereareintermediatestates,suchasleavingandexisting.

TheAkkaclusterprovidesmanyoptionstoscaleourActorsystem.AnotherinterestingoptionistousethepatternofdistributedPub/Sub.IfyouarefamiliarwithJMSTopics,itisalmostthesameidea.Forthosewhoarenotfamiliar,youcancheckouthttp://doc.akka.io/docs/akka/2.4.9/java/distributed-pub-sub.html.

Note

IfyouwantlearnmoreabouttheAkkacluster,youcancheckouthttp://doc.akka.io/docs/akka/2.4.9/common/cluster.html.

http://doc.akka.io/docs/akka/2.4.9/java/distributed-pub-sub.html

http://doc.akka.io/docs/akka/2.4.9/common/cluster.html

ScalinguptheinfrastructurewithDockerandAWScloudScalingupwiththeAWScloudiseasy,asatanymoment,withasimpleclickontheAWSconsole,youcanchangethehardwareandusemorememory,CPU,orbetternetwork.Scale-outisnothard;however,weneedtohavegoodautomationinplace.ThekeyprincipletoscaleistohavetheAutoScalinggroupsinplacewithgoodpolicies.Youcanlearnmoreaboutitathttp://docs.aws.amazon.com/autoscaling/latest/userguide/policy_creating.html.

Thereareotherinterestingservicesandcomponentsthatcanhelpyouscaleyourapplication.However,youwillneedtokeepinmindthatthiscanleadtocoupling.TheITindustryismovingtowardthecontainerdirectionbecauseitisfaster,andit'seasytodeployinotherpublicclouds.

WecanscaleoutwithDockeraswell,becausethereareclustermanagersthatcanhelpusscaleourcontainers.Currently,thereareseveralsolutions.Inthesenseofcapabilitiesandmaturity,thefollowingarethebettersolutions:

DockerSwarm(https://docs.docker.com/swarm/overview/)Kubernetes(http://kubernetes.io/)ApacheMesos(http://mesos.apache.org/)

DockerSwarm:ThisisaclusterforDocker.DockerSwarmisveryflexibleandintegrateswellwithotherDockerecosystemtools,suchasDockermachine,Dockercompose,andConsul.Itcanhandlehundredsofnodes,andyoucanlearnmoreaboutthemathttps://blog.docker.com/2015/11/scale-testing-docker-swarm-30000-containers/.

Kubernetes:ThiswascreatedbyGoogle,anditisafullsolutionfordevelopmentautomation,operation,andscalingDockercontainers.TheKubernetesclusterhastworoles,amasternodethatcoordinatesthecluster,schedulesapplications,andkeepsapplicationsonadesiredstate;andtherearenodes,thatareworkersthatrunapplications.Itcanhandlehundredsofcontainersandscaleverywell.Tolearnmoreaboutit,checkouthttp://blog.kubernetes.io/2016/03/1000-nodes-and-beyond-updates-to-Kubernetes-performance-and-scalability-in-12.html.

ApacheMesos:ThiswascreatedbyTwitter.Itisveryinteresting,asyoucanrunabaremetalonapremisesdatacenteroronapubliccloud.MesosallowsyoutouseDockercontainersaswell.Ifyouwanttolearnmoreaboutmesos,checkoutthefollowingpaper:

http://mesos.berkeley.edu/mesos_tech_report.pdf

http://docs.aws.amazon.com/autoscaling/latest/userguide/policy_creating.html

https://docs.docker.com/swarm/overview/

http://kubernetes.io/

http://mesos.apache.org/

https://blog.docker.com/2015/11/scale-testing-docker-swarm-30000-containers/

http://blog.kubernetes.io/2016/03/1000-nodes-and-beyond-updates-to-Kubernetes-performance-and-scalability-in-12.html

http://mesos.berkeley.edu/mesos_tech_report.pdf

SummaryInthischapter,youlearnedhowtodeployyourPlayframeworkapplicationasastandalonedistribution.Additionally,youlearnedseveralarchitecturalprinciples,techniques,andtools,tohelpyouscaleoutyourapplicationtothousandsofusers.

Withthis,wealsoreachtheendofthisbook.Ihopeyouenjoyedthisjourney.WebuiltaniceapplicationusingScala,PlayFramework,Slick,REST,Akka,Jasper,andRxScala.Thankyouforyourtime.IwishyouthebestinyourcodingcareerwiththeScalalanguage.

Documents

Building Applications with Scala - Sergey Drozdov. Sausage ...sd.blackball.lv/library/Building_Applications_with_Scala_(2016).pdf · Building Applications with Scala Credits About