Java days Lviv 2015

#JavaEE#JavaEE @alextheedom@alextheedom

Professional Java EE Design PatternsAlex Theedom@alextheedom alextheedom.com

@alextheedom@alextheedom#JavaEE#JavaEE

Speaker’s BioSpeaker’s Bio

•Senior Java Developer

•Author: Professional Java EE Design Patterns

•E-learning Platforms

•Cash Machine Software

•Microservice Based Lottery Systems

•Spring and Java EE

What to expectWhat to expect

•What’s the story

•Why am I here? What’s the message?

•Whistle stop tour

•Design Patterns: what, when and why

•Context Dependency Injection

What to expectWhat to expect

•Deep Dive

•Singleton Pattern

•Factory Pattern

•Harnessing the power (something special)

•Quickie Patterns

•Façade, Decorator, Observer

•Q&A

What’s the storyWhat’s the story

•Java EE changed design pattern implementation

• Implementation has simplified

• Implementation has been enhanced

•Greater creativity

•How?

• I will show you today

•Change is part of Java EE continued development

Design patterns: 3W’SDesign patterns: 3W’S

•What are design patterns?

•Why do we need them?

•When to use them?

Context Dependency InjectionContext Dependency Injection

•Simplifies programming model

•Annotations have replaced XML config files

•Convention over Configuration

•Resources are injected by type

•@Inject and disambiguation @Qualifier

•POJO (JSR 299 managed bean)

•Otherwise @Producer

Singleton PatternSingleton Pattern

•Ubiquitous and controversial but inescapable

•Instantiated once

•Not normally destroy during application life cycle

Conventional ImplementationConventional Implementation

public class Logger { private static Logger instance; private Logger() { // Creation code here }

public static synchronized Logger getInstance() { if(instance == null) { instance = new Logger(); } return instance; } }

public class Logger { private static Logger instance; private Logger() { // Creation code here }

public static synchronized Logger getInstance() { if(instance == null) { instance = new Logger(); } return instance; } }

•Only one instance of Logger created

•Created by first call the getInstance()

•Thread safe creation

•Use it like so:

Logger logger = Logger.getInstance(); Logger logger = Logger.getInstance();

Java EE ImplementationJava EE Implementation @Singleton public class Logger {

private Logger() { // Creation code here }

@Singleton public class Logger {

Java EE ImplementationJava EE Implementation

•Only one instance of Logger created

•Created by container (lazily)

•Knows it’s a singleton because @Singleton

•Use it like so:

@Inject Logger logger; @Inject Logger logger;

•Eager instantiation @Startup

•Perform startup tasks @PostConstruct

@Startup @Singleton public class Logger {

@PostConstruct void startUpTask() { // Perform start up tasks } }

@Startup @Singleton public class Logger {

•Specify dependent instantiation

@DependsOn("PrimaryBean") @Startup @Singleton public class Logger { ... }

@DependsOn("PrimaryBean") @Startup @Singleton public class Logger {

•Conclusions so far

•Very different implementation

•Substantially less boilerplate code

•Enhancements via specialized annotations

•Further enhancements

•Fine grain concurrency management

•Container vs. bean managed

@Singleton @ConcurrencyManagement(ConcurrencyManagementType.BEAN) public class Logger { ... }

•What about method access?

•Method access

•LockType.WRITE and LockType.READ

@Lock(LockType.WRITE) public void addMessage(String message) { // Add message to log }

@Lock(LockType.READ) public String getMessage() { // Get message }

@Lock(LockType.WRITE) public void addMessage(String message) { // Add message to log }

@Lock(LockType.READ) public String getMessage() { // Get message }

•Method access timeout

•ConcurrentAccessTimeoutException

•Defined by annotation @AccessTimeout

•Class and method level

@AccessTimeout(value = 30, unit=TimeUnit.SECONDS) @Lock(LockType.WRITE) public void addMessage(String message) { // Add message to log }

ConclusionConclusion

•Substantially different manner of implementation

•Marked reduction in code (~50%)

•Implementation improved via specialized annotations

•Startup behavioural characteristics

•Fine grain control over concurrency and access timeout

Factory PatternFactory Pattern

•Creational pattern

•Interface for creating family of objects

•Clients are decoupled from the creation

public class DrinksMachineFactory implements AbstractDrinksMachineFactory{ public DrinksMachine createCoffeeMachine() { return new CoffeeMachine(); } }

•Use it like so:

AbstractDrinksMachineFactory factory = new DrinksMachineFactory(); DrinksMachine coffeeMachine = factory.createCoffeeMachine();

•Abstract factory

•CDI framework is a factory

public class CoffeeMachine implements DrinksMachine { // Implementation code }

•Use it like so:

@Inject DrinksMachine drinksMachine; @Inject DrinksMachine drinksMachine;

•Problem! Multiple concrete implementations

public class SoftDrinksMachine implements DrinksMachine { // Implementation code }

@Inject DrinksMachine drinksMachine; @Inject DrinksMachine drinksMachine;

•Which DrinksMachine to inject?

•Solution! Qualifiers

@Qualifier @Retention(RetentionPolicy.RUNTIME) @Target({ElementType.METHOD, ElementType.FIELD}) public @interface SoftDrink

@Qualifier @Retention(RetentionPolicy.RUNTIME) @Target({ElementType.METHOD, ElementType.FIELD}) public @interface Coffee

•Annotate respective classes

@Coffee public class CoffeeMachine implements DrinksMachine { // Implementation code }

@SoftDrink public class SoftDrinksMachine implements DrinksMachine { // Implementation code }

•Annotate injection points

@Inject @SoftDrink DrinksMachine softDrinksMachine; @Inject @SoftDrink DrinksMachine softDrinksMachine;

@Inject @Coffee DrinksMachine coffeeDrinksMachine; @Inject @Coffee DrinksMachine coffeeDrinksMachine;

•No boilerplate code

•Container does all the hard work

•Disambiguation via qualifiers

•Remember

•Only JSR299 beans are ‘injectable’

•Dive deeper

•Producer methods

•Use it like so:

@Produces @Library public List<Book> getLibrary(){ // Generate a List of books called 'library' return library; }

@Inject @Library List<Books> library; @Inject @Library List<Books> library;

•Scope

•Determines when method called

•Life of object: @RequestScoped -> @ApplicationScoped @SessionScoped @Produces @Library public List<Book> getLibrary(){ // Generate a List of books called 'library' return library; }

@SessionScoped @Produces @Library public List<Book> getLibrary(){ // Generate a List of books called 'library' return library; }

Java EE ImplementationJava EE Implementation•Parameterized creation

•Use it like so:

public class LoggerFactory{ @Produces public Logger logger(InjectionPoint injectionPoint) { return Logger.getLogger( injectionPoint.getMember() .getDeclaringClass().getName()); } }

@Inject private transient Logger logger; @Inject private transient Logger logger;

•Virtually any object can be made injectable

•Automatic per class configuration

Harnessing the power of CDIHarnessing the power of CDI

•A variation on the factory pattern

•Imaginative use of CDI

•Multiple implementations of the same interface

•Collect and select pattern

•Uses @Any, enums, annotation literals and Instance class

•@Any

@Any @Inject private Instance<MessageType> messages

•Distinguish between message types using qualifiers

@Qualifier @Retention(RetentionPolicy.RUNTIME) @Target({ElementType.FIELD, ElementType.TYPE}) public @interface Message { Type value(); enum Type{ SHORT, LONG } }

•Annotate our classes

@Message(Message.Type.SHORT) public class ShortMessage implements MessageType{ // Short message implementation code }

@Message(Message.Type.LONG) public class LongMessage implements MessageType{ // Long message implementation code }

•Create an annotation literal for messages

public class MessageLiteral extendsAnnotationLiteral<Message> implements Message {

private Type type; public MessageLiteral(Type type) { this.type = type; }

public Type value() { return type;

public class MessageLiteral extendsAnnotationLiteral<Message> implements Message {

private Type type; public MessageLiteral(Type type) { this.type = type; }

public Type value() { return type;

•Putting the puzzle together

@Inject @Any private Instance<MessageType> messages; public MessageType getMessage(Message.Type type) { MessageLiteral literal = new MessageLiteral(type); Instance<MessageType> typeMessages =

messages.select(literal); return typeMessages.get(); }

@Inject @Any private Instance<MessageType> messages; public MessageType getMessage(Message.Type type) { MessageLiteral literal = new MessageLiteral(type); Instance<MessageType> typeMessages =

messages.select(literal); return typeMessages.get(); }

•Use it like so:

@Inject private MessageFactory mf; public void doMessage(){ MessageType m = mf.getMessage(Message.Type.SHORT); }

ConclusionConclusion

•CDI removes need for factory pattern

•Container does all the hard work

•Substantially less boilerplate code

•Disambiguation via qualifiers

•Increased creativity

•Collect and select

Other PatternsOther Patterns

•Facade

•Decorator

•Observer

Façade PatternFaçade Pattern•Encapsulates complicated logic

•@Stateless, @Stateful

@Stateless public class BankServiceFacade{ @Inject private AccountService accountService;

@Stateless public class AccountService{} @Stateless public class AccountService{}

Decorator PatternDecorator Pattern

•Dynamically adds logic to an object

Decorator PatternDecorator Pattern

@Decorator @Priority(Interceptor.Priority.APPLICATION) public class PriceDiscountDecorator implements Product {

@Any @Inject @Delegate private Product product;

public String generateLabel() { product.setPrice(product.getPrice() * 0.5); return product.generateLabel(); } }

@Decorator @Priority(Interceptor.Priority.APPLICATION) public class PriceDiscountDecorator implements Product {

@Any @Inject @Delegate private Product product;

public String generateLabel() { product.setPrice(product.getPrice() * 0.5); return product.generateLabel(); } }

Observer PatternObserver Pattern

•Notifies dependents of state change

public void trace(@Observes String message){ // Response to String event }

Final ConclusionFinal Conclusion

•Efficiency savings

•Greater control over behaviour

•New features enhance implementation

•Opens doors to new pattern design

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@YourTwitterHandle#DVXFR14{session hashtag} @alextheedom@alextheedom#JavaEE#JavaEE

Professional Java EE Design PatternsAlex Theedom@alextheedom alextheedom.com

Thank You

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