Spring Web Flow:A little flow of happiness.

Сергей Моренец17 января 2013 г.

Agenda

• Overview of the navigation history• Basics of SWF• Practical usage• Pros & Contras• Q & A

Spring MVC

Navigation overview

JSP<jsp:forward page="/page.jsp" />

<%response.sendRedirect(“page.jsp");%>

<form action="search.jsp" name="search" method=“post"><input type="text" name="search" value="by keyword"><input type="submit" value="Go"></form>

Spring MVCController @RequestMapping("/secure") public class NavigationController {

@RequestMapping("/operation") public String processOperationPage() { return “/corpus/operation"; } }

<a href="secure/operation.htm">Operation</a>

Strutsstruts-config.xml

<action-mappings> <action path="/registration" type="net.sf.struts.flow.FlowAction" className="net.sf.struts.flow.FlowMapping">

<forward name="name" path="/name.jsp"/> <forward name="hobbies" path="/hobbies.jsp"/> <forward name="summary" path="/summary.jsp"/> </action></action-mappings>

JSFfaces-config.xml

<navigation-rule> <from-view-id>page1.xhtml </from-view-id> <navigation-case> <from-outcome>page2</from-outcome> <to-view-id>/page2.xhtml</to-view-id> </navigation-case> </navigation-rule>

<h:commandButton action="page2" value=“Next" />

Disadvantages• Visualizing the flow is very difficult• Mixed navigation and view• Overall navigation rules complexity• All-in-one navigation storage• Lack of state control/navigation customization

What is Spring Web Flow?

• Developed by Erwin Vervaet in 2004• Initial version released in October, 2006• Spring MVC extension• Introduces flows concept• Extends application scopes• SWF 2.3.1 released in April, 2012

Erwin Vervaet• Belgium citizen• Holds master's degree in computer science• Originator of Spring Web Flow Project• Senior project manager together with Keith

Donald• Speaker on the most Java and Spring related

themes• Independent consultant www.ervacon.com

What is SWF for?• How do you express page navigation rules?• How do you manage navigation and conversational

state?• How do you facilitate modularization and reuse?

Use case

Request diagram

Flow definition• XML document with predefined elements• Flow definition is composed of a set of states• Each state has one or more transitions that are used

to move to another state• A transition is triggered by an event

Sample flow<flow xmlns="http://www.springframework.org/schema/webflow"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://www.springframework.org/schema/webflowhttp://www.springframework.org/schema/webflow/spring-webflow-2.0.xsd">

[variables]

[input parameters]

[states]

</flow>

Flow• A flow defines a conversion, or dialogue, between

users and server that meets business goal

State• Action state• View state• Subflow state• Decision state• End state

Action state<action-state id="moreAnswersNeeded"> <evaluate expression="interview.moreAnswersNeeded()" /> <transition on="yes" to="answerQuestions" /> <transition on="no" to="finish" /></action-state>

public boolean moreAnswersNeeded() { return currentAnswer < answers.size();}

View state<view-state id="answerQuestions" > <on-entry> <evaluate expression="interview.getNextQuestionSet()" result="viewScope” </on-entry> <transition on="submitAnswers" to="moreAnswersNeeded"> <evaluate expression="interview.recordAnswers(questionSet)" /> </transition></view-state>

Decision state<decision-state id="moreAnswersNeeded"> <if test="interview.moreAnswersNeeded()" then="answerQuestions" else="finish" /></decision-state>

public boolean moreAnswersNeeded() { return currentAnswer < answers.size();}

Subflow state<subflow-state id=“registerUser" subflow=“register"> <transition on=“userCreated" to=“finish"> <evaluate expression=“interview.addUser( currentEvent.attributes.user)“</transition></subfow-state>

End state

<end-state id="finish" />

Start/end activity<on-start> <evaluate expression=“mainService.startLock(currentUser)" /></on-start>

<on-end> <evaluate expression=“mainService.releaseLock(currentUser)" /></on-end>

Transition binding

JSF<h:form>

<h:commandButton action="save" value="#{msg['buttons.save']}" />

<h:commandButton action="cancel" value="#{msg['buttons.cancel']}"

immediate="true" /></h:form>

Spring MVC<form:form> <button type="submit" id=“save" name="_eventId_save"> <spring:message code=“buttons.save"/> </button> <button type="submit" id="cancel" name="_eventId_cancel"> <spring:message code="buttons.cancel"/> </button></form:form>

Post redirect get(PRG)

Variables scope

Spring• Singleton• Prototype• Request• Session• Global-session

SWF scope• Request• Flash• View• Flow• Conversation

Request scope• Tied at the level of a single request• Not linked to a flow execution by itself

Flash scope• Extended request scope for PRG case• Useful for rendering error/warning messages

View scope• Can be referenced only within view state• Useful for storing data required with given view

only

Flow scope• Lives within flow session• Not available inside sub-flows

Conversation scope• Lives within entire flow execution• Available to all sub-flows

Flow scope usage<var name="items" class="java.util.ArrayList" />

<action-state id="init"> <on-entry> <evaluate expression="mainService.lookupItems(items)" /> </on-entry> <evaluate expression="items.size()" result="flowScope.size" /><transition on="success" to="viewitems" /></action-state>

View scope usage<view-state id="viewitems"> <var name="items" class="java.util.ArrayList" /> <on-entry> <evaluate expression="mainService.lookupItems(items)" /> <evaluate expression="items.size()“ result ="viewScope.size" /> </on-entry></view-state>

Presentation level <c:forEach items="#{items}“ var=“item"> <h:outputText value="#{item.text}" /></c:forEach>

<h:outputText value="#{size}" />

Flow trackingOriginal link http://mysite/site/main?id=1

Target http://mysite.com/site/main?execution=e2s1

Flow trackingpublic class PersistentUrlFlowHandler extends DefaultFlowUrlHandler {

public String createFlowExecutionUrl(String flowId,String flowExecutionKey, HttpServletRequest

request) {String url = super.createFlowExecutionUrl(flowId,

flowExecutionKey, request);if (request.getParameter("id") != null) {

StringBuilder builder = new StringBuilder(url);builder.append("&");appendQueryParameter(builder, "id",

request.getParameter("id"));return builder.toString();

}return url;

}

Flow trackingOriginal link http://mysite/site/main?id=1

Target http://mysite.com/site/main?execution=e2s1&id=1

Exception handling• Transition on exception• Custom exception handler

Transition on exception

<view-state id="authenticate" view="login" > <transition on="previous" to="previous"/> <transition on-exception="com.bookstore. AuthenticationException" to=“error_handler"/></view-state>

<action-state id=“error_handler”> ….</action-state>

Exception handler<exception-handler bean="exceptionHandlerBean" />

<bean id="exceptionHandlerBean" class="org.bookstore.exception. ExceptionHandlerBean"> <property name="errorUrl" value="/error“ /></bean>

Exception handlerpublic class WebflowExceptionHandlerBean implements FlowExecutionExceptionHandler {

private String errorUrl;

public boolean canHandle(FlowExecutionException ex) { return findServiceException(ex) != null; }

public void handle(FlowExecutionException ex, RequestControlContext context) {Exception flowException = findServiceException(ex);context.getExternalContext().requestExternalRedirect(errorUrl);

}

private Exception findServiceException(FlowExecutionException ex) {Throwable cause = ex.getCause();if (cause instanceof AuthenticationException) {return (Exception)cause;}return null;

}}

Flow inheritanceParent-flow

<flow … abstract="true"> <view-state id="someViewState" > <transition on="x" to="someState"/> </view-state></flow>

Child-flow<flow parent="parent-flow"> <view-state id="someViewState" > <transition on="y" to="someOtherState"/> </view-state></flow>

Integration• Spring MVC/Spring Security• JSF 2• Portlets• RichFaces/Apache MyFaces• Struts 2

Pros• High-level navigation control with clear

observable lifecycle• Designed to be self contained• Compile-independent• Easy to understand and visualize• Expression language support• Custom validation (including AJAX)• Integrates with major web frameworks

Cons• Requires Spring framework• Separate Spring project• Additional performance overhead• Lack of community support• Not suitable for simple or flow-free applications

Spring Tools Suite

• Eclipse development environment for building Spring-powered enterprise applications

• Visualization of Spring Web Flow

Flow graph

Flow editor

References• Spring Web Flow 2 Web Development. Markus

Stäuble, Sven Lüppken• Pro Spring MVC: With Web Flow. Marten Deinum,

Koen Serneels, Colin Yates, Seth Ladd, Christophe Vanfleteren

• Spring in Action.3rd edition .Craig Walls

Q&A

• Сергей Моренец, morenets@mail.ru