Spring Web Flow provides a framework for modeling complex navigation flows in web applications. It introduces the concept of flows, which define navigation through a series of states. States can include view states, action states, and decision states. Variables can be defined and shared across scopes like request, view, flow, and conversation. SWF integrates with Spring MVC and other frameworks and aims to simplify navigation management compared to alternatives.

1. Spring Web Flow:
A little flow of happiness.
Сергей Моренец
17 января 2013 г.

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

4. Spring MVC

5. Navigation overview

6. 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>

7. Spring MVC
Controller
@RequestMapping("/secure")
public class NavigationController {
@RequestMapping("/operation")
public String processOperationPage() {
return “/corpus/operation";
}
}
<a href="secure/operation.htm">Operation</a>

8. Struts
struts-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>

9. JSF
faces-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" />

10. 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

11. 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

12. 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

13. 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?

14. Use case

15. Request diagram

16. 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

17. 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/
webflow
http://www.springframework.org/schema/webflow/spring-
webflow-2.0.xsd">
[variables]
[input parameters]
[states]
</flow>

18. Flow
• A flow defines a conversion, or dialogue, between users
and server that meets business goal

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

20. 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();
}

21. 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>

22. Decision state
<decision-state id="moreAnswersNeeded">
<if test="interview.moreAnswersNeeded()"
then="answerQuestions" else="finish" />
</decision-state>
public boolean moreAnswersNeeded() {
return currentAnswer < answers.size();
}

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

24. End state
<end-state id="finish" />

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

26. Transition binding

27. JSF
<h:form>
<h:commandButton action="save"
value="#{msg['buttons.save']}" />
<h:commandButton action="cancel"
value="#{msg['buttons.cancel']}"
immediate="true" />
</h:form>

28. 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>

29. Post redirect get(PRG)

30. Variables scope

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

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

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

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

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

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

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

38. 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>

39. 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>

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

41. Flow tracking
Original link http://mysite/site/main?id=1
Target http://mysite.com/site/main?execution=e2s1

42. Flow tracking
public 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.getParamet
er("id"));
return builder.toString();
}
return url;
}

43. Flow tracking
Original link http://mysite/site/main?id=1
Target
http://mysite.com/site/main?execution=e2s1&id=1

44. Exception handling
• Transition on exception
• Custom exception handler

45. 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>

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

47. Exception handler
public 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;
}}

48. Flow inheritance
Parent-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>

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

50. 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

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

52. Spring Tools Suite
• Eclipse development environment for building
Spring-powered enterprise applications
• Visualization of Spring Web Flow

53. Flow graph

54. Flow editor

55. 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

56. Q&A
• Сергей Моренец, morenets@mail.ru