Spring Web Flow. A little flow of happiness - Sergey Morenets, senior developer, Provectus IT

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