Expert Spring MVC and Web Flow

Listing 12-16.org.springframework.webflow.execution.FlowExecutionListener

public interface FlowExecutionListener {

void requestSubmitted(RequestContext context);

void requestProcessed(RequestContext context);

void sessionStarting(RequestContext context, State startState, Map input)

throws EnterStateVetoException;

void sessionStarted(RequestContext context);

void eventSignaled(RequestContext context, State state);

void stateEntering(RequestContext context, State nextState)

throws EnterStateVetoException;

void stateEntered(RequestContext context, State previousState, State state);

void resumed(RequestContext context);

void paused(RequestContext context, ViewSelection selectedView);

void sessionEnding(RequestContext context);

void sessionEnded(RequestContext context, FlowSession endedSession);

}

Implementing a FlowExecutionListenerallows you to weave in behavior in an

interceptor-like way. For example, you could provide a SecurityFlowExecutionListener

implementation that throws an EnterStateVetoExceptionpreventing a state from entering

if the user does not have the necessary permissions. You might develop listeners to apply

custom auditing, breadcrumbs (navigation history), or transactional behavior and so on.

■Tip For convenience Spring Web Flow provides an empty FlowExecutionListenerimplementation,

org.springframework.webflow.execution.FlowExecutionListenerAdapter.

Listeners are attached to a FlowExecution via anorg.springframework.webflow.execution.

FlowExecutionListenerLoader.The FlowExecutionListenerLoaderinfrastructure allows you to

define which FlowExecutionListenersapply to which flow definitions. Spring Web Flow provides

an org.springframework.webflow.manager.ConditionalFlowExecutionListenerLoaderimplemen-

tation for convenience, which is registered with the FlowExecutionManagerimplementation.

Listing 12-17 shows how to amend the flowExecutionManagerdeclaration to attach a

collection of listeners to executions of all flow definitions.

Listing 12-17.XML Fragment to Register a Number of FlowExecutionListeners

<bean id="flowExecutionManager"➥

class="org.springframework.webflow.manager.FlowExecutionManagerImpl">

<constructor-arg ref="flowRegistry"/>

<property name="listenerLoader">

<bean

class="org.springframework.webflow.manager.ConditionalFlowExecutionListenerLoader">

<property name="listeners">

352 CHAPTER 12 ■ADVANCED SPRING WEB FLOW