vb.net barcode Working with Phase Events and Listeners in Java

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Working with Phase Events and Listeners
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Recall that in addition to action events and value change events, the other common Faces event is known as the phase event Phase events are events that are processed in between each phase of the Faces request processing lifecycle Since they have the ability to execute in between the different phases, phase events and their respective phase listeners provide a unique way to jump into the execution of the lifecycle and check or alter values/properties of any object in a Faces application
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Using a PhaseListener to Observe the Faces Lifecycle in Action
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One of the most useful and simple things to do is to write a phase listener that executes at every phase in the Faces lifecycle and reports to either a logging facility (or even just to the console) when the different phases of the lifecycle are processed This type of phase listener
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Part I:
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The JavaServer Faces Framework
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is very easy to write and it can be used as a tool to confirm the correct execution of events and phases based on different criteria, such as when certain UI components have their immediate property set to true, or if a certain listener method short-circuits the lifecycle directly by calling the RenderResponse( ) method of the Faces context To build a phase listener to process the phase events that are emitted by the changing of lifecycle phases, simply create a Java class that implements the PhaseListener interface We begin by creating the following skeleton, called MyPhaseListener
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package comjsfcompref; import javaxfaceseventPhaseListener; public class MyPhaseListener implements PhaseListener { public MyPhaseListener() { } // Implement PhaseListener methods here }
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Next, the methods beforePhase( ), afterPhase( ), and getPhaseId( ) must be overridden and implemented Both the beforePhase( ) and afterPhase( ) methods accept a single argument of type PhaseEvent and execute either before or after the phase event is passed to the methods Each phase event has an associated phase ID and it can be used to pick when to execute the method Since the beforePhase( ) and afterPhase( ) methods execute for all phase events, if you want to a perform specific action for a single phase of the lifecycle, you can provide some simple logic to check the phase ID of the incoming phase event and then conditionally execute your code based on that check For example, the following beforePhase( ) method will print a message Processing new Request! to the console, but only when it processes a RESTORE_ VIEW phase event The subsequent statement will print a message before - phase id for all phase events of the lifecycle
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public void beforePhase(PhaseEvent pe) { if (pegetPhaseId() == PhaseIdRESTORE_VIEW) Systemoutprintln("Processing new Request!"); Systemoutprintln("before - " + pegetPhaseId()toString()); }
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A subsequent afterPhase( ) method can be similarly coded as:
public void afterPhase(PhaseEvent pe) { Systemoutprintln("after - " + pegetPhaseId()toString()); if (pegetPhaseId() == PhaseIdRENDER_RESPONSE) Systemoutprintln("Done with Request!\n"); } }
Notice how this method prints an after phase message for all phases It also prints a special Done with Request! when it encounters the final Render Response phase The final method to implement is getPhaseId( ), which is used to determine which phase this phase listener will process events for Since it must execute during every phase change, it returns ANY_PHASE
8:
The JSF Event Model
public PhaseId getPhaseId() { return PhaseIdANY_PHASE; }
PART I PART I PART I
The code to the phase listener is now complete, but to use it in the Faces application, its full classpath must be registered in the faces-configxml as follows:
<lifecycle> <phase-listener>comjsfcomprefMyPhaseListener</phase-listener> </lifecycle>
JSF 12 TIP In Faces 12 it is also possible to register phase listeners directly on the UIViewRoot
and avoid the necessity of including them in the faces-configxml file Once registered in a Faces application, the phase listener will report all of the lifecycle phases being entered during execution of the application For example, upon an initial, non-postback, request to a Faces application, the output in the console will look like this:
Processing new Request! before - RESTORE_VIEW 1 after - RESTORE_VIEW 1 before - RENDER_RESPONSE 6 after - RENDER_RESPONSE 6 Done with Request!
This confirms what was presented in 3 in that during an initial Faces request, where no data is being posted back to the application, the request processing lifecycle simply creates a new view of UI components (in the Restore View phase) and then renders a response to the client A subsequent request that now posts form information back to the application will cause the following output since the entire lifecycle will be processed
Processing new Request! before - RESTORE_VIEW 1 after - RESTORE_VIEW 1 before - APPLY_REQUEST_VALUES 2 after - APPLY_REQUEST_VALUES 2 before - PROCESS_VALIDATIONS 3 after - PROCESS_VALIDATIONS 3 before - UPDATE_MODEL_VALUES 4 after - UPDATE_MODEL_VALUES 4 before - INVOKE_APPLICATION 5 after - INVOKE_APPLICATION 5 before - RENDER_RESPONSE 6 after - RENDER_RESPONSE 6 Done with Request!
Once a phase listener like this has been installed, you can observe the effects of several changes that can affect the processing order of the Faces lifecycle For example, a page with a single commandButton that is bound to an action method, which prints out a message in action method, could have its immediate property set to true When the application is run, it will execute the action method at the end of the Apply Request Values phase as opposed to the Invoke Application phase where it would normally execute, as shown next
Part I:
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