JSF Under the Hood—Part 3 - JSF and HTML5 - page 93

Figure 4-2. JSF event listeners
There are two types of JSF event listeners:
• Faces Listener is the base interface for action listener, value change listener, System event
listener, and component System event listener.
• Phase Listener is the listener interface for the beginning and ending of each standard phase
of the JSF request processing lifecycle.
Let's go into the details of the child listeners to understand who can create these listeners and when they can be
executed. Figure 4-3 shows the two types of application-related event listeners:
• ActionListener interface, which is responsible for receiving action events.
• ValueChangeListener interface, which is responsible for receiving value change events.
Figure 4-3. Application-related event listeners
As shown in this figure, ActionSource component (or ActionSource2 component) may have more than one or
more action listener(s). EditableValueHolder component (such as UIInput component) or ValueHolder component
may have one or more value change listener(s).
System event listeners, by definition, listen for System events. System events, which were introduced in JSF 2.0,
provide an elegant view on the JSF life cycle. Using System event listeners, the JSF developer can, for example, write
custom code that will be executed in the application startup and teardown events or be executed when an exception is
thrown in the application.
SystemEventListener is the main interface for System event listeners. SystemEventListener can listen for
all SystemEvents types. System events can be triggered on the JSF application level (like application startup or
application teardown or application exception) or on the JSF component level (like “before validating the component”
or “after validating the component” or “before the view is rendered”). If System events occur on the component level,
then in this case you may use the more specific event listener, which is ComponentSystemEventListener interface
(shown in Figure 4-2 ) to handle. This is because ComponentSystemEventListener listens for ComponentSystemEvent
(which extends SystemEvent ).