As explained in Implementing an Event
Listener, events are automatically queued on standard components that
fire events. A custom component, on the other hand, must manually queue
events from its decode
method if it fires events.
Performing Decoding explains how to queue
an event on MapComponent
using its decode
method. This section
explains how to write the class that represents the event of clicking on
the map and how to write the method that processes this event.
As explained in Understanding the Facelets
Page, the actionListener
attribute of the bookstore:map
tag points
to the MapBookChangeListener
class. The listener class’s
processAction
method processes the event of clicking the image map.
Here is the processAction
method:
@Override
public void processAction(ActionEvent actionEvent)
throws AbortProcessingException {
AreaSelectedEvent event = (AreaSelectedEvent) actionEvent;
String current = event.getMapComponent().getCurrent();
FacesContext context = FacesContext.getCurrentInstance();
String bookId = books.get(current);
context.getExternalContext().getSessionMap().put("bookId", bookId);
}
When the JavaServer Faces implementation calls this method, it passes in
an ActionEvent
object that represents the event generated by clicking
on the image map. Next, it casts it to an AreaSelectedEvent
object
(see
tut-install`/examples/case-studies/dukes-bookstore/src/java/dukesbookstore/listeners/AreaSelectedEvent.java`).
Then this method gets the MapComponent
associated with the event.
Next, it gets the value of the MapComponent
object’s current
attribute, which indicates the currently selected area. The method then
uses the value of the current
attribute to get the book’s ID value
from a HashMap
object, which is constructed elsewhere in the
MapBookChangeListener
class. Finally, the method places the ID
obtained from the HashMap
object into the session map for the
application.
In addition to the method that processes the event, you need the event
class itself. This class is very simple to write; you have it extend
ActionEvent
and provide a constructor that takes the component on
which the event is queued and a method that returns the component. Here
is the AreaSelectedEvent
class used with the image map:
public class AreaSelectedEvent extends ActionEvent {
public AreaSelectedEvent(MapComponent map) {
super(map);
}
public MapComponent getMapComponent() {
return ((MapComponent) getComponent());
}
}
As explained in the section Creating Custom
Component Classes, in order for MapComponent
to fire events in the
first place, it must implement ActionSource
. Because MapComponent
extends UICommand
, it also implements ActionSource
.