Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial

## Handling Events for Custom Components

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`.

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