Registering Listeners on Components

An application developer can implement listeners as classes or as backing bean methods. If a listener is a backing bean method, the page author references the method from either the component’s valueChangeListener attribute or its actionListener attribute. If the listener is a class, the page author can reference the listener from either a valueChangeListener tag or an actionListener tag, and nest the tag inside the component tag, to register the listener on the component.

Referencing a Method That Handles an Action Event and Referencing a Method That Handles a Value-Change Event describe how a page author uses the valueChangeListener and actionListener attributes to reference backing bean methods that handle events.

This section explains how to register the NameChanged value-change listener and a hypothetical LocaleChange action listener implementation on components. Implementing value-change listeners, and implementing action listeners are advanced topics that are covered in Java EE 6 Tutorial, Volume II: Advanced Topics.

Registering a Value-Change Listener on a Component

AValueChangeListener implementation can be registered on a component that implements EditableValueHolder by nesting a valueChangeListener tag within the component’s tag on the page. The valueChangeListener tag supports two attributes:

• type: References the fully qualified class name of a ValueChangeListener implementation

• binding: References an object that implements ValueChangeListener

One of these attributes must be used to reference the value-change listener. The type attribute can accept a literal or a value expression. The binding attribute can only accept a value expression, which must point to a backing bean property that accepts and returns a ValueChangeListener implementation.

The following example shows a value-change listener registered on a component:

<h:inputText  id="name" size="50" value="#{cashier.name}"
     required="true">    
     <f:valueChangeListener type="listeners.NameChanged" />
</h:inputText>

In the example, the core tag type attribute specifies the custom NameChanged listener as the ValueChangeListener implementation which is registered on the name component.

After this component tag is processed and local values have been validated, its corresponding component instance will queue the ValueChangeEvent that is associated with the specified ValueChangeListener to the component.

The binding attribute is used to bind a ValueChangeListener implementation to a backing bean property. It works in a similar way to the binding attribute supported by the standard converter tags.

Registering an Action Listener on a Component

A page author can register an ActionListener implementation on a Command component by nesting an actionListener tag within the component’s tag on the page. Similarly to the valueChangeListener tag, the actionListener tag supports both the type and binding attributes. One of these attributes must be used to reference the action listener.

Here is an example of commandLink tag, that references an ActionListener implementation rather than a backing bean method:

<h:commandLink id="NAmerica" action="bookstore">
     <f:actionListener type="listeners.LocaleChange" />
</h:commandLink>

The type attribute of the actionListener tag specifies the fully qualified class name of the ActionListener implementation. Similarly to the valueChangeListener tag, the actionListener tag also supports the binding attribute.