Implementing Value-Change Listeners
Implementing Value-Change Listeners
Note
You need not create an ActionListener implementation to handle an event that results
solely in navigating to a page and does not perform any other application-specific processing.
See
for information on how to manage
page navigation.
Implementing Value-Change Listeners
A ValueChangeListener implementation must include a
processValueChange(ValueChangeEvent)
method. This method processes the specified
value-change event and is invoked by the JavaServer Faces implementation when the
value-change event occurs. The ValueChangeEvent instance stores the old and the new values
of the component that fired the event.
The NameChanged listener implementation is registered on the name UIInput component on the
bookcashier.jsp
page. This listener stores into session scope the name the user entered in the
text field corresponding to the name component. When the bookreceipt.jsp page is loaded, it
displays the first name inside the message:
"Thank you, {0} for purchasing your books from us."
Here is part of the NameChanged listener implementation:
...
public class NameChanged extends Object implements
ValueChangeListener {
public void processValueChange(ValueChangeEvent event)
throws AbortProcessingException {
if (null != event.getNewValue()) {
FacesContext.getCurrentInstance().
getExternalContext().getSessionMap().
put(
"name", event.getNewValue());
}
}
}
When the user enters the name in the text field, a value-change event is generated, and the
processValueChange(ValueChangeEvent)
method of the NameChanged listener
implementation is invoked. This method first gets the ID of the component that fired the event
from the ValueChangeEvent object. Next, it puts the value, along with an attribute name, into
the session map of the FacesContext instance.
explains how to register
this listener onto a component.
Implementing an Event Listener
The Java EE 5 Tutorial · September 2007
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