We continue with part two of Chapter 2 of Introduction JavaServer Faces Programming, by Budi Kurniawan (McGraw-Hill/Osborne, ISBN 0-07-222983-7, 2004). This section deals with the ActionListener and Component Tree, as well as validation and navigation for your JSP pages. This chapter prepares you for the next chapters by introducing the JSF Application Programming Interface (API) and the Application Configuration file.
An ActionListener must implement the javax.faces.event.ActionListener interface. It provides the implementations for the getPhaseId and processAction methods. The getPhaseId method must return a javax.faces.event.PhaseId, and its return value determines in which process event step of the request processing lifecycle the listener will be executed. The getPhaseId method in the ActionListener in Listing 5 returns PhaseId.APPLY_REQUEST_VALUES. This will make the ActionListener‘s processAction method be called after the Apply Request Values phase of the request processing lifecycle.
The processAction method accepts the javax.faces.event.ActionEvent object from the Lifecycle object. In the ActionListener in Listing 5, the processAction method first obtains the component that triggered the event by calling the getComponent method of the ActionEvent class, and then it prints the component identifier.
= event.getComponent(); System.out.println( "The id of the component that fired the action event: " + component.getComponentId());
It then prints the action command of the ActionEvent object.
Next, it obtains the instance of the current FacesContext and calls its getTree method to acquire the component tree (an instance of javax.faces.tree.Tree class) representing the request page.
</f:use_faces><f:use_faces>FacesContext facesContext = FacesContext.getCurrentInstance(); Tree tree = facesContext.getTree();
To get the root of the component tree, it calls the getRoot method of the Tree class.
Next, it passes the root to the private method navigateComponentTree, which draws the component tree hierarchy.
Remember: This is part one of the second chapter of JavaServer Faces Programming, by Budi Kurniawan (McGraw-Hill/Osborne, ISBN 0-07-222983). Stay tuned for more helpful chapters from McGraw-Hill/Osborne. Buy this book!