Introduction to JavaServer Faces Part 2

Writing the ActionListener for the Listener and Component Tree Example

The ActionListener for the command button is the most interesting part of this JSF application. It demonstrates how an event causes a listener to be executed. The listener simply prints messages to the console. However, it shows important information such as the hierarchy of the component tree of the JSP page from which the event was fired and the component that triggered the event. The ActionListener is shown in Listing 5.

Listing 5 The ActionListener for the Command Button (MyActionListener.java)

 
package ch02a; 
import java.util.Iterator; 
import javax.faces.component.UIComponent; 
import javax.faces.context.FacesContext; 
import javax.faces.event.ActionEvent; 
import javax.faces.event.ActionListener; 
import javax.faces.event.PhaseId; 
import javax.faces.tree.Tree; 


public class MyActionListener implements ActionListener { 


  public PhaseId getPhaseId() { 
   System.out.println("getPhaseId called");  
   return PhaseId.APPLY_REQUEST_VALUES; 
} 
 
 public void processAction(ActionEvent event) {   
   System.out.println("processAction called");  
   // the component that triggered the action event 
   UIComponent component = event.getComponent();
   System.out.println(   
    "The id of the component that fired the action event: "   
    + component.getComponentId());   
   // the action command   
   String actionCommand = event.getActionCommand() 
   System.out.println("Action command: " + actionCommand); 


      FacesContext facesContext = FacesContext.getCurrentInstance();
      Tree tree = facesContext.getTree(); 
      UIComponent root = tree.getRoot(); 
      System.out.println("----------- Component Tree ------------");
      navigateComponentTree(root, 0); 
      System.out.println("----------------------------------------"); 
  } 


   private void navigateComponentTree( 
      UIComponent component, int level){ 
      // indent 
      for (int i=0; i<level; i++) 
        System.out.print(" "); 
      // print component id 
      System.out.println(component.getComponentId()); 
      Iterator children = component.getChildren(); 
      // navigate children 
      while (children.hasNext()) { 
         UIComponent child = (UIComponent) children.next();
         navigateComponentTree(child, level + 1); 
       } 
     } 
} 



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!