JSF 2 - Dynamically manipulating the component tree with system events

Let's suppose we want to modify the metadata (attributes)  of elements such as render, requried, maxlength but we do not define in JSF tags. The manipulating components can be conducted in Drools files, for example. How could we do? I think that is what we need to change something of component tree during JSF life-cycle.

JSF supports event handling throughout the JSF life-cycle. In this post, I use two events: postAddToView for scanning components tree and preRenderView for manipulating the meta of components before rendering to GUI.

I modified my own project from previous post for this example. This is my first further JSF trying out with the project as I said before. :)

We define the tags f:event below the form - a container component of the components which we want to work on. The valid values for the attribute type for f:event can be found from tag library document of JSF 2.

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml"
 xmlns:f="http://java.sun.com/jsf/core"
 xmlns:h="http://java.sun.com/jsf/html">
 <h:head>
  <title>JSF - System events Example</title>
 </h:head>
 <h:body>
  <h:form id="helloForm">
   <f:event listener="#{guiHanlder.onScanView}" type="postAddToView"/>
   <f:event listener="#{guiHanlder.onManipulateView}" type="preRenderView"/>
   
   <h:outputText value="#{helloBean.greeting}" id="greetingOutputTxt"/>
   <br/>
   <h:inputText value="#{helloBean.name}" id="nameInputText"/>
  </h:form>
 </h:body>
</html>

This is the managed bean below is just used for displaying information.

package vn.nvanhuong.jsf_myfaces;

import javax.faces.bean.ManagedBean;

@ManagedBean(name = "helloBean")
public class HelloManagedBean {
 private String greeting;
 private String name;
 
 public String getGreeting() {
  return greeting;
 }

 public void setGreeting(String greeting) {
  this.greeting = greeting;
 }

 public String getName() {
  return name;
 }

 public void setName(String name) {
  this.name = name;
 }
}

Here, I just used a method from a Java class to manipulate the components. In my future posts, I am going to try to call a Drools files instead.

package vn.nvanhuong.jsf_myfaces;

import java.util.List;

import javax.faces.bean.ManagedBean;
import javax.faces.component.UIComponent;
import javax.faces.component.html.HtmlInputText;
import javax.faces.component.html.HtmlOutputText;
import javax.faces.event.PostAddToViewEvent;
import javax.faces.event.PreRenderViewEvent;

@ManagedBean(name = "guiHanlder")
public class GuiManipulatingHandler {
 private List uiComponents;
 
 public void onScanView(PostAddToViewEvent event) {
  UIComponent rootView = event.getComponent();
  uiComponents = rootView.getChildren();
 }

 public void onManipulateView(PreRenderViewEvent event) {
  for (UIComponent uiComponent : uiComponents) {
   if(uiComponent instanceof HtmlOutputText){
    ((HtmlOutputText) uiComponent).setValue("Hello");
   }
   if(uiComponent instanceof HtmlInputText){
    ((HtmlInputText) uiComponent).setMaxlength(100);
    ((HtmlInputText) uiComponent).setValue("JSF system events");
   }
  }
 }
}

I ran on Tomcat (v7) and the result looks like:

Source code: https://github.com/vnnvanhuong/jsf_myfaces/tree/jsf_system_events

Reference:
[1]. http://balusc.omnifaces.org/2006/09/debug-jsf-lifecycle.html