JSF - valueChangeListener


Advertisements


When the user interacts with input components, such as h:inputText or h:selectOneMenu, the JSF fires a valueChangeEvent, which can be handled in two ways.

S.No Technique & Description
1

Method Binding

Pass the name of the managed bean method in valueChangeListener attribute of UI Component.

2

ValueChangeListener

Implement ValueChangeListener interface and pass the implementation class name to valueChangeListener attribute of UI Component.

Method Binding

Define a method

public void localeChanged(ValueChangeEvent e) { 
  
   //assign new value to country 
   selectedCountry = e.getNewValue().toString();  
} 

Use the above method

<h:selectOneMenu value = "#{userData.selectedCountry}"  onchange = "submit()" 
   valueChangeListener = "#{userData.localeChanged}" >
   <f:selectItems value = "#{userData.countries}" />
</h:selectOneMenu>

ValueChangeListener

Implement ValueChangeListener

public class LocaleChangeListener implements ValueChangeListener {
   
   @Override
   public void processValueChange(ValueChangeEvent event)
      throws AbortProcessingException {
     
      //access country bean directly
      UserData userData = (UserData) FacesContext.getCurrentInstance().
      getExternalContext().getSessionMap().get("userData"); 
      userData.setSelectedCountry(event.getNewValue().toString());
   }
}

Use listener method

<h:selectOneMenu value = "#{userData.selectedCountry}" onchange = "submit()">
   <f:valueChangeListener type = "com.tutorialspoint.test.LocaleChangeListener"
      />
   <f:selectItems value = "#{userData.countries}" />
</h:selectOneMenu>

Example Application

Let us create a test JSF application to test the valueChangeListener in JSF.

Step Description
1 Create a project with a name helloworld under a package com.tutorialspoint.test as explained in the JSF - First Application chapter.
2 Modify UserData.java file as explained below.
3 Create LocaleChangeListener.java file under a package com.tutorialspoint.test. Modify it as explained below.
4 Modify home.xhtml as explained below. Keep the rest of the files unchanged.
5 Compile and run the application to make sure the business logic is working as per the requirements.
6 Finally, build the application in the form of war file and deploy it in Apache Tomcat Webserver.
7 Launch your web application using appropriate URL as explained below in the last step.

UserData.java

package com.tutorialspoint.test;

import java.io.Serializable;
import java.util.LinkedHashMap;
import java.util.Map;

import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;
import javax.faces.event.ValueChangeEvent;

@ManagedBean(name = "userData", eager = true)
@SessionScoped
public class UserData implements Serializable {
   private static final long serialVersionUID = 1L;
   private static Map<String,String> countryMap;
   private String selectedCountry = "United Kingdom"; //default value 

   static {
      countryMap = new LinkedHashMap<String,String>();
      countryMap.put("en", "United Kingdom"); //locale, country name
      countryMap.put("fr", "French");
      countryMap.put("de", "German");	
   }

   public void localeChanged(ValueChangeEvent e) {
      //assign new value to country
      selectedCountry = e.getNewValue().toString(); 
   }

   public Map<String, String> getCountries() {
      return countryMap;
   }

   public String getSelectedCountry() {
      return selectedCountry;
   }

   public void setSelectedCountry(String selectedCountry) {
      this.selectedCountry = selectedCountry;
   }
}

LocaleChangeListener.java

package com.tutorialspoint.test;

import javax.faces.context.FacesContext;
import javax.faces.event.AbortProcessingException;
import javax.faces.event.ValueChangeEvent;
import javax.faces.event.ValueChangeListener;

public class LocaleChangeListener implements ValueChangeListener {
   
   @Override
   public void processValueChange(ValueChangeEvent event)
      throws AbortProcessingException {
      
      //access country bean directly
      UserData userData = (UserData) FacesContext.getCurrentInstance().
      getExternalContext().getSessionMap().get("userData");
      userData.setSelectedCountry(event.getNewValue().toString());
   }
}

home.xhtml

<?xml version = "1.0" encoding = "UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns = "http://www.w3.org/1999/xhtml"   
   xmlns:h = "http://java.sun.com/jsf/html"
   xmlns:f = "http://java.sun.com/jsf/core">
   
   <h:head>
      <title>JSF tutorial</title>		   
   </h:head>
   
   <h:body> 
      <h2>valueChangeListener Examples</h2>
      
      <h:form>
         <h2>Method Binding</h2>
         <hr/>
         <h:panelGrid columns = "2">
            Selected locale :
            <h:selectOneMenu value = "#{userData.selectedCountry}"
               onchange = "submit()"
               valueChangeListener = "#{userData.localeChanged}" >
               <f:selectItems value = "#{userData.countries}" />
            </h:selectOneMenu>
            Country Name: 		 
            <h:outputText id = "country" value = "#{userData.selectedCountry}"
            size = "20" />		
         </h:panelGrid>
      </h:form>
   
   </h:body>
</html>

Once you are ready with all the changes done, let us compile and run the application as we did in JSF - First Application chapter. If everything is fine with your application, this will produce the following result.

JSF valueChangeListener result

Select locale. You will see the following result.

JSF valueChangeListener result1

Modify home.xhtml again in the deployed directory where you've deployed the application as explained below. Keep the rest of the files unchanged.

home.xhtml

<?xml version = "1.0" encoding = "UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns = "http://www.w3.org/1999/xhtml"   
   xmlns:h = "http://java.sun.com/jsf/html"
   xmlns:f = "http://java.sun.com/jsf/core">
   
   <h:head>
      <title>JSF tutorial</title>		   
   </h:head>
   
   <h:body> 
      <h2>valueChangeListener Examples</h2>
      
      <h:form>    
         <h2>ValueChangeListener interface</h2>
         <hr/>
         <h:panelGrid columns = "2">
            Selected locale :
            <h:selectOneMenu value = "#{userData.selectedCountry}"
               onchange = "submit()">
               <f:valueChangeListener 
                  type = "com.tutorialspoint.test.LocaleChangeListener" />
               <f:selectItems value = "#{userData.countries}" />
            </h:selectOneMenu>
            Country Name: 		 
            <h:outputText id = "country1" value = "#{userData.selectedCountry}"
               size = "20" />		
         </h:panelGrid>
      </h:form>
   
   </h:body>
</html>

Once you are ready with all the changes done, refresh the page in the browser. If everything is fine with your application, this will produce the following result.

JSF valueChangeListener result2

Select locale. You will see the following result.

JSF valueChangeListener result3
jsf_event_handling.htm

Advertisements