HttpSessionAttributeListener Example

By admin | December 07, 2011 | Updated : July 22, 2020 listener, servlet, No Comments

HttpSessionAttributeListener Example explains about how to use HttpSessionAttributeListener in a web application.

HttpSessionAttributeListener is an interface which is extending from the base interface java.util.EventListener. HttpSessionAttributeListener will be informed by the web container when there is a change to the attributes of a web application's session, like an attribute is added in a session or an attribute is removed or an attribute is replaced by another attribute etc.

HttpSessionAttributeListener interface has following methods:

attributeAdded(HttpSessionBindingEvent event)
attributeRemoved(HttpSessionBindingEvent event)
attributeReplaced(HttpSessionBindingEvent event)

Example Package Structure

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    version="2.5">
    <listener>
        <listener-class>com.listener.HttpSessionAttributeListenerExample</listener-class>
    </listener>
</web-app>

HttpSessionAttributeListenerExample.java

package com.listener;

import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;

public class HttpSessionAttributeListenerExample implements HttpSessionAttributeListener {

@Override
public void attributeAdded(HttpSessionBindingEvent event) {
    String attributeName = event.getName();
    Object attributeValue = event.getValue();
    System.out.println("Attribute added : " + attributeName + " : " + attributeValue);
}

@Override
public void attributeRemoved(HttpSessionBindingEvent event) {
    String attributeName = event.getName();
    Object attributeValue = event.getValue();
    System.out.println("Attribute removed : " + attributeName + " : "+ attributeValue);
}

@Override
public void attributeReplaced(HttpSessionBindingEvent event) {
    String attributeName = event.getName();
    Object attributeValue = event.getValue();
    System.out.println("Attribute replaced : " + attributeName + " : "+ attributeValue);
}
}

Servlet Usage

HttpSession session = request.getSession();
//When new session attribute is created then attributeAdded() is executed
session.setAttribute("url", "javatips.net");
//When session attribute is replaced then attributeReplaced() is executed
session.setAttribute("url", "www.javatips.net");
//When session attribute removed then attributeRemoved() is executed
session.removeAttribute("url");

Note

From Servlet API 3.0, we can use javax.servlet.annotation, so that web.xml is not necessary

Here we are using @WebListener annotation

HttpSessionAttributeListenerExample.java

package com.listener;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;

@WebListener
public class HttpSessionAttributeListenerExample implements HttpSessionAttributeListener {

@Override
public void attributeAdded(HttpSessionBindingEvent event) {
    String attributeName = event.getName();
    Object attributeValue = event.getValue();
    System.out.println("Attribute added : " + attributeName + " : " + attributeValue);
}

@Override
public void attributeRemoved(HttpSessionBindingEvent event) {
    String attributeName = event.getName();
    Object attributeValue = event.getValue();
    System.out.println("Attribute removed : " + attributeName + " : "+ attributeValue);
}

@Override
public void attributeReplaced(HttpSessionBindingEvent event) {
    String attributeName = event.getName();
    Object attributeValue = event.getValue();
    System.out.println("Attribute replaced : " + attributeName + " : "+ attributeValue);
}
}

ListenerServletExample.java

package com.listener;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
* This servlet is used for showing an example about sessionListener
*/
@WebServlet("/ListenerServletExample")
public class ListenerServletExample extends HttpServlet {
    private static final long serialVersionUID = 1L;

   public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

       HttpSession session = request.getSession();
     //When new session attribute is created then attributeAdded() is executed
     session.setAttribute("url", "javatips.net");
     //When session attribute is replaced then attributeReplaced() is executed
     session.setAttribute("url", "www.javatips.net");
     //When session attribute removed then attributeRemoved() is executed
     session.removeAttribute("url");

       PrintWriter out = response.getWriter();
       out.append("Session Created Successfully");
    }
}

Tomcat Console Output

Attribute added : url : javatips.net
Attribute replaced : url : www.javatips.net
Attribute removed : url : javatips.net

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Example Package Structure

web.xml

HttpSessionAttributeListenerExample.java

Servlet Usage

HttpSessionAttributeListenerExample.java

ListenerServletExample.java

Tomcat Console Output

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