JSP Servlet Session Listener tutorial example in Eclipse & Tomcat
- By Viral Patel on August 14, 2009
- J2EE
Listener is one of the most popular technologies used in the J2EE web application. It is part of the Java Servlet as defined in Servlet 2.3 but they have their own specific functionalities. There are two most widely used Servlet Listener i.e. ServletContextListener and HttpSessionListener.
Let us create a Servlet Listener that just counts the number of running http sessions and prints the details whenever a session gets created or destroy.
We will use Eclipse for developing our application and Apache Tomcat for deploying and running our application.
Step 1: Create dynamic web project in Eclipse
Create Dynamic Web Project in Eclipse and name it SessionListener
Starts eclipse and create a new dynamic web project with name SessionListener. Select Target runtime environment. I have selected Apache Tomcat v6.0, you can select any Tomcat version that you have installed. Click on Finish.
Step 2: Create package & HTTP Session Listener class
Create package and session listener class
Create a package for Session Listener in your source folder of Project. I have created a package net.viralpatel.servlet.listener. Inside the package, create a Java class file called SessionListener.java.
Copy following content into newly created SessionListener class.
SessionListener.java
package net.viralpatel.servlet.listener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public class SessionListener implements HttpSessionListener {
private int sessionCount = 0;
public void sessionCreated(HttpSessionEvent event) {
synchronized (this) {
sessionCount++;
}
System.out.println("Session Created: " + event.getSession().getId());
System.out.println("Total Sessions: " + sessionCount);
}
public void sessionDestroyed(HttpSessionEvent event) {
synchronized (this) {
sessionCount--;
}
System.out.println("Session Destroyed: " + event.getSession().getId());
System.out.println("Total Sessions: " + sessionCount);
}
}
In this listener example, we have implemented an interface javax.servlet.http.HttpSessionListener and override its methods sessionCreated and sessionDestroyed.
The sessionCreated() method will be called by the servlet container whenever a new session is created for this application. An object of javax.servlet.http.HttpSessionEvent class is passed as an argument to the sessionCreated method. This object can be used to get the session related information including session ID. In our example we have used a counter sessionCounter which counts the number of live session at any given point of time. Whenever a new session is created, this count gets incremented.
The sessionDestroyed() method will be called by the servlet container whenever an existing session is invalidated. We have used this method in our example to decrement the session count and display the ID of session being destroyed.
Step 3: Create Http Session Listener entry in Web.xml
Open Web.xml file from WEB-INF directory of your Project and add following entry for listener tag.
<listener> <description>sessionListener</description> <listener-class> net.viralpatel.servlet.listener.SessionListener </listener-class> </listener>
In this entry, we have added SessionListener class in Web xml. Hence for every session creation and invalidation, the methods will be called by servlet container.
Step 4: Create JSP files for session tracking
We will create a small web application to test the functionality of Session Listener. There will be 3 JSP files, index.jsp will display a list of users. These users are stored in a session variable. The AddUser.jsp will add the user in the session variable. And the DestroySession.jsp will invalidate the session. Create three JSPs and copy following content into it.
index.jsp
<%@page import="java.util.List"%>
<%@page import="java.util.ArrayList"%>
<html>
<head>
<title>Servlet Session Listener example - viralpatel.net</title>
</head>
<body>
<h2>Add User Screen</h2>
<span style="float: right">
<a href="DestroySession.jsp">Destroy this session</a>
</span>
<form method="post" action="AddUser.jsp">
<h3>Enter Username to Add in List</h3>
<input type="text" name="user"/>
<input type="submit" value="Add User"/>
</form>
<%
List<String> users = (List<String>)session.getAttribute("users");
for(int i=0; null!=users && i < users.size(); i++) {
out.println("<br/>" + users.get(i));
}
%>
</body>
</html>
AddUser.jsp
<%@page import="java.util.ArrayList"%>
<%@page import="java.util.List"%>
<%
String username = request.getParameter("user");
List<String> users = (List<String>)session.getAttribute("users");
if(null == users) {
users = new ArrayList<String>();
}
users.add(username);
session.setAttribute("users", users);
response.sendRedirect("index.jsp");
%>
DestroySession.jsp
<% session.invalidate(); %> <h2>Session Destroyed successfully.. </h2> <a href="javascript:history.back()">Click here to go Back</a>
Step 5: Execute the web application
We are done with the coding part of HTTP Session Listener example. Now execute the project by Run -> Run As -> Run on server (shortcut Alt+Shift+X, R).
Check the console you will see the output that we print using System.out.
Add users and see the list of users added and also check the console output to see the logs for session creation and session count.
Once you click Destroy Session, the session gets invalidated and the session count is decremented.
Download Source code
Download WAR file with Source code (4.14kb)
Feel free to change the code and experiment with session listener
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Hi Veeral,
in index.jsp , for the line List user = (List)session.getAttribute(“username”); it says “Type safety: Unchecked cast from Object to List” error. ????
Hi Veeral,
sorry the above comment has been modified …. for the line List user = (List)session.getAttribute(“username”); it says Type safety: Unchecked cast from Object to List” error. ????
Also, in index.jsp you’ve written, List users = (List)session.getAttribute(“users”);
please explain where did we set the attribute “users” and in this jsp file how would the container know that session is an object of HttpSession as in this file we never declared it ….
Sorry if I am being pain, but I am new …
@digant: session is an implicit object defined by container in JSP. You can directly use it in JSP without declaring it. I will suggest you to refer http://java.sun.com/j2ee/tutorial/1_3-fcs/doc/JSPIntro7.html
The user object is set in session in AddUser.jsp