Servlets : HttpSession Listener Demo [Count logged in Users]

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HttpSessionListenerDemo Project Dir Structure

LoginServlet.java

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

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class LoginServlet extends HttpServlet
{
    
    private static final long serialVersionUID = 1L;

    public void init() throws ServletException
    {
        System.out.println("-----------------------------------------");
        System.out.println(" Init method is called in "
                + this.getClass().getName());
        System.out.println("--------------------------------------");
    }
    
    public void doGet( HttpServletRequest request, HttpServletResponse response )
            throws ServletException, IOException
    {

        response.setContentType("text/html");
        PrintWriter out = response.getWriter();

        String userName = request.getParameter("username");
        out.print("Welcome " + userName);

        HttpSession session = request.getSession();
        session.setAttribute("uname", userName);

        ServletContext ctx = getServletContext();
        int totalUsers = (Integer) ctx.getAttribute("totalusers");
        int currentUsers = (Integer) ctx.getAttribute("currentusers");
        
        out.print("<br>total users= " + totalUsers);
        out.print("<br>current users= " + currentUsers);

        out.print("<br><a href='logout'>logout</a>");

        out.close();
    }
    
    public void destroy()
    {
        System.out.println("-----------------------------------------");
        System.out.println(" destroy method is called in "
                + this.getClass().getName());
        System.out.println("-----------------------------------------");
    }

}

LogoutServlet.java

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

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

public class LogoutServlet extends HttpServlet
{

    private static final long serialVersionUID = 1L;

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

        response.setContentType("text/html");
        PrintWriter out = response.getWriter();

        HttpSession session = request.getSession(false);
        session.invalidate();

        out.print("You are successfully logged out");

        out.close();
    }

}

CountUserListener.java

import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class CountUserListener implements HttpSessionListener
{
    ServletContext ctx = null;
    static int     totalUserCount = 0, currentUserCount = 0;

    public void sessionCreated( HttpSessionEvent httpSessionEvent )
    {
        System.out.println("sessionCreated method has been called in "
                + this.getClass().getName());

        
        totalUserCount++;
        currentUserCount++;

        ctx = httpSessionEvent.getSession().getServletContext();
        
        ctx.setAttribute("totalusers", totalUserCount);
        ctx.setAttribute("currentusers", currentUserCount);

    }

    public void sessionDestroyed( HttpSessionEvent httpSessionEvent )
    {
        
        System.out.println("sessionDestroyed method has been called in "
                + this.getClass().getName());       
        currentUserCount--;
        ctx.setAttribute("currentusers", currentUserCount);
    }

}

web.xml

<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    metadata-complete="true" version="3.0">
    <display-name>HttpSessionListenerDemo</display-name>
    <description>
        This is a simple web application with a source code organization
        based on the recommendations of the Application Developer's Guide.
    </description>


    <servlet>
        <servlet-name>LoginServlet</servlet-name>
        <servlet-class>LoginServlet</servlet-class>
    </servlet>
    
    <servlet>
        <servlet-name>LogoutServlet</servlet-name>
        <servlet-class>LogoutServlet</servlet-class>
    </servlet>


    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/login</url-pattern>
    </servlet-mapping>
    
    <servlet-mapping>
        <servlet-name>LogoutServlet</servlet-name>
        <url-pattern>/logout</url-pattern>
    </servlet-mapping>


    <listener>
        <listener-class>CountUserListener</listener-class>
    </listener>
    
</web-app>

index.html

<form action="login">
    Name:<input type="text" name="username"><br> 
    
    Password:<input type="password" name="password"><br> 
    
    <input type="submit" value="login" />
    
</form>

Environment Used 

JDK version :1.7.0_51
Tomcat version : 7.0.50 

To Download HttpSessionListenerCountUserDemoApp Project Click the below link

https://sites.google.com/site/javaee4321/servlets/HttpSessionListenerCountUserDemoApp.zip?attredirects=0&d=1

See also:

Servlets Tutorial

All Design Patterns Links