- The HttpSessionEvent is notified when session object is changed. The
corresponding Listener interface for this event is HttpSessionListener.
- We
can perform some operations at this event such as counting total and
current logged-in users, maintaing a log of user details such as login
time, logout time etc.
Constructor of HttpSessionEvent class
- HttpSessionEvent(HttpSession source): Construct a session event from the given source.
Method of HttpSessionEvent class
- public HttpSession getSession(): Return the session that changed
Methods of HttpSessionListener interface
- public void
sessionCreated(HttpSessionEvent e): is invoked when session
object is created.
- public
void sessionDestroyed(ServletContextEvent e): is
invoked when session is invalidated.
In this example, are counting the total and current logged-in users. For this purpose, we have created three files:
Login.html: to get input from the user.
MyListener.java: A listener class that counts total and current logged-in users and stores this
information in ServletContext object as an attribute.
First.java: A Servlet class that creates session and prints the total and current logged-in users.
Logout.java: A Servlet class that invalidates session.
web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<listener>
<listener-class>CountUserListener</listener-class>
</listener>
<servlet>
<servlet-name>First</servlet-name>
<servlet-class>First</servlet-class>
</servlet>
<servlet>
<servlet-name>LogoutServlet</servlet-name>
<servlet-class>LogoutServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>First</servlet-name>
<url-pattern>/servlet1</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>LogoutServlet</servlet-name>
<url-pattern>/logout</url-pattern>
</servlet-mapping>
</web-app>
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 total=0,current=0;
public void sessionCreated(HttpSessionEvent e) {
total++;
current++;
ctx=e.getSession().getServletContext();
ctx.setAttribute("totalusers", total);
ctx.setAttribute("currentusers", current);
}
public void sessionDestroyed(HttpSessionEvent e) {
current--;
ctx.setAttribute("currentusers",current);
}
}
Login.html
<form action="servlet1">
Name:<input type="text" name="username"><br>
Password:<input type="password" name="userpass"><br>
<input type="submit" value="login"/>
</form>
First .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 First extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String n=request.getParameter("username");
out.print("Welcome "+n);
HttpSession session=request.getSession();
session.setAttribute("uname",n);
ServletContext ctx=getServletContext();
int t=(Integer)ctx.getAttribute("totalusers");
int c=(Integer)ctx.getAttribute("currentusers");
out.print("<br>total users= "+t);
out.print("<br>current users= "+c);
out.print("<br><a href='logout'>logout</a>");
out.close();
}
}
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 {
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();
}
}
