Servlet – HttpSessionEvent and HttpSessionListener
Last Updated :
30 Jan, 2022
In Java, HttpSessionEvent is a class, which is representing event notifications for changes or updates to sessions within a web application. Similarly, the interface for this event is HttpSessionListener, which is for receiving notification events about HttpSession lifecycle changes. As a means to, accept these notification events, the implementation of the class must follow one of the following:
- It should be declared in the deployment descriptor of the web application, annotated with WebListener
- It should be registered via one of the addListener methods defined on ServletContext
There are two methods of the HttpSessionListner interface:
- sessionCreated: It receives the notification that a session has been created.
- sessionDestroyed: It receives the notification that a session is almost invalidated.
// Parameter: se – the HttpSessionEvent containing the session
void sessionCreated(HttpSessionEvent se)
// Parameter: se – the HttpSessionEvent containing the session
void sessionDestroyed(ServletContextEvent se)
Example
Count the total and the active sessions, using HttpSessionEvent and HttpSessionListener. Now, we have to create these files:
- index.html
- CountUserListner.java
- LoginServlet.java
- LogoutServlet.java
index.html: Login Credentials
HTML
<!DOCTYPE html>
<html>
<body>
<h2>Login Credentials</h2>
<form action="servlet">
Username:<input type="text" name="username"><br>
Password:<input type="password" name="userpass"><br>
<input type="Submit" value="Sign-in"/>
</form>
</body>
</html>
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CountUserListner.java: This listener class counts the total and active sessions and stores this information as an attribute in the ServletContext object.
Java
import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public class CountUserListener implements HttpSessionListener{
ServletContext scx =null;
static int all =0, active =0;
public void sessionCreated(HttpSessionEvent se)
{
all++;
active++;
scx =se.getSession().getServletContext();
scx.setAttribute("All Users", all);
scx.setAttribute("Active Users", active);
}
public void sessionDestroyed(HttpSessionEvent se)
{
active--;
scx.setAttribute("Active Users", active);
}
}
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LoginServlet.java: This Servlet class creates a session and prints the total and current active users.
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 {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html; charset=UTF-8");
PrintWriter out = response.getWriter();
String str = request.getParameter("Username");
out.print("Welcome "+str);
HttpSession session = request.getSession();
session.setAttribute("Uname",str);
ServletContext scx = getServletContext();
int au = (Integer)scx.getAttribute("All Users");
int acu = (Integer)scx.getAttribute("Active Users");
out.print("<br>All Users = "+au);
out.print("<br>Active Users = "+acu);
out.print("<br><a href='logout'>Logout</a>");
out.close();
}
}
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LogoutServlet.java: This Servlet class invalidates session.
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();
}
}
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