How do I know session last access time?

By Wayan in Servlet 1 Comment 
package org.kodejava.servlet;

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;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;

@WebServlet(name = "SessionLastAccessTime", urlPatterns = "/last-access-time")
public class SessionLastAccessTime extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        HttpSession session = request.getSession();
        Date date = new Date(session.getLastAccessedTime());

        PrintWriter writer = response.getWriter();
        writer.println("Last accessed time: " + date);
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }
}

This servlet will return a result like:

Last accessed time: Mon Sep 27 06:43:03 CST 2021

Maven dependencies

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
</dependency>

Maven Central

How do I get a notification when session attribute was changed?

By Wayan in Servlet 0 Comment

Implementing the HttpSessionAttributeListener will make the servlet container inform you about session attribute changes. The notification is in a form of HttpSessionBindingEvent object. The getName() on this object tell the name of the attribute while the getValue() method tell about the value that was added, replaced or removed.

package org.kodejava.servlet;

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

@WebListener
public class SessionAttributeListener implements HttpSessionAttributeListener {

    @Override
    public void attributeAdded(HttpSessionBindingEvent event) {
        // This method is called when an attribute is added to a session.
        // The line below display session attribute name and its value.
        System.out.println("Session attribute added: ["
                + event.getName() + "] = [" + event.getValue() + "]");
    }

    @Override
    public void attributeRemoved(HttpSessionBindingEvent event) {
        // This method is called when an attribute is removed from a session.
        System.out.println("Session attribute removed: ["
                + event.getName() + "] = [" + event.getValue() + "]");
    }

    @Override
    public void attributeReplaced(HttpSessionBindingEvent event) {
        // This method is invoked when an attribute is replaced in a session.
        System.out.println("Session attribute replaced: ["
                + event.getName() + "] = [" + event.getValue() + "]");
    }
}

Maven dependencies

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
</dependency>

Maven Central

How do I capture session creation and removal events?

By Wayan in Servlet 0 Comment

The Servlet specification define an HttpSessionListener interface that can be implemented if we want to listen to session creation and removal events. The interface has two methods that we can implement, the sessionCreated(HttpSessionEvent event) and sessionDestroyed(HttpSessionEvent event) methods. To activate the listener we need to register it in the servlet container. To register the listener we can use the @WebListener annotation. Let’s see the full code snippet below.

package org.kodejava.servlet;

import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import java.util.Date;

@WebListener
public class MySessionListener implements HttpSessionListener {

    // Notification that a new session was created
    @Override
    public void sessionCreated(HttpSessionEvent event) {
        HttpSession session = event.getSession();

        System.out.println("New session created  : " + session.getId());
        System.out.println("Session creation time: " + new Date(session.getCreationTime()));
    }

    // Notification that a session was invalidated
    @Override
    public void sessionDestroyed(HttpSessionEvent event) {
        HttpSession session = event.getSession();

        System.out.println("Session destroyed  : " + session.getId());
    }
}

Maven dependencies

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
</dependency>

Maven Central

How do I invalidate user’s session?

By Wayan in Servlet 0 Comment

In a web application you might want to invalidate user session, for instance in a logout Servlet or JSP. There is an invalidate() method in the HttpSession interface, this method invalidates the session, and it removes all attributes from the session object.

package org.kodejava.servlet;

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;
import java.io.IOException;

@WebServlet(name = "InvalidateSessionServlet", urlPatterns = "/invalidate-session")
public class InvalidateSessionServlet extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        HttpSession session = request.getSession();

        // Invalidate the session and removes any attribute related to it
        session.invalidate();

        // Get an HttpSession related to this request, if no session exist don't
        // create a new one. This is just a check to see after invalidation the
        // session will be null.
        session = request.getSession(false);

        response.getWriter().println("Session : " + session);
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }
}

Maven dependencies

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
</dependency>

Maven Central

How do I get client IP and hostname in Servlet?

By Wayan in Servlet 0 Comment 
package org.kodejava.servlet;

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

@WebServlet(name = "ClientAddressServlet", urlPatterns = "/client-ip")
public class ClientAddressServlet extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // Get client's IP address
        String clientIP = request.getRemoteAddr();

        // Get client's host name
        String clintHost = request.getRemoteHost();

        response.setContentType("text/plain");
        PrintWriter out = response.getWriter();
        out.println("IP  : " + clientIP);
        out.println("Host: " + clintHost);
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }
}

Maven dependencies

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
</dependency>

Maven Central