HTTP is a stateless protocol; each time a client requests for a page, a separate connection is established between the client and the server. Thus, it provides no way for a server to maintain information for a particular user across multiple requests. There are many web applications where it is required to maintain this information. For example, in case of shopping cart, it is required to keep track of the list of items that are added in each user’s cart. For this, the server must provide a way to store data for each client and distinguish clients from one another.
Session provides such mechanism. A session consists of all the requests that are made during invocation of a single browser. The servlet manages the session using HttpSession interface. Using this interface, a session can be created between an HTTP client and an HTTP server. This session exists for a specified period of time across a sequence of requests from a user.
A servlet to keep track of the number of times a user has visited a site during the current session using interface HttpSession
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
public class SessionTrackingExample extends HttpServlet
{
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
HttpSession session= request.getSession(true);
// Create a session object if does not exist
Date createTime =new Date(session.getCreationTime());
// Get session creation time
Date lastAccessTime = new Date(session.getLastAccessedTime());
// Get sessions last access time
String title = “Welcome Back !”;
Integer visitCounter =new Integer(0);
String userID =new String(“xyz”);
if (session.isNew())
{
title= “Welcome !”;
session.setAttribute(“userID”, userID);
}
else
{
visitCounter = (Integer) session.getAttribute(“visitCount”);
visitCounter = visitCounter + 1;
userID = (String)session.getAttribute(“userID”);
}
session.setAttribute(“visitCount”, visitCounter);
// Check if this is new Visitor
response.setContentType(“text/html”);
PrintWriter out= response.getWriter();
out.println(“<html>\n” +”<head><title>” + title+
“</title></head>\n” + “<body\”>\n” +
“<h1 align=\”center \”>”+title + “</h1>\n” +
“<h2 align=\”center\”>Session Details</h2>\n” +
“<table border=\”1\” align=\”center\”>\n” +
“<tr\”>\n” +
“<th>Session info</th><th>value</th></tr>\n”+
“<tr>\n” + ” <td>Id</td>\n” +
“<td>” + session.getId() + “</td></tr>\n” +
“<tr>\n” +” <td>Session Creation Time</td>\n” +
“<td>” + createTime + ” </td></tr>\n” +
“<tr>\n” + ” <td>Last Accessed at</td>\n” +
“<td>” + lastAccessTime + ” </td></tr>\n” +
“<tr>\n” + ” <td>Visitor ID</td>\n” +
“<td>” + userID + ” </td></tr>\n” +
“<tr>\n” + ” <td>Number of visits</td>\n” +
“<td>” + visitCounter + “</td></tr>\n” +
“</table>\n” + “</body></html>”);
}
}
In this example, a session is created using the getSession () method of HttpServletRequest interface. The single parameter to this method indicates that a new session must be created if it does not exist. This method returns an HttpSession object. To access the properties of session including the session identifier, different methods, namely, getCreationTime(), lastAccessTime(), SetAttribute(), getAttribute(), and get Id ()are invoked using the session object.
Compile the servlet SessionTrackingExample and create appropriate entry in web.xml file. Type the URL https://ecomputernotes.com:8080/SessionTrackingExample in the browser. On first run, it will display the output shown in Figure
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