Session management in servlets


  1. Get the HttpSession object.

    To obtain a session, use the getSession() method of the javax.servlet.http.HttpServletRequest object in the Java Servlet 2.3 API.

    When you first obtain the HttpSession object, the Session Management facility uses one of three ways to establish tracking of the session: cookies, URL rewriting, or Secure Sockets Layer (SSL) information.

    Assume the Session Management facility uses cookies. In such a case, the Session Management facility creates a unique session ID and typically sends it back to the browser as a cookie. Each subsequent request from this user (at the same browser) passes the cookie containing the session ID, and the Session Management facility uses this ID to find the user's existing HttpSession object.

    In Step 1 of the code sample, the Boolean(create) is set to true so that the HttpSession object is created if it does not already exist. (With the Servlet 2.3 API, the javax.servlet.http.HttpServletRequest.getSession() method with no boolean defaults to true and creates a session if one does not already exist for this user.)

  2. Store and retrieve user-defined data in the session.

    After a session is established, you can add and retrieve user-defined data to the session. The HttpSession object has methods similar to those in java.util.Dictionary for adding, retrieving, and removing arbitrary Java objects.

    In Step 2 of the code sample, the servlet reads an integer object from the HttpSession, increments it, and writes it back. You can use any name to identify values in the HttpSession object. The code sample uses the name sessiontest.counter.

    Because the HttpSession object is shared among servlets that the user might access, consider adopting a site-wide naming convention to avoid conflicts.

  3. (Optional) Output an HTML response page containing data from the HttpSession object.
  4. Provide feedback to the user that an action has taken place during the session. You may want to pass HTML code to the client browser indicating that an action has occurred. For example, in step 3 of the code sample, the servlet generates a Web page that is returned to the user and displays the value of the sessiontest.counter each time the user visits that Web page during the session.
  5. (Optional) Notify Listeners. Objects stored in a session that implement the javax.servlet.http.HttpSessionBindingListener interface are notified when the session is preparing to end and become invalidated. This notice enables you to perform post-session processing, including permanently saving the data changes made during the session to a database.
  6. End the session. You can end a session:
    • Automatically with the Session Management facility if a session is inactive for a specified time. The administrators provide a way to specify the amount of time after which to invalidate a session.
    • By coding the servlet to call the invalidate() method on the session object.

import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class SessionSample extends HttpServlet {
public void doGet (HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

// Step 1: Get the Session object

boolean create = true;
HttpSession session = request.getSession(create);

// Step 2: Get the session data value

Integer ival = (Integer)
session.getAttribute ("sessiontest.counter");
if (ival == null) ival = new Integer (1);
else ival = new Integer (ival.intValue () + 1);
session.setAttribute ("sessiontest.counter", ival);

// Step 3: Output the page

PrintWriter out = response.getWriter();
out.println("<head><title>Session Tracking Test</title></head>");
out.println("<h1>Session Tracking Test</h1>");
out.println ("You have hit this page " + ival + " times" + "<br>");
out.println ("Your " + request.getHeader("Cookie"));