Develop session management in servlets
This information, combined with the coding example SessionSample.java, provides a programming model for implementing sessions in our own servlets.
- Get the HttpSession object.
To obtain a session, use the getSession method of the javax.servlet.http.HttpServletRequest object in the Java Servlet 3.0 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.
Deprecated feature: Session tracking using the SSL ID is deprecated in WebSphere Application Server version 7.0. We can configure session tracking to use cookies or modify the application to use URL rewritingdepfeat
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 and later, 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.)
- Store and retrieve user-defined data in the session.
After a session is established, we 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. We 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.
- Optional. Output an HTML response page containing
data from the HttpSession object.
- 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 returned to the user and
displays the value of the sessiontest.counter each time the user visits
that
web page during the session.
- 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.
- End the session. We 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.
- 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.
Example
import java.io.*;
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
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<head><title>Session Tracking Test</title></head>");
out.println("<body>");
out.println("<h1>Session Tracking Test</h1>");
out.println ("You have hit this page " + ival + " times" + "<br>");
out.println ("Your " + request.getHeader("Cookie"));
out.println("</body></html>");
}
}
Related concepts