About this task
This information, combined with the coding example SessionSample.java,
provides a programming model for implementing sessions in your own
servlets.
Procedure
- 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.
You can configure session tracking to use cookies or modify the application
to use URL rewriting
depfeat
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, 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.
- (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 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.
- (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. 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.
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>");
}
}