Session tracking options


There are several options for session tracking, depending on what sort of tracking method you want to use...


Session tracking with cookies

Tracking sessions with cookies is the default. No special programming is required to track sessions with cookies.


Session tracking with URL rewriting

An application that uses URL rewriting to track sessions must adhere to certain programming guidelines. The application developer needs to do the following...

Using URL rewriting also requires that you enable URL rewriting in the Session Management facility.

Note that In certain cases, clients cannot accept cookies. Therefore, you cannot use cookies as a session tracking mechanism. Applications can use URL rewriting as a substitute.


Program session servlets to encode URLs

Depending on whether the servlet is returning URLs to the browser or redirecting them, include either encodeURL( ) or encodeRedirectURL( ) in the servlet code. Examples demonstrating what to replace in your current servlet code follow.


Rewrite URLs to return to the browser

Suppose you currently have this statement

out.println("<a href=\"/store/catalog\">catalog<a>");

Change the servlet to call the encodeURL method before sending the URL to the output stream

out.println("<a href=\"");
out.println(response.encodeURL ("/store/catalog"));


Rewrite URLs to redirect

Suppose you currently have the following statement

response.sendRedirect ("http://myhost/store/catalog");

Change the servlet to call the encodeRedirectURL method before sending the URL to the output stream

response.sendRedirect (response.encodeRedirectURL ("http://myhost/store/catalog"));

The encodeURL() and encodeRedirectURL() methods are part of the HttpServletResponse object. These calls check to see if URL rewriting is configured before encoding the URL. If it is not configured, the calls return the original URL.

If both cookies and URL rewriting are enabled and response.encodeURL() or encodeRedirectURL() is called, the URL is encoded, even if the browser making the HTTP request processed the session cookie.

You can also configure session support to enable protocol switch rewriting. When this option is enabled, the product encodes the URL with the session ID for switching between HTTP and HTTPS protocols.


Supply a servlet or JSP file as an entry point

The entry point to an application (such as the initial screen presented) may not require the use of sessions. However, if the application in general requires session support (meaning some part of it, such as a servlet, requires session support), then after a session is created, all URLs are encoded to perpetuate the session ID for the servlet (or other application component) requiring the session support.

The following example shows how you can embed Java code within a JSP file

response.encodeURL ("/store/catalog");


Session tracking with SSL information

No special programming is required to track sessions with SSL information.

To use SSL information, turn on Enable SSL ID tracking in the Session Management property page. Because the SSL session ID is negotiated between the Web browser and HTTP server, this ID cannot survive an HTTP server failure. However, the failure of an appserver does not affect the SSL session ID if an external HTTP Server is present between WAS and the browser.

SSL tracking is supported for the IBM HTTP Server and iPlanet Web servers only. You can control the lifetime of an SSL session ID by configuring options in the Web server. For example, in the IBM HTTP Server, set the configuration variable SSLV3TIMEOUT to provide an adequate lifetime for the SSL session ID. An interval that is too short can cause a premature termination of a session. Also, some Web browsers might have their own timers that affect the lifetime of the SSL session ID. These Web browsers may not leave the SSL session ID active long enough to serve as a useful mechanism for session tracking. Internal Http Server of WebSphere also supports SSL Tracking.

When using the SSL session ID as the session tracking mechanism in a cloned environment, use either cookies or URL rewriting to maintain session affinity. The cookie or rewritten URL contains session affinity information that enables the Web server to properly route a session back to the same server for each request.


See Also

Managing HTTP sessions