Session Tracking with Servlets 

Purpose

You can use HTTP sessions and the corresponding API in your servlets to be able to keep track of client actions performed within your web application. Ability to preserve client state over several request-response cycles is a crucial feature of most real business applications. Furthermore, using additional techniques, you can make the state persistent, thus providing your applications with a degree of fault tolerance.

You can use both cookies, or URL rewriting to exchange session related information between the client and the server. Cookies are used by default, but in cases when client browser does not accept or support cookies, URL rewriting is the alternative.

Process Flow

The session tracking works the following way:

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       1.      When the very first request from a client comes to the AS Java, a session object is created and associated with that client. The object lives on the server for its lifetime. Servlets use it to store information about that particular client. The AS Java’s Web Container generates a unique session ID and sends it with the response to the client using JSESSIONID cookie, or URL rewriting.

       2.      On each consequent request from the client, the Web Container looks up the HttpSession object that is associated with the request using the session ID.

       3.      The servlet retrieves the session-related information that is stored on the server-side.

       4.      If client performs any actions that need to be stored, the servlet associates the corresponding information with the session.

       5.      After the session is completed (or timed out due to inactivity) the session object is removed from the server.