Automatic Session Timeout

Recently I was given an assignment to provide a solution to the automatic session timeout. The requirement was that the end user needs to be alerted of the session timeout and inform him to recreate his session to proceed with the application.

I know that all J2EE application servers provides a session timeout value, but the timeout on the server side will not be informed back to the end user. So, I thought of creating a Poll action which receives an ajax request from the browser. The session timeout is got from the database and when the server's last access time reaches more than the seesion time the Poll action explicitly invalidates the session.