Controlling Session Timeout in JSP

Hii there...
I want to put some kind of Alert Popup on JSP Page that occurs when there is 10 minute left in session time out...let's say i have specified 30 min as session timeout in web.xml file.If user doesn't do anything for 20 mins ..then i want to pop up a alert (for example -- You are not doing anything so the session will expire in 10 mins )..How to do that ???
[ September 13, 2005: Message edited by: Bear Bibeault ]

Bhavik,
When the page loads, start a timer in javascript. After 20 minutes, have it pop up an alert.

i don't want to put JUST an alert after 20 mins..i want to check and make sure no activity is done in last 20 mins and if that's the case pop an alert...

A filter that intercepts every request, and updates a timestamp in a session scoped bean would provide the server side to this solution.
Have your javascript function call a servlet that checks this bean after 20 minutes.

Of course the act of checking is, in itself activity.
It wouldn't be hard, though to exclude checks to to that servlet when updating the timestamp.

use session.getCreationTime() which gives the time the session was created. Add the max. session time to it and subtract 10mins from it and take that time as x. when this time x is reached give the pop-up.

i want to check and make sure no activity is done

What consititutes 'activity'? Moving the mouse? Client-side events?

What you're trying to do makes no sense to me since any non-client activity will extend the session timeout.