i want to know what will happen if didnt configure this element in the web.xml is that container will provide any default values for this, also i want know the different behavior when this element is not set in web.xml
but iam able to deploy the application without this element in the web.xml with jboss 4.0
Setting session timeout through the deployment descriptor should work - it sets the default session timeout for the web app. Calling session.setMaxInactiveInterval() sets the timeout for the particular session it is called on, and overrides the default. Be aware of the unit difference, too - the deployment descriptor version uses minutes, and session.setMaxInactiveInterval() uses seconds.
sets the default session timeout to 60 minutes.
sets the session timeout to 600 seconds - 10 minutes - for the specific session it's called on.
This should work in Tomcat or Glassfish or any other Java web server - it's part of the spec.