title: Auto Log Off once the session expires
body: <p>Our application logs off after 30 min and gets redirected to login page,i am specifying session timeout in web.xml and using a requestProcessor for redirecting.I want to show to the user a message saying your session got expired once the session expires,how can i do that.Auto log off ?
  I would like to prompt the error message on the page"The session is timeout, please login again" . Then how could I detect the session is timeout? will any methods trigger automatically?</p>