how may session attributes i have maintained in my whole application
You can get the names of all session attributes in a particular session using HttpSession.getAttributeNames() method.
In many times in my code now i want to remove all those session at the time of Log off
Do you want to remove all the sessions or session attributes?? Generally when a user logs off, the session is ended using HttpSession.invalidate(), this removes all the attributes from the session and kills the session itself...