title: jsp filter, get page name
body: <p>I want to create a jsp login filter. </p>
  
  <p>The filter should:</p>
  
  <ul>
  <li>intercept requests to any page; verify whether the request is part of a logged-session</li>
  <li>if the session is not logged, redirect the client to a login page</li>
  <li>if the requested page is the login page, don't redirect, otherwise it will loop</li>
  </ul>
  
  <p>thanks in advance</p>