@Override
 public void discardTimedOut() {
   for (String name : request.getSession(true).getAttributeNames(SESSION_KEY_PREFIX)) {
     ScreenState screen = (ScreenState) getHttpSession().getAttribute(name);
     if (screen.isTimedOut()) {
       LOG.trace("Screen timed out: " + screen.getId());
       discard(screen.getId());
     }
   }
 }