code: private synchronized HttpSubSession getSubSession() {
  		HttpSession backingSession = super.getSession();
  		Map<Integer, HttpSubSession> subsessions = (Map<Integer, HttpSubSession>) backingSession
  				.getAttribute(SESSION_MAP_KEY);
  
  		HttpSubSession subsession = subsessions.get(sessionId);
  		subsession.setLastAccessedTime(System.currentTimeMillis());
  
  		return subsession;
  	}
docs: Retrieves the subsession for this request. If there is no existing subsession, a new one is created.
  
  @return the subsession for this request.