code: public synchronized ID addOnline(final USER user, final ID sessionId, final SESSION session)
  	{
  		sessionIdToSession.put(sessionId, session);
  		return super.addOnline(user, sessionId);
  	}
docs: Adds the user online.
  
  @param user
  the user
  @param sessionId
  the session id
  @param session
  the session object
  @return the session id