code: void sendSubscriptionEvent(String topic, int nb) {
  		Collection<Session> sessions = getSessionsForTopic(topic);
  		if (!sessions.isEmpty()) {
  			MessageToClient messageToClient = new MessageToClient();
  			messageToClient.setId(topic);
  			messageToClient.setType(MessageType.MESSAGE);
  			messageToClient.setResponse(nb);
  //			Collection<Session> sessionsClosed = new ArrayList<>(); // throws java.lang.StackOverflowError
  			for (Session session : sessions) {
  				if (session.isOpen()) {
  					session.getAsyncRemote().sendObject(messageToClient);
  //				} else {
  //					sessionsClosed.add(session);
  				}
  			}
  //			removeSessionsToTopic(sessionsClosed);
  		}
  	}
docs: Send subscription event to all client
  
  @param topic
  @param session