Spring WebSocket @SendToSession: send message to specific session

Question

Is it possible to send a message to specific session?

I have an unauthenticated websocket between clients and a Spring servlet. I need to send an unsolicited message

Answer 1

No need to create specific destinations, it's already done out of the box as of Spring 4.1 (see SPR-11309).

Given users subscribe to a /user/queue/something queue, you can send a message to a single session with:

As stated in the SimpMessageSendingOperations Javadoc, since your user name is actually a sessionId, you MUST set that as a header as well otherwise the DefaultUserDestinationResolver won't be able to route the message and will drop it.

SimpMessageHeaderAccessor headerAccessor = SimpMessageHeaderAccessor
    .create(SimpMessageType.MESSAGE);
headerAccessor.setSessionId(sessionId);
headerAccessor.setLeaveMutable(true);

messagingTemplate.convertAndSendToUser(sessionId,"/queue/something", payload, 
    headerAccessor.getMessageHeaders());

You don't need users to be authenticated for this.

Answer 2

You need to simply add the session id in

• Server Side

  convertAndSendToUser(sessionId,apiName,responseObject);

• Client Side

  $stomp.subscribe('/user/+sessionId+'/apiName',handler);

Note:
Dont forget to add '/user' in your end point in server side.

Answer 3

It is very complicated and in my opinion, isn't worth it. You need to create a subscription for every user (even unauthenticated ones) by their session id.

Let's say that every user subscribes to a unique queue only for him:

stompClient.subscribe('/session/specific' + uuid, handler);

On the server, before the user subscribes you will need to notify and send a message for the specific session and save to a map:

    @MessageMapping("/putAnonymousSession/{sessionId}")
    public void start(@DestinationVariable sessionId) throws Exception {
        anonymousUserSession.put(key, sessionId);
    }

After that, when you want to send message to the user you will need to:

messagingTemplate.convertAndSend("/session/specific" + key); 

But I don't really know what you are trying to do and how you will find the specific session (who is anonymous).