Path variables in Spring WebSockets @SendTo mapping

java, sockjs, spring, stomp, websocket

Solution

Even though `@MessageMapping` supports placeholders, they are not exposed / resolved in `@SendTo` destinations. Currently, there's no way to define dynamic destinations with the `@SendTo` annotation (see issue SPR-12170). You could use the `SimpMessagingTemplate` for the time being (that's how it works internally anyway). Here's how you would do it:

@MessageMapping("/fleet/{fleetId}/driver/{driverId}")
public void simple(@DestinationVariable String fleetId, @DestinationVariable String driverId) {
    simpMessagingTemplate.convertAndSend("/topic/fleet/" + fleetId, new Simple(fleetId, driverId));
}

In your code, the destination '/topic/fleet/{fleetId}' is treated as a literal, that's the reason why subscribing to it works, just because you are sending to the exact same destination.

If you just want to send some initial user specific data, you could return it directly in the subscription:

@SubscribeMapping("/fleet/{fleetId}/driver/{driverId}")
public Simple simple(@DestinationVariable String fleetId, @DestinationVariable String driverId) {
    return new Simple(fleetId, driverId);
}

Update: In Spring 4.2, destination variable placeholders are supported it's now possible to do something like:

@MessageMapping("/fleet/{fleetId}/driver/{driverId}")
@SendTo("/topic/fleet/{fleetId}")
public Simple simple(@DestinationVariable String fleetId, @DestinationVariable String driverId) {
    return new Simple(fleetId, driverId);
}

Problem

I have, what I think to be, a very simple Spring WebSocket application. However, I'm trying to use path variables for the subscription as well as the message mapping. I've posted a paraphrased example below. I would expect the `@SendTo` annotation to return back to the subscribers based on their `fleetId`. ie, a `POST` to `/fleet/MyFleet/driver/MyDriver` should notify subscribers of `/fleet/MyFleet`, but I'm not seeing this behavior. It's worth noting that subscribing to literal `/fleet/{fleetId}` works. Is this intended? Am I missing some piece of configuration? Or is this just not how it works? I'm not very familiar with WebSockets or this Spring project yet, so thanks in advance. Controller.java ``` ... @MessageMapping("/fleet/{fleetId}/driver/{driverId}") @SendTo("/topic/fleet/{fleetId}") public Simple simple(@DestinationVariable String fleetId, @DestinationVariable String driverId) { return new Simple(fleetId, driverId); } ... ``` WebSocketConfig.java ``` @Configuration @EnableWebSocketMessageBroker public class WebSocketConfig extends AbstractWebSocketMessageBrokerConfigurer { @Override public void configureMessageBroker(MessageBrokerRegistry config) { config.enableSimpleBroker("/topic"); config.setApplicationDestinationPrefixes("/live"); } @Override public void registerStompEndpoints(StompEndpointRegistry registry) { registry.addEndpoint("/fleet").withSockJS(); } } ``` index.html ``` var socket = new SockJS('/fleet'); var stompClient = Stomp.over(socket); stompClient.connect({}, function(frame) { // Doesn't Work stompClient.subscribe('/topic/fleet/MyFleet', function(greeting) { // Works stompClient.subscribe('/topic/fleet/{fleetId}', function(greeting) { // Do some stuff }); }); ``` Send Sample ``` stompClient.send("/live/fleet/MyFleet/driver/MyDriver", {}, JSON.stringify({ // Some simple content })); ```

Original source