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Annotated Controllers

Applications can use annotated @Controller classes to handle messages from clients. Such classes can declare @MessageMapping, @SubscribeMapping, and @ExceptionHandler methods, as described in the following topics:

@MessageMapping

You can use @MessageMapping to annotate methods that route messages based on their destination. It is supported at the method level as well as at the type level. At the type level, @MessageMapping is used to express shared mappings across all methods in a controller.

By default, the mapping values are Ant-style path patterns (for example /thing*, /thing/**), including support for template variables (for example, /thing/{id}). The values can be referenced through @DestinationVariable method arguments. Applications can also switch to a dot-separated destination convention for mappings, as explained in Dots as Separators.

Supported Method Arguments

The following table describes the method arguments:

Method argument Description

Message

For access to the complete message.

MessageHeaders

For access to the headers within the Message.

MessageHeaderAccessor, SimpMessageHeaderAccessor, and StompHeaderAccessor

For access to the headers through typed accessor methods.

@Payload

For access to the payload of the message, converted (for example, from JSON) by a configured MessageConverter.

The presence of this annotation is not required since it is, by default, assumed if no other argument is matched.

You can annotate payload arguments with @jakarta.validation.Valid or Spring’s @Validated, to have the payload arguments be automatically validated.

@Header

For access to a specific header value — along with type conversion using an org.springframework.core.convert.converter.Converter, if necessary.

@Headers

For access to all headers in the message. This argument must be assignable to java.util.Map.

@DestinationVariable

For access to template variables extracted from the message destination. Values are converted to the declared method argument type as necessary.

java.security.Principal

Reflects the user logged in at the time of the WebSocket HTTP handshake.

Return Values

By default, the return value from a @MessageMapping method is serialized to a payload through a matching MessageConverter and sent as a Message to the brokerChannel, from where it is broadcast to subscribers. The destination of the outbound message is the same as that of the inbound message but prefixed with /topic.

You can use the @SendTo and @SendToUser annotations to customize the destination of the output message. @SendTo is used to customize the target destination or to specify multiple destinations. @SendToUser is used to direct the output message to only the user associated with the input message. See User Destinations.

You can use both @SendTo and @SendToUser at the same time on the same method, and both are supported at the class level, in which case they act as a default for methods in the class. However, keep in mind that any method-level @SendTo or @SendToUser annotations override any such annotations at the class level.

Messages can be handled asynchronously and a @MessageMapping method can return ListenableFuture, CompletableFuture, or CompletionStage.

Note that @SendTo and @SendToUser are merely a convenience that amounts to using the SimpMessagingTemplate to send messages. If necessary, for more advanced scenarios, @MessageMapping methods can fall back on using the SimpMessagingTemplate directly. This can be done instead of, or possibly in addition to, returning a value. See Sending Messages.

@SubscribeMapping

@SubscribeMapping is similar to @MessageMapping but narrows the mapping to subscription messages only. It supports the same method arguments as @MessageMapping. However for the return value, by default, a message is sent directly to the client (through clientOutboundChannel, in response to the subscription) and not to the broker (through brokerChannel, as a broadcast to matching subscriptions). Adding @SendTo or @SendToUser overrides this behavior and sends to the broker instead.

When is this useful? Assume that the broker is mapped to /topic and /queue, while application controllers are mapped to /app. In this setup, the broker stores all subscriptions to /topic and /queue that are intended for repeated broadcasts, and there is no need for the application to get involved. A client could also subscribe to some /app destination, and a controller could return a value in response to that subscription without involving the broker without storing or using the subscription again (effectively a one-time request-reply exchange). One use case for this is populating a UI with initial data on startup.

When is this not useful? Do not try to map broker and controllers to the same destination prefix unless you want both to independently process messages, including subscriptions, for some reason. Inbound messages are handled in parallel. There are no guarantees whether a broker or a controller processes a given message first. If the goal is to be notified when a subscription is stored and ready for broadcasts, a client should ask for a receipt if the server supports it (simple broker does not). For example, with the Java STOMP client, you could do the following to add a receipt:

@Autowired
private TaskScheduler messageBrokerTaskScheduler;

// During initialization..
stompClient.setTaskScheduler(this.messageBrokerTaskScheduler);

// When subscribing..
StompHeaders headers = new StompHeaders();
headers.setDestination("/topic/...");
headers.setReceipt("r1");
FrameHandler handler = ...;
stompSession.subscribe(headers, handler).addReceiptTask(receiptHeaders -> {
	// Subscription ready...
});

A server side option is to register an ExecutorChannelInterceptor on the brokerChannel and implement the afterMessageHandled method that is invoked after messages, including subscriptions, have been handled.

@MessageExceptionHandler

An application can use @MessageExceptionHandler methods to handle exceptions from @MessageMapping methods. You can declare exceptions in the annotation itself or through a method argument if you want to get access to the exception instance. The following example declares an exception through a method argument:

@Controller
public class MyController {

	// ...

	@MessageExceptionHandler
	public ApplicationError handleException(MyException exception) {
		// ...
		return appError;
	}
}

@MessageExceptionHandler methods support flexible method signatures and support the same method argument types and return values as @MessageMapping methods.

Typically, @MessageExceptionHandler methods apply within the @Controller class (or class hierarchy) in which they are declared. If you want such methods to apply more globally (across controllers), you can declare them in a class marked with @ControllerAdvice. This is comparable to the similar support available in Spring MVC.