public Interface WebSocketHandler

A server WebSocketHandler is mapped to requests with SimpleUrlHandlerMapping and WebSocketHandlerAdapter. A client WebSocketHandler is passed to the WebSocketClient execute method.

Use session.receive() to compose on the inbound message stream, and session.send(publisher) for the outbound message stream. Below is an example, combined flow to process inbound and to send outbound messages:

 class ExampleHandler implements WebSocketHandler {

 	@Override
 	public Mono<Void> handle(WebSocketSession session) {

 		Flux<WebSocketMessage> output = session.receive()
			.doOnNext(message -> {
 				// ...
 			})
 			.concatMap(message -> {
 				// ...
 			})
 			.map(value -> session.textMessage("Echo " + value));

 		return session.send(output);
 	}
 }
 

If processing inbound and sending outbound messages are independent streams, they can be joined together with the "zip" operator:

 class ExampleHandler implements WebSocketHandler {

 	@Override
 	public Mono<Void> handle(WebSocketSession session) {

 		Mono<Void> input = session.receive()
			.doOnNext(message -> {
 				// ...
 			})
 			.concatMap(message -> {
 				// ...
 			})
 			.then();

		Flux<String> source = ... ;
 		Mono<Void> output = session.send(source.map(session::textMessage));

 		return Mono.zip(input, output).then();
 	}
 }
 

A WebSocketHandler must compose the inbound and outbound streams into a unified flow and return a Mono<Void> that reflects the completion of that flow. That means there is no need to check if the connection is open, since Reactive Streams signals will terminate activity. The inbound stream receives a completion/error signal, and the outbound stream receives a cancellation signal.