Spring WebFlux (Flux): how to publish dynamically

问题:

I am new to Reactive programming and Spring WebFlux. I want to make my App 1 publish Server Sent event through Flux and my App 2 listen on it continuously.

I want Flux publish on-demand (e.g. when something happens). All the example I found is to use Flux.interval to periodically publish event, and there seems no way to append/modify the content in Flux once it is created.

How can I achieve my goal? Or I am totally wrong conceptually.

回答1:

Publish "dynamically" using FluxProcessor and FluxSink

One of the techniques to supply data manually to the Flux is using FluxProcessor#sink method as in the following example

@SpringBootApplication @RestController public class DemoApplication {      final FluxProcessor processor;     final FluxSink sink;     final AtomicLong counter;      public static void main(String[] args) {         SpringApplication.run(DemoApplication.class, args);      }      public DemoApplication() {         this.processor = DirectProcessor.create().serialize();         this.sink = processor.sink();         this.counter = new AtomicLong();     }      @GetMapping("/send")     public void test() {         sink.next("Hello World #" + counter.getAndIncrement());     }      @RequestMapping(produces = MediaType.TEXT_EVENT_STREAM_VALUE)     public Flux<ServerSentEvent> sse() {         return processor.map(e -> ServerSentEvent.builder(e).build());     } }

Here, I created DirectProcessor in order to support multiple subscribers, that will listen to the data stream. Also, I provided additional FluxProcessor#serialize which provide safe support for multiproducer (invocation from different threads without violation of Reactive Streams spec rules, especially rule 1.3). Finally, by calling "http://localhost:8080/send" we will see the message Hello World #1 (of course, only in case if you connected to the "http://localhost:8080" previously)

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