sample ReactiveController in spring, for stackoverflow question

ReactiveController.java

@Controller
@Slf4j
public class ReactiveController {
    record SomeDTO(String name, String address) {
    }

    private final Sinks.Many<SomeDTO> eventSink = Sinks.many().replay().latest();

    @RequestMapping(path = "/sse", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
    public Flux<ServerSentEvent<SomeDTO>> sse() {
        final AtomicLong counter = new AtomicLong(0);
        return eventSink.asFlux()
                .map(e -> ServerSentEvent.builder(e)
                        .id(counter.incrementAndGet() + "")
                        //.event(e.getClass().getName())
                        .build());
    }

    // note, when you want this to work in production, ensure, that http request is not being cached on its way, using POST method for example.
    @ResponseStatus(HttpStatus.OK)
    @ResponseBody
    @GetMapping(path = "/sendSomething", produces = MediaType.TEXT_PLAIN_VALUE)
    public String sendSomething() {
        this.eventSink.emitNext(
                new SomeDTO("name", "address"),
                (signalType, emitResult) -> {
                    log.warn("Some event is being not send to all subscribers. It will vanish...");
                    // returning false, to not retry emitting given data again.
                    return false;
                }
        );
        return "Have a look at /sse endpoint (using \"curl http://localhost/sse\" for example), to see events in realtime.";
    }
}