spring - How to limit the request/second with WebClient?

Question

I'm using a WebClient object to send Http Post request to a server. It's sending a huge amount of requests quite rapidly (there is about 4000 messages in a QueueChannel). The problem is... it seems the server can't respond fast enough... so I'm getting a lot of server error 500 and connexion closed prematurely.

Is there a way to limit the number of request per seconds ? Or limit the number of threads it's using ?

EDIT :

The Message endpoint processe message in a QueueChannel :

@MessageEndpoint
public class CustomServiceActivator {

    private static final Logger logger = LogManager.getLogger();

    @Autowired
    IHttpService httpService;

    @ServiceActivator(
            inputChannel = "outputFilterChannel",
            outputChannel = "outputHttpServiceChannel",
            poller = @Poller( fixedDelay = "1000" )
    )
    public void processMessage(Data data) {
        httpService.push(data);
        try {
            Thread.sleep(20);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

}

The WebClient service class :

@Service
public class HttpService implements IHttpService {

    private static final String URL = "http://www.blabla.com/log";

    private static final Logger logger = LogManager.getLogger();

    @Autowired
    WebClient webClient;

    @Override
    public void push(Data data) {
        String body = constructString(data);
        Mono<ResponseEntity<Response>> res = webClient.post()
                .uri(URL + getLogType(data))
                .contentLength(body.length())
                .contentType(MediaType.APPLICATION_JSON)
                .syncBody(body)
                .exchange()
                .flatMap(response -> response.toEntity(Response.class));

        res.subscribe(new Consumer<ResponseEntity<Response>>() { ... });
    }
}

Answer 1

Question Limiting rate of requests with Reactor provides two answrers (one in comment)

zipWith another flux that acts as rate limiter

.zipWith(Flux.interval(Duration.of(1, ChronoUnit.SECONDS)))

just delay each web request

use delayElements function

edit: answer below is valid for blocking RestTemplate but do not really fit well into reactive pattern.

WebClient does not have ability to limit request, but you could easily add this feature using composition.

You may throttle your client externally using RateLimiter from Guava/ (https://google.github.io/guava/releases/19.0/api/docs/index.html?com/google/common/util/concurrent/RateLimiter.html)

In this tutorial http://www.baeldung.com/guava-rate-limiter you will find how to use Rate limiter in blocking way, or with timeouts.

I would decorate all calls that need to be throttled in separate class that

1. limits number of calls per second
2. performs actual web call using WebClient