Limiting rate of requests with Reactor

问题

I'm using project reactor to load data from a web service using rest. This is done in parallel with multiple threads. I'm starting to hit rate limits on the web service, so I would like to send at most 10 requests per second to avoid getting these errors. How would I do that using reactor?

Using zipWith(Mono.delayMillis(100))? Or is there some better way?

Thank you

回答1:

You can use delayElements instead of the whole zipwith.

回答2:

The code below will do a GET on https://www.google.com/ at a rate of 10 requests per second. You'll have to do additional changes in order to support the situation where your server is not able to process in 1s all your 10 requests; you could just skip sending requests when those asked at previous second are still processed by your server.

@Test
void parallelHttpRequests() {
    // this is just for limiting the test running period otherwise you don't need it
    int COUNT = 2;

    // use whatever (blocking) http client you desire;
    // when using e.g. WebClient (Spring, non blocking client)
    // the example will slightly change for no longer use
    // subscribeOn(Schedulers.elastic())
    RestTemplate client = new RestTemplate();

    var exit = new AtomicBoolean(false);
    var lock = new ReentrantLock();
    var condition = lock.newCondition();

    MessageFormat message = new MessageFormat("#batch: {0}, #req: {1}, resultLength: {2}");
    Flux.interval(Duration.ofSeconds(1L))
            .take(COUNT) // this is just for limiting the test running period otherwise you don't need it
            .doOnNext(batch -> debug("#batch", batch)) // just for debugging
            .flatMap(batch -> Flux.range(1, 10) // 10 requests per 1 second
                            .flatMap(i -> Mono.fromSupplier(() ->
                                    client.getForEntity("https://www.google.com/", String.class).getBody()) // your request goes here (1 of 10)
                                    .map(s -> message.format(new Object[]{batch, i, s.length()})) // here the request's result will be the output of message.format(...)
                                    .doOnSubscribe(s -> debug("doOnSubscribe: #batch = " + batch + ", i = " + i)) // just for debugging
                                    .subscribeOn(Schedulers.elastic()) // one I/O thread per request
                            )
            )
            .subscribe(
                    s -> debug("received", s) // do something with the above request's result
                    e -> {
                        debug("error", e.getMessage());
                        signalAll(exit, condition, lock);
                    },
                    () -> {
                        debug("done");
                        signalAll(exit, condition, lock);
                    }
            );

    await(exit, condition, lock);
}

private void await(AtomicBoolean exit, Condition condition, Lock lock) {
    lock.lock();
    while (!exit.get()) {
        try {
            condition.await();
        } catch (InterruptedException e) {
            // maybe spurious wakeup
            e.printStackTrace();
        }
    }
    lock.unlock();
    debug("exit");
}

private void signalAll(AtomicBoolean exit, Condition condition, Lock lock) {
    exit.set(true);
    try {
        lock.lock();
        condition.signalAll();
    } finally {
        lock.unlock();
    }
}

来源：https://stackoverflow.com/questions/43799891/limiting-rate-of-requests-with-reactor

标签

java

project-reactor