How to call several http requests in parallel(with retry functionality) and await when all of them are finish?

Question

For now my code looks like this:

   List<Mono<ResponseEntity<String>>> response = queue.stream()
            .map(req-> webClient
                    .post()
                    .bodyValue(req)
                    .retrieve()
                    .toEntity(String.class)
            )
            .collect(Collectors.toList());

How could I await the moment when all responses will be accepted ?

If some of requests are failed I would like to retry only them.

How could I achieve it?

Answer 1

Rather than going with ExecutorService suggested by another answer, I'd recommend using the capabilities of Mono and Flux which provides a more idiomatic solution:

Mono<List<String>> response = Flux.fromIterable(queue)
                                  .flatMap(this::callHttp)
                                  .collectList();

private Mono<String> callHttp(String req)
{
    return webClient
            .post()
            .syncBody(req)
            .retrieve()
            .bodyToMono(String.class)
            .retry(3); // retries failed requests at most 3 times
}