How to use Spring WebClient to make multiple calls simultaneously?

Question

I want to execute 3 calls simultaneously and process the results once they're all done.

I know this can be achieved using AsyncRestTemplate as it is mentioned here How to use AsyncRestTemplate to make multiple calls simultaneously?

However, AsyncRestTemplate is deprecated in favor of WebClient. I have to use Spring MVC in the project but interested if I can use a WebClient just to execute simultaneous calls. Can someone advise how this should be done properly with WebClient?

Answer 1

Assuming a WebClient wrapper (like in reference doc):

@Service
public class MyService {

    private final WebClient webClient;

    public MyService(WebClient.Builder webClientBuilder) {
        this.webClient = webClientBuilder.baseUrl("http://example.org").build();
    }

    public Mono<Details> someRestCall(String name) {
        return this.webClient.get().url("/{name}/details", name)
                        .retrieve().bodyToMono(Details.class);
    }

}

..., you could invoke it asynchronously via:

// ... 
  @Autowired
  MyService myService
  // ...

   Mono<Details> foo = myService.someRestCall("foo");
   Mono<Details> bar = myService.someRestCall("bar");
   Mono<Details> baz = myService.someRestCall("baz");

   // ..and use the results (thx to: [2] & [3]!):

   // Subscribes sequentially:

   // System.out.println("=== Flux.concat(foo, bar, baz) ===");
   // Flux.concat(foo, bar, baz).subscribe(System.out::print);

   // System.out.println("\n=== combine the value of foo then bar then baz ===");
   // foo.concatWith(bar).concatWith(baz).subscribe(System.out::print);

   // ----------------------------------------------------------------------
   // Subscribe eagerly (& simultaneously):
   System.out.println("\n=== Flux.merge(foo, bar, baz) ===");
   Flux.merge(foo, bar, baz).subscribe(System.out::print);

[2] [3]

Thanks, Welcome & Kind Regards,