code: @Post("/obj/future")
      @ProducesJson
      public CompletionStage<Response> json4(@RequestObject Request request,
                                             ServiceRequestContext ctx) {
          final CompletableFuture<Response> future = new CompletableFuture<>();
          ctx.blockingTaskExecutor()
             .submit(() -> future.complete(new Response(Response.SUCCESS, request.name())));
          return future;
      }
docs: Returns a {@link CompletionStage} object. The {@link JacksonResponseConverterFunction} will
  be executed after the future is completed with the {@link Response} object.
  
  <p>Note that the {@link ServiceRequestContext} of the request is also automatically injected. See
  <a href="https://line.github.io/armeria/server-annotated-service.html#other-classes-automatically-injected">
  Other classes automatically injected</a> for more information.