Using Spring4 AsyncRestTemplate in a method which uses an @Async annotation

Question

I am using the Spring4 AsyncRestTemplate to make calls to an External REST API service.

The method below is from a Spring @Service class. The AsyncRestTemplate is autowired from a Spring @Bean.

In the method, I register callbacks on the ListenableFuture response from the REST API call.

I don't use the returned ListenableFuture except for unit tests. The callbacks will handle the actual actions I want to take based on request success or failure.

ExternalServiceImpl.class

public ListenableFuture<ResponseEntity<ResponseBody>> makeExternalCall(RequestBody requestBody) {

            HttpEntity<RequestBody> request = new HttpEntity<>(RequestBody, getDefaultHeaders());

            ListenableFuture<ResponseEntity<ResponseBody>> responseEntity = asyncRestTemplate.exchange(serviceUri.toUriString(), HttpMethod.POST, request, ResponseBody.class);

            responseEntity.addCallback(
                    (onSuccess) -> System.out.println("Success"), 
                    (onFailure) -> onFailure.printStackTrace()
            );

            return responseEntity;
    }

I plan on using the @EnableAsync annotation and setting up a ThreadPoolTaskExecutor as well as adding an @async annotation to the method in a manner similar to the procedure described here: Spring Asynchronous Methods

Questions

Is this redundant? Is there an additional benefit to scaling when making the method async even though I'm using an AsyncRestTemplate?
Is there anything considered best practice that I'm missing in
implementing this pattern?
Is there anything to watch out for?

Pete Pete · Accepted Answer · 2016-10-14T00:45:32

@Async doesn't actually do anything until you add the @EnableAsync annotation to your application. When that happens, any code calling your makeExternalCall method will immediately return, and spring will look for a TaskExecutor bean to run the whole method asynchronously (rather than just your asyncRestTemplate service being the only async part of your code currently).

More info on the spring website: http://docs.spring.io/spring/docs/current/spring-framework-reference/html/scheduling.html

Using Spring4 AsyncRestTemplate in a method which uses an @Async annotation

1 Answers