Microservice return response first and then process the request

Question

I am working on a solution for which i am trying to create a microservice which returns response immediately and then processes the request.

I am trying to use Java 8 and Spring for this.

Answer 1

This can be achieved in several ways.

In order to return a result from the current thread (a controller in this case) while still doing some long-running operation, you will need another thread.

• Use Executor directly.

A controller:

@Controller
public class AsyncController {

    private AsyncService asyncService;

    @Autowired
    public void setAsyncService(AsyncService asyncService) {
        this.asyncService = asyncService;
    }

    private ResponseEntity asyncMethod(@RequestBody Object request) {
        asyncService.process(new MyLongRunningRunnable());

        // returns immediately
        return ResponseEntity.ok("ok");
    }
}

And a service:

@Service
public class AsyncService {
    private ExecutorService executorService;

    @PostConstruct
    private void create() {
        executorService = Executors.newSingleThreadExecutor();
    }

    public void process(Runnable operation) {
        // no result operation
        executorService.submit(operation);
    }


    @PreDestroy
    private void destroy() {
        executorService.shutdown();
    }
}

More details can be found here https://docs.oracle.com/javase/tutorial/essential/concurrency/runthread.html

• Another way is to use Spring built-in async capabilities

You can simply annotate a method with @Async, having void or Future return type.

If you still want to supply your own executor, you may implement AsyncConfigurer interface in your spring configuration bean. This approach also requires @EnableAsync annotation.

@Configuration
@EnableAsync
public class AsyncConfiguration implements AsyncConfigurer {

    @Override
    public Executor getAsyncExecutor() {
        return Executors.newSingleThreadExecutor();
    }

}

More on this topic https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/scheduling/annotation/Async.html