Burlando o @Async do Spring

It is common when building applications using Spring, to use the @EnableAsync annotation to enable asynchronous executions and with the help of @Async over methods easily make them asynchronous.

@Async has basically two usage rules:

• the annotated method must be public
• the method invoker cannot be from the same class

In the example below, there will be no compilation problems, but the method (despite being annotated with @Async) will not execute as desired.

@Slf4j
@Service
@RequiredArgsConstructor
public class HelloService {

    public String get() {
        log.info("Chegou!");
        print();

        return "Ola!";
    }

    @Async
    @SneakyThrows
    public void print() {
        Thread.sleep(Duration.ofSeconds(5));

        log.info("Burlado!");
    }
}

And it is very common for us to wish that, because it is the responsibility of the class, the block of code that must be executed asynchronously remains in it. How to solve?

Simple!

We just need to create another class that helps, for example:

@Service
public class AsyncService {

    @Async
    public void run(final Runnable runnable) {
        runnable.run();
    }

    @Async
    public <O> O run(final Supplier<O> supplier) {
        return supplier.get();
    }
}

We do dependency injection of this bean where asynchronous execution is desirable and on top of that, we can make the method private.

@Slf4j
@Service
@RequiredArgsConstructor
public class HelloService {

    private final AsyncService asyncService;

    public String get() {
        log.info("Chegou!");

        asyncService.run(this::print);

        return "Ola!";
    }

    @SneakyThrows
    private void print() {
        Thread.sleep(Duration.ofSeconds(5));

        log.info("Burlado!");
    }
}

This small example demonstrates the application of several concepts and resources: Inversion of Control, Dependency Injection, SOLID, Design Pattern, Functional Interfaces.

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