Writing imperative code in Project Reactor

Question

I have a class with the following two methods.

public class Test1 {
    public Mono<String> blah1() {
        Mono<String> blah = Mono.just("blah1");
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println("blah1 done");
        return blah;
    }
    
    public Mono<String> blah2() {
        Mono<String> blah = Mono.just("blah2");
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println("blah2 done");
        return blah;
    }
}

I have the following JUnit:

@Test
public void blah1Test() {
    Flux<Tuple2<String, String>> s = Flux.zip(test1.blah1(), test1.blah2());    
}

My result is as follows:

blah1 done
blah2 done

I expect blah2 to finish before blah1. Thus I believe this is processing blocking instead of non blocking. What do I need to do to have the output switch to blah2 done then blah1 done? Basically why are these not processing in parallel?

Thanks in advance for your time!

Answer 1

Both sleep and println are executed outside the reactive pipeline. Therefore, both blah1() and blah2() behave like regular, non-reactive methods.

Try this:

public Mono<String> blah1() {
    System.out.println("blah1 start");
    return Mono.just("blah1")
        .delayElement(Duration.ofMillis(5000))
        .doOnNext(e -> System.out.println("blah1 done"));
}

public Mono<String> blah2() {
    System.out.println("blah2 start");
    return Mono.just("blah2")
        .delayElement(Duration.ofMillis(1000))
        .doOnNext(e -> System.out.println("blah2 done"));
}

Here, we have the expected result because printing takes place within the reactive pipeline.

Output:

blah1  start 
blah2 start 
blah2 done
blah1 done