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How chain indefinite amount of flatMap operators in Reactor?


How chain indefinite amount of flatMap operators in Reactor?

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How chain indefinite amount of flatMap operators in Reactor?
Tag : development , By : markku
Date : January 11 2021, 03:32 PM

this will help This seems difficult because you're streaming your baseState, then trying to do an arbitrary number of flatMap() calls on that. There's nothing inherently wrong with using a loop to achieve this, but I like to avoid that unless absolutely necessary, as it breaks the natural reactive flow of the code.
If you instead iterate and reduce the policies into a single policy, then the flatMap() call becomes trivial:
Flux.fromIterable(policies)
        .reduce((p1,p2) -> s -> p1.apply(s).flatMap(p2::apply))
        .flatMap(p -> p.apply(baseState))
        .subscribe();
interface Policy {
    Mono<State> apply(State currentState);

    public static Policy combine(Policy p1, Policy p2) {
        return s -> p1.apply(s).flatMap(p2::apply);
    }
}
Flux.fromIterable(policies)
        .reduce(Policy::combine)
        .flatMap(p -> p.apply(baseState))
        .subscribe();
interface Policy {
    Mono<String> apply(String currentState);

    public static Policy combine(Policy p1, Policy p2) {
        return s -> p1.apply(s).flatMap(p2::apply);
    }
}

public static void main(String[] args) {
    List<Policy> policies = new ArrayList<>();
    policies.add(x -> Mono.just("blah " + x));
    policies.add(x -> Mono.just("foo " + x));

    String baseState = "bar";
    Flux.fromIterable(policies)
            .reduce(Policy::combine)
            .flatMap(p -> p.apply(baseState))
            .subscribe(System.out::println); //Prints "foo blah bar"

}

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Reactor compose vs flatMap


Tag : java , By : desmiserables
Date : March 29 2020, 07:55 AM
around this issue An excellent explanation by Dan Lew:
The difference is that compose() is a higher level abstraction: it operates on the entire stream, not individually emitted items. In more specific terms:

map vs flatMap in reactor


Tag : java , By : Sebastián Ucedo
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further map is for synchronous, non-blocking, 1-to-1 transformations flatMap is for asynchronous (non-blocking) 1-to-N transformations
The difference is visible in the method signature:

How to use Context with flatMap() in Reactor?


Tag : java , By : besn
Date : March 29 2020, 07:55 AM
will help you Chain your Publishers and may the Context be with you
In the case, you connected all your Publishers (and this includes connections within the flatMap/concatMap and similar operators) you will have Context correctly propagated among the whole stream runtime.
public class TestFlatMap {
    public static void main(final String ...args) {
        final Flux<String> greetings = Flux.just("Hubert", "Sharon")
                                           .flatMap(TestFlatMap::nameToGreeting)
                                           .subscriberContext(context ->
                                                   Context.of("greetingWord", "Hello")  // context initialized
                                           );
        greetings.subscribe(System.out::println);
    }

    private static Mono<String> nameToGreeting(final String name) {
        return Mono.subscriberContext()
                   .filter(c -> c.hasKey("greetingWord"))
                   .map(c -> c.get("greetingWord"))
                   .flatMap(greetingWord -> Mono.just(greetingWord + " " + name + " " + "!!!"));// ALERT: we have Context here !!!
    }
}
public class TestFlatMap {
    public static void main(final String ...args) {
        final Flux<String> greetings = Flux.just("Hubert", "Sharon")
                                           .flatMap(TestFlatMap::nameToGreeting)
                                           .subscriberContext(context ->
                                                   Context.of("greetingWord", "Hello")  // context initialized
                                           );
        greetings.subscribe(System.out::println);
    }

    private static Mono<String> nameToGreeting(final String name) {
        return Mono.zip(
            Mono.subscriberContext()
                .filter(c -> c.hasKey("greetingWord"))
                .map(c -> c.get("greetingWord")), // ALERT: we have Context here !!!
            Mono.just(name),
            (greetingWord, receivedName) -> greetingWord + " " + receivedName + " " + "!!!"
        );
    }
}

Issue with use of project reactor's flatMap and switchIfEmpty operators


Tag : development , By : cjdavis
Date : March 29 2020, 07:55 AM
Does that help It's not to do with flatMap() or switchIfEmpty() directly - it's because you're trying to consume the same Mono twice:
Mono<User> userMono = serverRequest.bodyToMono(User.class);
return validateUser(userMono)
    .switchIfEmpty(saveUser(userMono))
    .single();

Backpressure with flatmap in io reactor


Tag : spring-boot , By : user123585
Date : March 29 2020, 07:55 AM
hop of those help? There is an overload of flatMap in which you can set the concurrency parameter (actually more of a parallelism factor) and the prefetch parameter (which defaults to 256). The last one is the amount the inner flux is requested on the first time, so you could set it to 1.
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