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Using other reactive programming libraries#

You may need to integrate libraries exposing an API using other reactive programming libraries such as RX Java or Reactor. Mutiny has a built-in conversion mechanism to ease that integration.

Picking the right dependency#

You need to add another dependency to access the converters. Each artifact contains the converters for a specific reactive library. Pick the right one and add it to your project:

<!-- Mutiny <-> Reactor -->
<dependency>
    <groupId>io.smallrye.reactive</groupId>
    <artifactId>mutiny-reactor</artifactId>
    <version>1.7.0</version>
</dependency>

<!-- Mutiny <-> RX Java 3 -->
<dependency>
    <groupId>io.smallrye.reactive</groupId>
    <artifactId>mutiny-rxjava3</artifactId>
    <version>1.7.0</version>
</dependency>

Integration with Project Reactor#

Project Reactor is a popular reactive programming library. It offers two types: Mono and Flux, both implementing Reactive Stream Publisher.

To use the Reactor <-> Mutiny converter, add the following imports to your class:

import io.smallrye.mutiny.converters.multi.MultiReactorConverters;
import io.smallrye.mutiny.converters.uni.UniReactorConverters;

Converting a Flux or a Mono into a Multi#

Both Flux and Mono implement Publisher. As a result, we can use the Reactive Streams interoperability to convert instances from Flux<T> and Mono<T> to Multi<T>:

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Multi<T> multiFromFlux = Multi.createFrom().publisher(flux);
Multi<T> multiFromMono = Multi.createFrom().publisher(mono);

Converting a Flux or a Mono into a Uni#

As you can create Uni from a Publisher, the same approach can be used to create Uni instances:

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Uni<T> uniFromFlux = Uni.createFrom().publisher(flux);
Uni<T> uniFromMono = Uni.createFrom().publisher(mono);

When a Flux or Mono sends the completion event without having emitted any item, the resulting Uni emits null.

When converting a Flux to Uni, the resulting Uni emits the first item. After that emission, it cancels the subscription to the Flux.

Converting a Multi into a Flux or Mono#

Converting a Multi into a Flux or a Mono uses the Reactive Streams interoperability:

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Flux<T> fluxFromMulti = Flux.from(multi);
Mono<T> monoFromMulti = Mono.from(multi);

Converting a Uni into a Flux or Mono#

Converting a Uni into a Flux or a Mono requires a converter, as Uni does not implement Reactive Streams.

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Flux<T> fluxFromUni = uni.convert().with(UniReactorConverters.toFlux());
Mono<T> monoFromUni = uni.convert().with(UniReactorConverters.toMono());

If the Uni emits null, it sends the completion event.

Using converter instead of Reactive Streams#

While Reactive Streams interoperability is convenient, Mutiny also provides converters to create Flux and Mono from Uni and Multi:

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Mono<String> mono = uni.convert().with(UniReactorConverters.toMono());
Flux<String> flux = uni.convert().with(UniReactorConverters.toFlux());

Mono<String> mono = multi.convert().with(MultiReactorConverters.toMono());
Flux<String> flux = multi.convert().with(MultiReactorConverters.toFlux());

Integration with RX Java 3#

RxJava is another popular reactive programming library. It offers 5 types: Completable (no item), Single (one item), Maybe (0 or 1 item), Observable (multiple items), Flowable (multiple items, implements Reactive Stream Publisher).

To use the RxJava <-> Mutiny converters, add the following imports to your class:

import io.smallrye.mutiny.converters.multi.MultiRx3Converters;
import io.smallrye.mutiny.converters.uni.UniRx3Converters;

Converting an Observable or a Flowable into a Multi#

Both Observable and Flowable are item streams. However, Observable does not implement Publisher and so does not have back-pressure support.

To create Multi from an Observable, you need a specific converter:

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Multi<T> multiFromObservable = Multi.createFrom()
        .converter(MultiRx3Converters.fromObservable(), observable);

Converting a Flowable is easier, as it’s a Publisher:

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Multi<T> multiFromFlowable = Multi.createFrom().publisher(flowable);

Converting a Completable, Single or Maybe into a Multi#

To create a Multi from a Completable, Single or Maybe you need specific converters, as none of these types implement Reactive Streams.

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Multi<Void> multiFromCompletable = Multi.createFrom()
        .converter(MultiRx3Converters.fromCompletable(), completable);
Multi<T> multiFromSingle = Multi.createFrom()
        .converter(MultiRx3Converters.fromSingle(), single);
Multi<T> multiFromMaybe = Multi.createFrom()
        .converter(MultiRx3Converters.fromMaybe(), maybe);
Multi<T> multiFromEmptyMaybe = Multi.createFrom()
        .converter(MultiRx3Converters.fromMaybe(), emptyMaybe);
  • Creating a Multi from a Completable always produces a Multi<Void> that only emits the completion or failure event.
  • Creating a Multi from a Single produces a Multi. That Multi emits the item and then completes it.
  • Creating a Multi from a Maybe produces a Multi. That Multi emits the item (if any) and then completes it. If the Maybe is empty, then the created Multi emits the completion event.

When a Completable, Single, or Maybe emits a failure, then the resulting Multi emits that failure.

Converting an Observable or a Flowable into a Uni#

To create a Uni from an Observable, you need to use a specific converter:

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Uni<T> uniFromObservable = Uni.createFrom().converter(
        UniRx3Converters.fromObservable(), observable);

The creation from a Flowable can be done using the Reactive Streams interoperability:

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Uni<T> uniFromFlowable = Uni.createFrom().publisher(flowable);

In both cases, it cancels the subscription to the Flowable or Observable after receiving the first item. If the Flowable or Observable completes without items, the Uni emits a null item.

Converting a Completable, Single or Maybe into a Uni#

To create a Uni from a Completable, Single, or Maybe, you need to use a specific converter:

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Uni<Void> multiFromCompletable = Uni.createFrom()
        .converter(UniRx3Converters.fromCompletable(), completable);
Uni<T> multiFromSingle = Uni.createFrom()
        .converter(UniRx3Converters.fromSingle(), single);
Uni<T> multiFromMaybe = Uni.createFrom()
        .converter(UniRx3Converters.fromMaybe(), maybe);
Uni<T> multiFromEmptyMaybe = Uni.createFrom()
        .converter(UniRx3Converters.fromMaybe(), emptyMaybe);

Converting a Completable to a Uni always produces a Uni<Void>, that emits either null once the Completable completes or the failure if it fails. The Maybe to Uni conversion emits a null item if the Maybe completes without an item.

Converting a Multi into a RX Java objects#

The conversion from a Multi to the various RX Java objects is done using converters:

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Completable completable = multi.convert()
        .with(MultiRx3Converters.toCompletable());
Single<Optional<T>> single = multi.convert()
        .with(MultiRx3Converters.toSingle());
Single<T> single2 = multi.convert()
        .with(MultiRx3Converters
                .toSingle().onEmptyThrow(() -> new Exception("D'oh!")));
Maybe<T> maybe = multi.convert()
        .with(MultiRx3Converters.toMaybe());
Observable<T> observable = multi.convert()
        .with(MultiRx3Converters.toObservable());
Flowable<T> flowable = multi.convert()
        .with(MultiRx3Converters.toFlowable());

The creation of a Completable from a Multi discards all the items emitted by the Multi. It only forwards the completion or failure event.

Converting a Multi into a Single returns a Single<Optional<T>>, as the Multi may complete without items. You can also produce a Single<T> and emit a failure event if the Multi completes without items. You can configure the thrown exception using onEmptyThrow.

Tip

You can also create a Flowable from a Multi using: Flowable.fromPublisher(multi).

Converting a Uni into a RX Java type#

Similarly to the conversion from a Multi into an RX Type, converting a Uni requires a converter:

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Completable completable = uni.convert().with(UniRx3Converters.toCompletable());
Single<Optional<T>> single = uni.convert().with(UniRx3Converters.toSingle());
Single<T> single2 = uni.convert().with(UniRx3Converters.toSingle().failOnNull());
Maybe<T> maybe = uni.convert().with(UniRx3Converters.toMaybe());
Observable<T> observable = uni.convert().with(UniRx3Converters.toObservable());
Flowable<T> flowable = uni.convert().with(UniRx3Converters.toFlowable());

The creation of a Completable from a Uni discards the item and sends the completion signal after emission.

Converting a Uni into a Single returns a Single<Optional<T>>, as the Uni may emit null. You can also produce a Single<T> and emits a failure event if the Uni sends null. Configure the failure to forward using failOnNull.

The creation of a Maybe, Flowable, or an Observable from a Uni produces an empty Maybe, Flowable, or Observable if the Uni emits null. For Flowable and Observable, if the Uni emits a non-null item, that item is emitted, followed immediately by the completion signal.