SmallRye Mutiny

SmallRye Mutiny is a Reactive Streams implementation from Red Hat, supported by Spring WebFlux since Spring Framework 5.3.10. Developers who prefer Mutiny's event-driven API can use its types directly in controllers and repositories.

Flow API based

Earlier versions of SmallRye Mutiny implemented the Reactive Streams API; current versions use the JDK Flow API instead.

Add the dependency

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>io.smallrye.reactive</groupId>
            <artifactId>mutiny-bom</artifactId>
            <version>3.1.0</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

<dependencies>
    <dependency>
        <groupId>io.smallrye.reactive</groupId>
        <artifactId>mutiny</artifactId>
    </dependency>
    <!-- ... -->
</dependencies>

Core types

Mutiny's two core types map directly onto Reactor's:

Mutiny	Reactor	Emits
Uni<T>	Mono<T>	0..1 item (accepts null)
Multi<T>	Flux<T>	0..N items

Both implement the Reactive Streams Publisher contract, so Spring adapts them automatically wherever a Publisher is accepted.

Use Mutiny in a controller

Return Uni and Multi from controller methods exactly as you would return Mono and Flux:

@RestController
@RequestMapping(value = "/posts")
class PostController {

    private final PostRepository posts;

    public PostController(PostRepository posts) {
        this.posts = posts;
    }

    @GetMapping(value = "")
    public Multi<Post> all() {
        return this.posts.findAll();
    }

    @GetMapping(value = "/{id}")
    public Uni<Post> get(@PathVariable(value = "id") UUID id) {
        return this.posts.findById(id);
    }

    @PostMapping(value = "")
    public Uni<ResponseEntity<?>> create(@RequestBody Post post) {
        return this.posts.save(post).map(p -> ResponseEntity.created(URI.create("/posts/" + p.getId())).build());
    }
}

Spring handles the adaptation: a Multi is streamed like a Flux, a Uni resolves like a Mono, and Mutiny operators (onItem().transform(...), chain(...), and so on) work inside the methods.

You can explore the complete codes in spring-reactive-sample/smallrye-mutiny.