Compatibility with Flow-based SmallRye Mutiny 2 at runtime

Includes simple Flow.Publisher bridge without Reactor.

Closes gh-31000

spring-core/src/main/java/org/springframework/core/ReactiveAdapterRegistry.java

@@ -16,6 +16,7 @@
 
 package org.springframework.core;
 
+import java.lang.reflect.Method;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
@@ -24,9 +25,9 @@ import java.util.concurrent.CompletionStage;
 import java.util.concurrent.Flow;
 import java.util.function.Function;
 
-import kotlinx.coroutines.CompletableDeferredKt;
-import kotlinx.coroutines.Deferred;
 import org.reactivestreams.Publisher;
+import org.reactivestreams.Subscriber;
+import org.reactivestreams.Subscription;
 import reactor.adapter.JdkFlowAdapter;
 import reactor.blockhound.BlockHound;
 import reactor.blockhound.integration.BlockHoundIntegration;
@@ -36,15 +37,18 @@ import reactor.core.publisher.Mono;
 import org.springframework.lang.Nullable;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.ConcurrentReferenceHashMap;
+import org.springframework.util.ReflectionUtils;
 
 /**
- * A registry of adapters to adapt Reactive Streams {@link Publisher} to/from
- * various async/reactive types such as {@code CompletableFuture}, RxJava
- * {@code Flowable}, and others.
+ * A registry of adapters to adapt Reactive Streams {@link Publisher} to/from various
+ * async/reactive types such as {@code CompletableFuture}, RxJava {@code Flowable}, etc.
+ * This is designed to complement Spring's Reactor {@code Mono}/{@code Flux} support while
+ * also being usable without Reactor, e.g. just for {@code org.reactivestreams} bridging.
  *
- * <p>By default, depending on classpath availability, adapters are registered
- * for Reactor, RxJava 3, {@link CompletableFuture}, {@code Flow.Publisher},
- * and Kotlin Coroutines' {@code Deferred} and {@code Flow}.
+ * <p>By default, depending on classpath availability, adapters are registered for Reactor
+ * (including {@code CompletableFuture} and {@code Flow.Publisher} adapters), RxJava 3,
+ * Kotlin Coroutines' {@code Deferred} (bridged via Reactor) and SmallRye Mutiny 1.x/2.x.
+ * If Reactor is not present, a simple {@code Flow.Publisher} bridge will be registered.
  *
  * @author Rossen Stoyanchev
  * @author Sebastien Deleuze
@@ -79,6 +83,7 @@ public class ReactiveAdapterRegistry {
 	 * Create a registry and auto-register default adapters.
 	 * @see #getSharedInstance()
 	 */
+	@SuppressWarnings("unchecked")
 	public ReactiveAdapterRegistry() {
 		// Reactor
 		if (reactorPresent) {
@@ -99,6 +104,14 @@ public class ReactiveAdapterRegistry {
 		if (mutinyPresent) {
 			new MutinyRegistrar().registerAdapters(this);
 		}
+
+		// Simple Flow.Publisher bridge if Reactor is not present
+		if (!reactorPresent) {
+			registerReactiveType(
+					ReactiveTypeDescriptor.multiValue(Flow.Publisher.class, () -> PublisherToRS.EMPTY_FLOW),
+					source -> new PublisherToRS<>((Flow.Publisher<Object>) source),
+					source -> new PublisherToFlow<>((Publisher<Object>) source));
+		}
 	}
 
 
@@ -304,9 +317,9 @@ public class ReactiveAdapterRegistry {
 		@SuppressWarnings("KotlinInternalInJava")
 		void registerAdapters(ReactiveAdapterRegistry registry) {
 			registry.registerReactiveType(
-					ReactiveTypeDescriptor.singleOptionalValue(Deferred.class,
-							() -> CompletableDeferredKt.CompletableDeferred(null)),
-					source -> CoroutinesUtils.deferredToMono((Deferred<?>) source),
+					ReactiveTypeDescriptor.singleOptionalValue(kotlinx.coroutines.Deferred.class,
+							() -> kotlinx.coroutines.CompletableDeferredKt.CompletableDeferred(null)),
+					source -> CoroutinesUtils.deferredToMono((kotlinx.coroutines.Deferred<?>) source),
 					source -> CoroutinesUtils.monoToDeferred(Mono.from(source)));
 
 			registry.registerReactiveType(
@@ -319,20 +332,182 @@ public class ReactiveAdapterRegistry {
 
 	private static class MutinyRegistrar {
 
-		void registerAdapters(ReactiveAdapterRegistry registry) {
-			registry.registerReactiveType(
-					ReactiveTypeDescriptor.singleOptionalValue(
-							io.smallrye.mutiny.Uni.class,
-							() -> io.smallrye.mutiny.Uni.createFrom().nothing()),
-					uni -> ((io.smallrye.mutiny.Uni<?>) uni).convert().toPublisher(),
-					publisher -> io.smallrye.mutiny.Uni.createFrom().publisher(publisher));
+		private static final Method uniToPublisher = ClassUtils.getMethod(io.smallrye.mutiny.groups.UniConvert.class, "toPublisher");
 
-			registry.registerReactiveType(
-					ReactiveTypeDescriptor.multiValue(
-							io.smallrye.mutiny.Multi.class,
-							() -> io.smallrye.mutiny.Multi.createFrom().empty()),
-					multi -> (io.smallrye.mutiny.Multi<?>) multi,
-					publisher -> io.smallrye.mutiny.Multi.createFrom().publisher(publisher));
+		@SuppressWarnings("unchecked")
+		void registerAdapters(ReactiveAdapterRegistry registry) {
+			ReactiveTypeDescriptor uniDesc = ReactiveTypeDescriptor.singleOptionalValue(
+					io.smallrye.mutiny.Uni.class,
+					() -> io.smallrye.mutiny.Uni.createFrom().nothing());
+			ReactiveTypeDescriptor multiDesc = ReactiveTypeDescriptor.multiValue(
+					io.smallrye.mutiny.Multi.class,
+					() -> io.smallrye.mutiny.Multi.createFrom().empty());
+
+			if (Flow.Publisher.class.isAssignableFrom(uniToPublisher.getReturnType())) {
+				// Mutiny 2 based on Flow.Publisher
+				Method uniPublisher = ClassUtils.getMethod(io.smallrye.mutiny.groups.UniCreate.class, "publisher", Flow.Publisher.class);
+				Method multiPublisher = ClassUtils.getMethod(io.smallrye.mutiny.groups.MultiCreate.class, "publisher", Flow.Publisher.class);
+				registry.registerReactiveType(uniDesc,
+						uni -> new PublisherToRS<>((Flow.Publisher<Object>) ReflectionUtils.invokeMethod(uniToPublisher, ((io.smallrye.mutiny.Uni<?>) uni).convert())),
+						publisher -> ReflectionUtils.invokeMethod(uniPublisher, io.smallrye.mutiny.Uni.createFrom(), new PublisherToFlow<>(publisher)));
+				registry.registerReactiveType(multiDesc,
+						multi -> new PublisherToRS<>((Flow.Publisher<Object>) multi),
+						publisher -> ReflectionUtils.invokeMethod(multiPublisher, io.smallrye.mutiny.Multi.createFrom(), new PublisherToFlow<>(publisher)));
+			}
+			else {
+				// Mutiny 1 based on Reactive Streams
+				registry.registerReactiveType(uniDesc,
+						uni -> ((io.smallrye.mutiny.Uni<?>) uni).convert().toPublisher(),
+						publisher -> io.smallrye.mutiny.Uni.createFrom().publisher(publisher));
+				registry.registerReactiveType(multiDesc,
+						multi -> (io.smallrye.mutiny.Multi<?>) multi,
+						publisher -> io.smallrye.mutiny.Multi.createFrom().publisher(publisher));
+			}
+		}
+	}
+
+
+	private static class PublisherToFlow<T> implements Flow.Publisher<T> {
+
+		private static final Flow.Subscription EMPTY_SUBSCRIPTION = new Flow.Subscription() {
+			@Override
+			public void request(long n) {
+			}
+			@Override
+			public void cancel() {
+			}
+		};
+
+		@Nullable
+		private final Publisher<T> publisher;
+
+		public PublisherToFlow(@Nullable Publisher<T> publisher) {
+			this.publisher = publisher;
+		}
+
+		@Override
+		public void subscribe(Flow.Subscriber<? super T> subscriber) {
+			if (this.publisher != null) {
+				this.publisher.subscribe(new SubscriberToFlow<>(subscriber));
+			}
+			else {
+				subscriber.onSubscribe(EMPTY_SUBSCRIPTION);
+				subscriber.onComplete();
+			}
+		}
+	}
+
+
+	private static class PublisherToRS<T> implements Publisher<T> {
+
+		private static final Flow.Publisher<Object> EMPTY_FLOW = new PublisherToFlow<>(null);
+
+		private final Flow.Publisher<T> publisher;
+
+		@SuppressWarnings("unchecked")
+		public PublisherToRS(@Nullable Flow.Publisher<T> publisher) {
+			this.publisher = (publisher != null ? publisher : (Flow.Publisher<T>) EMPTY_FLOW);
+		}
+
+		@Override
+		public void subscribe(Subscriber<? super T> subscriber) {
+			this.publisher.subscribe(new SubscriberToRS<>(subscriber));
+		}
+	}
+
+
+	private static class SubscriberToFlow<T> implements Subscriber<T>, Flow.Subscription {
+
+		private final Flow.Subscriber<? super T> subscriber;
+
+		@Nullable
+		private Subscription subscription;
+
+		public SubscriberToFlow(Flow.Subscriber<? super T> subscriber) {
+			this.subscriber = subscriber;
+		}
+
+		@Override
+		public void onSubscribe(Subscription subscription) {
+			this.subscription = subscription;
+			this.subscriber.onSubscribe(this);
+		}
+
+		@Override
+		public void onNext(T o) {
+			this.subscriber.onNext(o);
+		}
+
+		@Override
+		public void onError(Throwable t) {
+			this.subscriber.onError(t);
+		}
+
+		@Override
+		public void onComplete() {
+			this.subscriber.onComplete();
+		}
+
+		@Override
+		public void request(long n) {
+			if (this.subscription != null) {
+				this.subscription.request(n);
+			}
+		}
+
+		@Override
+		public void cancel() {
+			if (this.subscription != null) {
+				this.subscription.cancel();
+			}
+		}
+	}
+
+
+	private static class SubscriberToRS<T> implements Flow.Subscriber<T>, Subscription {
+
+		private final Subscriber<? super T> subscriber;
+
+		@Nullable
+		private Flow.Subscription subscription;
+
+		public SubscriberToRS(Subscriber<? super T> subscriber) {
+			this.subscriber = subscriber;
+		}
+
+		@Override
+		public void onSubscribe(Flow.Subscription subscription) {
+			this.subscription = subscription;
+			this.subscriber.onSubscribe(this);
+		}
+
+		@Override
+		public void onNext(T o) {
+			this.subscriber.onNext(o);
+		}
+
+		@Override
+		public void onError(Throwable throwable) {
+			this.subscriber.onError(throwable);
+		}
+
+		@Override
+		public void onComplete() {
+			this.subscriber.onComplete();
+		}
+
+		@Override
+		public void request(long n) {
+			if (this.subscription != null) {
+				this.subscription.request(n);
+			}
+		}
+
+		@Override
+		public void cancel() {
+			if (this.subscription != null) {
+				this.subscription.cancel();
+			}
 		}
 	}
 

spring-core/src/test/java/org/springframework/core/ReactiveAdapterRegistryTests.java

@@ -20,6 +20,7 @@ import java.time.Duration;
 import java.util.Arrays;
 import java.util.List;
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Flow;
 
 import io.smallrye.mutiny.Multi;
 import io.smallrye.mutiny.Uni;
@@ -27,6 +28,7 @@ import kotlinx.coroutines.Deferred;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.reactivestreams.Publisher;
+import reactor.adapter.JdkFlowAdapter;
 import reactor.core.CoreSubscriber;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
@@ -112,6 +114,16 @@ class ReactiveAdapterRegistryTests {
 			assertThat(((Mono<Integer>) target).block(ONE_SECOND)).isEqualTo(Integer.valueOf(1));
 		}
 
+		@Test
+		void toFlowPublisher() {
+			List<Integer> sequence = Arrays.asList(1, 2, 3);
+			Publisher<Integer> source = io.reactivex.rxjava3.core.Flowable.fromIterable(sequence);
+			Object target = getAdapter(Flow.Publisher.class).fromPublisher(source);
+			assertThat(target).isInstanceOf(Flow.Publisher.class);
+			assertThat(JdkFlowAdapter.flowPublisherToFlux((Flow.Publisher<Integer>) target)
+					.collectList().block(ONE_SECOND)).isEqualTo(sequence);
+		}
+
 		@Test
 		void toCompletableFuture() throws Exception {
 			Publisher<Integer> source = Flux.fromArray(new Integer[] {1, 2, 3});