Add support for Deferred to ReactiveAdapterRegistry

See gh-19975

spring-core/spring-core.gradle

@@ -78,6 +78,8 @@ dependencies {
 	optional("io.reactivex:rxjava-reactive-streams:${rxjavaAdapterVersion}")
 	optional("io.reactivex.rxjava2:rxjava:${rxjava2Version}")
 	optional("io.netty:netty-buffer")
+	optional("org.jetbrains.kotlinx:kotlinx-coroutines-core:${coroutinesVersion}")
+	optional("org.jetbrains.kotlinx:kotlinx-coroutines-reactor:${coroutinesVersion}")
 	testCompile("io.projectreactor:reactor-test")
 	testCompile("org.apache.tomcat.embed:tomcat-embed-core:${tomcatVersion}")
 	testCompile("org.xmlunit:xmlunit-matchers:2.6.2")

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

@@ -40,8 +40,8 @@ import org.springframework.util.ReflectionUtils;
  * {@code Observable}, and others.
  *
  * <p>By default, depending on classpath availability, adapters are registered
- * for Reactor, RxJava 1, RxJava 2 types, {@link CompletableFuture}, and Java 9+
+ * for Reactor, RxJava 1, RxJava 2 types, {@link CompletableFuture}, Java 9+
- * Flow.Publisher.
+ * {@code Flow.Publisher} and Kotlin Coroutines {@code Deferred}.
  *
  * @author Rossen Stoyanchev
  * @author Sebastien Deleuze
@@ -90,6 +90,11 @@ public class ReactiveAdapterRegistry {
 		}
 		// If not present, do nothing for the time being...
 		// We can fall back on "reactive-streams-flow-bridge" (once released)
+
+		// Coroutines
+		if (ClassUtils.isPresent("kotlinx.coroutines.Deferred", classLoader)) {
+			CoroutinesRegistrarKt.registerAdapter(this);
+		}
 	}
 
 

spring-core/src/main/kotlin/org/springframework/core/CoroutinesRegistrar.kt

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2002-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.core
+
+import kotlinx.coroutines.Deferred
+import kotlinx.coroutines.GlobalScope
+import kotlinx.coroutines.async
+import kotlinx.coroutines.reactive.awaitFirstOrNull
+import kotlinx.coroutines.reactor.mono
+import reactor.core.publisher.toMono
+
+/**
+ * Register Reactive adapters for Coroutines types.
+ *
+ * @author Sebastien Deleuze
+ * @since 5.2
+ */
+internal fun registerAdapter(registry: ReactiveAdapterRegistry) {
+	registry.registerReactiveType(
+			ReactiveTypeDescriptor.singleOptionalValue(Deferred::class.java) { GlobalScope.async {} },
+			{ source -> GlobalScope.mono { (source as Deferred<*>).await() }},
+			{ source -> GlobalScope.async { source.toMono().awaitFirstOrNull() } }
+	)
+}

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,6 +23,7 @@ import java.util.concurrent.CompletableFuture;
 
 import io.reactivex.Flowable;
 import io.reactivex.Maybe;
+import kotlinx.coroutines.Deferred;
 import org.junit.Test;
 import org.reactivestreams.Publisher;
 import reactor.core.publisher.Flux;
@@ -68,6 +69,9 @@ public class ReactiveAdapterRegistryTests {
 		assertNotNull(getAdapter(io.reactivex.Single.class));
 		assertNotNull(getAdapter(Maybe.class));
 		assertNotNull(getAdapter(io.reactivex.Completable.class));
+
+		// Coroutines
+		assertNotNull(getAdapter(Deferred.class));
 	}
 
 	@Test

spring-core/src/test/kotlin/org/springframework/core/KotlinReactiveAdapterRegistryTests.kt

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2002-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.core
+
+import kotlinx.coroutines.Deferred
+import kotlinx.coroutines.GlobalScope
+import kotlinx.coroutines.async
+import kotlinx.coroutines.runBlocking
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
+import org.junit.Test
+import org.reactivestreams.Publisher
+import reactor.core.publisher.Mono
+import java.time.Duration
+import kotlin.reflect.KClass
+
+class KotlinReactiveAdapterRegistryTests {
+
+	private val registry = ReactiveAdapterRegistry.getSharedInstance()
+
+	@Test
+	fun deferredToPublisher() {
+		val source = GlobalScope.async { 1 }
+		val target: Publisher<Int> = getAdapter(Deferred::class).toPublisher(source)
+		assertTrue("Expected Mono Publisher: " + target.javaClass.name, target is Mono<*>)
+		assertEquals(1, (target as Mono<Int>).block(Duration.ofMillis(1000)))
+	}
+
+	@Test
+	fun publisherToDeferred() {
+		val source = Mono.just(1)
+		val target = getAdapter(Deferred::class).fromPublisher(source)
+		assertTrue(target is Deferred<*>)
+		assertEquals(1, runBlocking { (target as Deferred<*>).await() })
+
+	}
+
+	private fun getAdapter(reactiveType: KClass<*>): ReactiveAdapter {
+		return this.registry.getAdapter(reactiveType.java)!!
+	}
+}