Support CompletableFuture in @MessageMapping handler methods

Issue: SPR-12207

spring-messaging/src/main/java/org/springframework/messaging/handler/invocation/CompletableFutureReturnValueHandler.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2002-2015 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.messaging.handler.invocation;
+
+import java.util.concurrent.CompletableFuture;
+
+import org.springframework.core.MethodParameter;
+import org.springframework.lang.UsesJava8;
+import org.springframework.util.concurrent.CompletableToListenableFutureAdapter;
+import org.springframework.util.concurrent.ListenableFuture;
+
+/**
+ * An {@link AsyncHandlerMethodReturnValueHandler} for {@link CompletableFuture} return type handling.
+ *
+ * @author Sebastien Deleuze
+ * @since 4.2
+ */
+@UsesJava8
+public class CompletableFutureReturnValueHandler extends AbstractAsyncReturnValueHandler {
+
+	@Override
+	public boolean supportsReturnType(MethodParameter returnType) {
+		return CompletableFuture.class.isAssignableFrom(returnType.getParameterType());
+	}
+
+	@Override
+	@SuppressWarnings("unchecked")
+	public ListenableFuture<?> toListenableFuture(Object returnValue, MethodParameter returnType) {
+		return new CompletableToListenableFutureAdapter<Object>((CompletableFuture<Object>)returnValue);
+	}
+
+}

spring-messaging/src/main/java/org/springframework/messaging/simp/annotation/support/SimpAnnotationMethodMessageHandler.java

@@ -50,6 +50,7 @@ import org.springframework.messaging.handler.annotation.support.MessageMethodArg
 import org.springframework.messaging.handler.annotation.support.PayloadArgumentResolver;
 import org.springframework.messaging.handler.invocation.AbstractExceptionHandlerMethodResolver;
 import org.springframework.messaging.handler.invocation.AbstractMethodMessageHandler;
+import org.springframework.messaging.handler.invocation.CompletableFutureReturnValueHandler;
 import org.springframework.messaging.handler.invocation.HandlerMethodArgumentResolver;
 import org.springframework.messaging.handler.invocation.HandlerMethodReturnValueHandler;
 import org.springframework.messaging.handler.invocation.ListenableFutureReturnValueHandler;
@@ -83,6 +84,10 @@ import org.springframework.validation.Validator;
 public class SimpAnnotationMethodMessageHandler extends AbstractMethodMessageHandler<SimpMessageMappingInfo>
 		implements SmartLifecycle {
 
+	private static final boolean completableFuturePresent = ClassUtils.isPresent("java.util.concurrent.CompletableFuture",
+			SimpAnnotationMethodMessageHandler.class.getClassLoader());
+
+
 	private final SubscribableChannel clientInboundChannel;
 
 	private final SimpMessageSendingOperations clientMessagingTemplate;
@@ -318,6 +323,10 @@ public class SimpAnnotationMethodMessageHandler extends AbstractMethodMessageHan
 		// Single-purpose return value types
 		ListenableFutureReturnValueHandler lfh = new ListenableFutureReturnValueHandler();
 		handlers.add(lfh);
+		if (completableFuturePresent) {
+			CompletableFutureReturnValueHandler cfh = new CompletableFutureReturnValueHandler();
+			handlers.add(cfh);
+		}
 
 		// Annotation-based return value types
 		SendToMethodReturnValueHandler sth = new SendToMethodReturnValueHandler(this.brokerTemplate, true);