AsyncExecutionInterceptor supports Java 8's CompletableFuture as a return type

Issue: SPR-13128

spring-aop/src/main/java/org/springframework/aop/interceptor/AsyncExecutionInterceptor.java

@@ -18,9 +18,12 @@ package org.springframework.aop.interceptor;
 
 import java.lang.reflect.Method;
 import java.util.concurrent.Callable;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Future;
+import java.util.function.Supplier;
 
 import org.aopalliance.intercept.MethodInterceptor;
 import org.aopalliance.intercept.MethodInvocation;
@@ -30,6 +33,7 @@ import org.springframework.core.BridgeMethodResolver;
 import org.springframework.core.Ordered;
 import org.springframework.core.task.AsyncListenableTaskExecutor;
 import org.springframework.core.task.AsyncTaskExecutor;
+import org.springframework.lang.UsesJava8;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.concurrent.ListenableFuture;
 
@@ -68,6 +72,11 @@ import org.springframework.util.concurrent.ListenableFuture;
 public class AsyncExecutionInterceptor extends AsyncExecutionAspectSupport
 		implements MethodInterceptor, Ordered {
 
+	// Java 8's CompletableFuture type present?
+	private static final boolean completableFuturePresent = ClassUtils.isPresent(
+			"java.util.concurrent.CompletableFuture", AsyncExecutionInterceptor.class.getClassLoader());
+
+
 	/**
 	 * Create a new {@code AsyncExecutionInterceptor}.
 	 * @param defaultExecutor the {@link Executor} (typically a Spring {@link AsyncTaskExecutor}
@@ -124,6 +133,12 @@ public class AsyncExecutionInterceptor extends AsyncExecutionAspectSupport
 		};
 
 		Class<?> returnType = invocation.getMethod().getReturnType();
+		if (completableFuturePresent) {
+			Future<Object> result = CompletableFutureDelegate.processCompletableFuture(returnType, task, executor);
+			if (result != null) {
+				return result;
+			}
+		}
 		if (ListenableFuture.class.isAssignableFrom(returnType)) {
 			return ((AsyncListenableTaskExecutor) executor).submitListenable(task);
 		}
@@ -154,4 +169,29 @@ public class AsyncExecutionInterceptor extends AsyncExecutionAspectSupport
 		return Ordered.HIGHEST_PRECEDENCE;
 	}
 
+
+	/**
+	 * Inner class to avoid a hard dependency on Java 8.
+	 */
+	@UsesJava8
+	private static class CompletableFutureDelegate {
+
+		public static <T> Future<T> processCompletableFuture(Class<?> returnType, final Callable<T> task, Executor executor) {
+			if (!CompletableFuture.class.isAssignableFrom(returnType)) {
+				return null;
+			}
+			return CompletableFuture.supplyAsync(new Supplier<T>() {
+				@Override
+				public T get() {
+					try {
+						return task.call();
+					}
+					catch (Throwable ex) {
+						throw new CompletionException(ex);
+					}
+				}
+			}, executor);
+		}
+	}
+
 }