Deprecate ListenableFuture in favor of CompletableFuture

This commit deprecates ListenableFuture in favor of CompletableFuture.
ListenableFuture was introduced in Spring Framework 4.0, when
CompletableFuture was not yet available. Spring now requires JDK 17, so
having our own type no longer seems necessary.

Major changes in this commit include:
- Deprecation of ListenableFuture and related types
  (ListenableFutureCallback, SettableListenableFuture, etc.)
- Deprecation of AsyncListenableTaskExecutor in favor of default methods
  in AsyncTaskExecutor (submitCompletable).
- AsyncHandlerMethodReturnValueHandler now has toCompletableFuture
  instead of toListenableFuture.
- WebSocketClient now has execute methods, which do the same as
  doHandshake, but return CompletableFutures (cf. the reactive
  WebSocketClient).

All other changes
- add an overloaded method that takes a CompletableFuture parameter
  instead of ListenableFuture, and/or
- add a method with a 'Async' suffix that returns a CompletableFuture
  instead of a ListenableFuture (connectAsync, sendAsync).

Closes gh-27780

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

@@ -20,7 +20,6 @@
 import java.util.Map;
 import java.util.concurrent.Callable;
 import java.util.concurrent.CompletableFuture;
-import java.util.concurrent.CompletionException;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Future;
@@ -158,7 +157,6 @@ public void setBeanFactory(BeanFactory beanFactory) {
 
 	/**
 	 * Determine the specific executor to use when executing the given method.
-	 * <p>Should preferably return an {@link AsyncListenableTaskExecutor} implementation.
 	 * @return the executor to use (or {@code null}, but just if no default executor is available)
 	 */
 	@Nullable
@@ -176,8 +174,8 @@ protected AsyncTaskExecutor determineAsyncExecutor(Method method) {
 			if (targetExecutor == null) {
 				return null;
 			}
-			executor = (targetExecutor instanceof AsyncListenableTaskExecutor ?
-					(AsyncListenableTaskExecutor) targetExecutor : new TaskExecutorAdapter(targetExecutor));
+			executor = (targetExecutor instanceof AsyncTaskExecutor ?
+					(AsyncTaskExecutor) targetExecutor : new TaskExecutorAdapter(targetExecutor));
 			this.executors.put(method, executor);
 		}
 		return executor;
@@ -276,17 +274,11 @@ protected Executor getDefaultExecutor(@Nullable BeanFactory beanFactory) {
 	 * @param returnType the declared return type (potentially a {@link Future} variant)
 	 * @return the execution result (potentially a corresponding {@link Future} handle)
 	 */
+	@SuppressWarnings("deprecation")
 	@Nullable
 	protected Object doSubmit(Callable<Object> task, AsyncTaskExecutor executor, Class<?> returnType) {
 		if (CompletableFuture.class.isAssignableFrom(returnType)) {
-			return CompletableFuture.supplyAsync(() -> {
-				try {
-					return task.call();
-				}
-				catch (Throwable ex) {
-					throw new CompletionException(ex);
-				}
-			}, executor);
+			return executor.submitCompletable(task);
 		}
 		else if (ListenableFuture.class.isAssignableFrom(returnType)) {
 			return ((AsyncListenableTaskExecutor) executor).submitListenable(task);

spring-context-support/src/main/java/org/springframework/scheduling/quartz/SimpleThreadPoolTaskExecutor.java

@@ -47,6 +47,7 @@
  * @see org.springframework.core.task.TaskExecutor
  * @see SchedulerFactoryBean#setTaskExecutor
  */
+@SuppressWarnings("deprecation")
 public class SimpleThreadPoolTaskExecutor extends SimpleThreadPool
 		implements AsyncListenableTaskExecutor, SchedulingTaskExecutor, InitializingBean, DisposableBean {
 

spring-context/src/main/java/org/springframework/context/event/ApplicationListenerMethodAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -262,6 +262,7 @@ protected Object[] resolveArguments(ApplicationEvent event) {
 		return new Object[] {event};
 	}
 
+	@SuppressWarnings("deprecation")
 	protected void handleResult(Object result) {
 		if (reactiveStreamsPresent && new ReactiveResultHandler().subscribeToPublisher(result)) {
 			if (logger.isTraceEnabled()) {

spring-context/src/main/java/org/springframework/scheduling/annotation/AsyncResult.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -45,7 +45,9 @@
  * @see Async
  * @see #forValue(Object)
  * @see #forExecutionException(Throwable)
+ * @deprecated as of 6.0, in favor of {@link CompletableFuture}
  */
+@Deprecated
 public class AsyncResult<V> implements ListenableFuture<V> {
 
 	@Nullable

spring-context/src/main/java/org/springframework/scheduling/concurrent/ConcurrentTaskExecutor.java

@@ -62,6 +62,7 @@
  * @see DefaultManagedTaskExecutor
  * @see ThreadPoolTaskExecutor
  */
+@SuppressWarnings("deprecation")
 public class ConcurrentTaskExecutor implements AsyncListenableTaskExecutor, SchedulingTaskExecutor {
 
 	@Nullable

spring-context/src/main/java/org/springframework/scheduling/concurrent/ThreadPoolTaskExecutor.java

@@ -80,7 +80,7 @@
  * @see ThreadPoolExecutorFactoryBean
  * @see ConcurrentTaskExecutor
  */
-@SuppressWarnings("serial")
+@SuppressWarnings({"serial", "deprecation"})
 public class ThreadPoolTaskExecutor extends ExecutorConfigurationSupport
 		implements AsyncListenableTaskExecutor, SchedulingTaskExecutor {
 

spring-context/src/main/java/org/springframework/scheduling/concurrent/ThreadPoolTaskScheduler.java

@@ -59,7 +59,7 @@
  * @see #setThreadFactory
  * @see #setErrorHandler
  */
-@SuppressWarnings("serial")
+@SuppressWarnings({"serial", "deprecation"})
 public class ThreadPoolTaskScheduler extends ExecutorConfigurationSupport
 		implements AsyncListenableTaskExecutor, SchedulingTaskExecutor, TaskScheduler {
 

spring-context/src/test/java/org/springframework/scheduling/concurrent/AbstractSchedulingTaskExecutorTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -18,10 +18,13 @@
 
 import java.util.concurrent.Callable;
 import java.util.concurrent.CancellationException;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Future;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
 
@@ -33,6 +36,7 @@
 
 import org.springframework.beans.factory.DisposableBean;
 import org.springframework.core.task.AsyncListenableTaskExecutor;
+import org.springframework.lang.Nullable;
 import org.springframework.util.concurrent.ListenableFuture;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -135,6 +139,21 @@ void submitListenableRunnable() throws Exception {
 		assertThreadNamePrefix(task);
 	}
 
+	@Test
+	void submitCompletableRunnable() throws Exception {
+		TestTask task = new TestTask(this.testName, 1);
+		// Act
+		CompletableFuture<Void> future = executor.submitCompletable(task);
+		future.whenComplete(this::storeOutcome);
+		// Assert
+		Awaitility.await()
+					.atMost(1, TimeUnit.SECONDS)
+					.pollInterval(10, TimeUnit.MILLISECONDS)
+					.until(future::isDone);
+		assertThat(outcome).isNull();
+		assertThreadNamePrefix(task);
+	}
+
 	@Test
 	void submitFailingListenableRunnable() throws Exception {
 		TestTask task = new TestTask(this.testName, 0);
@@ -149,6 +168,20 @@ void submitFailingListenableRunnable() throws Exception {
 		assertThat(outcome.getClass()).isSameAs(RuntimeException.class);
 	}
 
+	@Test
+	void submitFailingCompletableRunnable() throws Exception {
+		TestTask task = new TestTask(this.testName, 0);
+		CompletableFuture<?> future = executor.submitCompletable(task);
+		future.whenComplete(this::storeOutcome);
+
+		Awaitility.await()
+					.dontCatchUncaughtExceptions()
+					.atMost(1, TimeUnit.SECONDS)
+					.pollInterval(10, TimeUnit.MILLISECONDS)
+					.until(() -> future.isDone() && outcome != null);
+		assertThat(outcome.getClass()).isSameAs(CompletionException.class);
+	}
+
 	@Test
 	void submitListenableRunnableWithGetAfterShutdown() throws Exception {
 		ListenableFuture<?> future1 = executor.submitListenable(new TestTask(this.testName, -1));
@@ -169,6 +202,26 @@ void submitListenableRunnableWithGetAfterShutdown() throws Exception {
 					future2.get(1000, TimeUnit.MILLISECONDS)));
 	}
 
+	@Test
+	void submitCompletableRunnableWithGetAfterShutdown() throws Exception {
+		CompletableFuture<?> future1 = executor.submitCompletable(new TestTask(this.testName, -1));
+		CompletableFuture<?> future2 = executor.submitCompletable(new TestTask(this.testName, -1));
+		shutdownExecutor();
+
+		try {
+			future1.get(1000, TimeUnit.MILLISECONDS);
+		}
+		catch (Exception ex) {
+			/* ignore */
+		}
+		Awaitility.await()
+			.atMost(4, TimeUnit.SECONDS)
+			.pollInterval(10, TimeUnit.MILLISECONDS)
+			.untilAsserted(() ->
+				assertThatExceptionOfType(TimeoutException.class).isThrownBy(() ->
+					future2.get(1000, TimeUnit.MILLISECONDS)));
+	}
+
 	@Test
 	void submitCallable() throws Exception {
 		TestCallable task = new TestCallable(this.testName, 1);
@@ -246,6 +299,57 @@ void submitListenableCallableWithGetAfterShutdown() throws Exception {
 		});
 	}
 
+	@Test
+	void submitCompletableCallable() throws Exception {
+		TestCallable task = new TestCallable(this.testName, 1);
+		// Act
+		CompletableFuture<String> future = this.executor.submitCompletable(task);
+		future.whenComplete(this::storeOutcome);
+		// Assert
+		Awaitility.await()
+					.atMost(1, TimeUnit.SECONDS)
+					.pollInterval(10, TimeUnit.MILLISECONDS)
+					.until(() -> future.isDone() && outcome != null);
+		assertThat(outcome.toString().substring(0, this.threadNamePrefix.length())).isEqualTo(this.threadNamePrefix);
+	}
+
+	@Test
+	void submitFailingCompletableCallable() throws Exception {
+		TestCallable task = new TestCallable(this.testName, 0);
+		// Act
+		CompletableFuture<String> future = this.executor.submitCompletable(task);
+		future.whenComplete(this::storeOutcome);
+		// Assert
+		Awaitility.await()
+					.dontCatchUncaughtExceptions()
+					.atMost(1, TimeUnit.SECONDS)
+					.pollInterval(10, TimeUnit.MILLISECONDS)
+					.until(() -> future.isDone() && outcome != null);
+		assertThat(outcome.getClass()).isSameAs(CompletionException.class);
+	}
+
+	@Test
+	void submitCompletableCallableWithGetAfterShutdown() throws Exception {
+		CompletableFuture<?> future1 = executor.submitCompletable(new TestCallable(this.testName, -1));
+		CompletableFuture<?> future2 = executor.submitCompletable(new TestCallable(this.testName, -1));
+		shutdownExecutor();
+		assertThatExceptionOfType(TimeoutException.class).isThrownBy(() -> {
+			future1.get(1000, TimeUnit.MILLISECONDS);
+			future2.get(1000, TimeUnit.MILLISECONDS);
+		});
+	}
+
+
+	private void storeOutcome(@Nullable Object o, @Nullable Throwable t) {
+		if (o != null) {
+			this.outcome = o;
+		}
+		else if (t != null) {
+			this.outcome = t;
+		}
+	}
+
+
 
 	protected void assertThreadNamePrefix(TestTask task) {
 		assertThat(task.lastThread.getName().substring(0, this.threadNamePrefix.length())).isEqualTo(this.threadNamePrefix);

spring-core/src/main/java/org/springframework/core/task/AsyncListenableTaskExecutor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -27,7 +27,11 @@
  * @author Arjen Poutsma
  * @since 4.0
  * @see ListenableFuture
+ * @deprecated as of 6.0, in favor of
+ * {@link AsyncTaskExecutor#submitCompletable(Runnable)} and
+ * {@link AsyncTaskExecutor#submitCompletable(Callable)}
  */
+@Deprecated
 public interface AsyncListenableTaskExecutor extends AsyncTaskExecutor {
 
 	/**
@@ -36,7 +40,9 @@ public interface AsyncListenableTaskExecutor extends AsyncTaskExecutor {
 	 * @param task the {@code Runnable} to execute (never {@code null})
 	 * @return a {@code ListenableFuture} representing pending completion of the task
 	 * @throws TaskRejectedException if the given task was not accepted
+	 * @deprecated in favor of {@link AsyncTaskExecutor#submitCompletable(Runnable)}
 	 */
+	@Deprecated
 	ListenableFuture<?> submitListenable(Runnable task);
 
 	/**
@@ -46,7 +52,9 @@ public interface AsyncListenableTaskExecutor extends AsyncTaskExecutor {
 	 * @param task the {@code Callable} to execute (never {@code null})
 	 * @return a {@code ListenableFuture} representing pending completion of the task
 	 * @throws TaskRejectedException if the given task was not accepted
+	 * @deprecated in favor of {@link AsyncTaskExecutor#submitCompletable(Callable)}
 	 */
+	@Deprecated
 	<T> ListenableFuture<T> submitListenable(Callable<T> task);
 
 }

spring-core/src/main/java/org/springframework/core/task/AsyncTaskExecutor.java

@@ -17,8 +17,11 @@
 package org.springframework.core.task;
 
 import java.util.concurrent.Callable;
+import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.Future;
 
+import org.springframework.util.concurrent.FutureUtils;
+
 /**
  * Extended interface for asynchronous {@link TaskExecutor} implementations,
  * offering support for {@link java.util.concurrent.Callable}.
@@ -91,4 +94,29 @@ public interface AsyncTaskExecutor extends TaskExecutor {
 	 */
 	<T> Future<T> submit(Callable<T> task);
 
+	/**
+	 * Submit a {@code Runnable} task for execution, receiving a {@code CompletableFuture}
+	 * representing that task. The Future will return a {@code null} result upon completion.
+	 * @param task the {@code Runnable} to execute (never {@code null})
+	 * @return a {@code CompletableFuture} representing pending completion of the task
+	 * @throws TaskRejectedException if the given task was not accepted
+	 * @since 6.0
+	 */
+	default CompletableFuture<Void> submitCompletable(Runnable task) {
+		return CompletableFuture.runAsync(task, this);
+	}
+
+	/**
+	 * Submit a {@code Callable} task for execution, receiving a {@code CompletableFuture}
+	 * representing that task. The Future will return the Callable's result upon
+	 * completion.
+	 * @param task the {@code Callable} to execute (never {@code null})
+	 * @return a {@code CompletableFuture} representing pending completion of the task
+	 * @throws TaskRejectedException if the given task was not accepted
+	 * @since 6.0
+	 */
+	default <T> CompletableFuture<T> submitCompletable(Callable<T> task) {
+		return FutureUtils.callAsync(task, this);
+	}
+
 }

spring-core/src/main/java/org/springframework/core/task/SimpleAsyncTaskExecutor.java

@@ -46,7 +46,7 @@
  * @see SyncTaskExecutor
  * @see org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor
  */
-@SuppressWarnings("serial")
+@SuppressWarnings({"serial", "deprecation"})
 public class SimpleAsyncTaskExecutor extends CustomizableThreadCreator
 		implements AsyncListenableTaskExecutor, Serializable {
 

spring-core/src/main/java/org/springframework/core/task/support/TaskExecutorAdapter.java

@@ -43,6 +43,7 @@
  * @see java.util.concurrent.ExecutorService
  * @see java.util.concurrent.Executors
  */
+@SuppressWarnings("deprecation")
 public class TaskExecutorAdapter implements AsyncListenableTaskExecutor {
 
 	private final Executor concurrentExecutor;

spring-core/src/main/java/org/springframework/util/concurrent/CompletableToListenableFutureAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -30,7 +30,9 @@
  * @author Juergen Hoeller
  * @since 4.2
  * @param <T> the result type returned by this Future's {@code get} method
+ * @deprecated as of 6.0, with no concrete replacement
  */
+@Deprecated
 public class CompletableToListenableFutureAdapter<T> implements ListenableFuture<T> {
 
 	private final CompletableFuture<T> completableFuture;