/*
 * Copyright 2002-2018 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.scheduling.annotation;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

import org.springframework.lang.Nullable;
import org.springframework.util.concurrent.FailureCallback;
import org.springframework.util.concurrent.ListenableFuture;
import org.springframework.util.concurrent.ListenableFutureCallback;
import org.springframework.util.concurrent.SuccessCallback;

A pass-through Future handle that can be used for method signatures which are declared with a Future return type for asynchronous execution.

As of Spring 4.1, this class implements ListenableFuture, not just plain Future, along with the corresponding support in @Async processing.

As of Spring 4.2, this class also supports passing execution exceptions back to the caller.

Author:Juergen Hoeller, Rossen Stoyanchev
Type parameters:
  • <V> – the value type
See Also:
Since:3.0
/** * A pass-through {@code Future} handle that can be used for method signatures * which are declared with a {@code Future} return type for asynchronous execution. * * <p>As of Spring 4.1, this class implements {@link ListenableFuture}, not just * plain {@link java.util.concurrent.Future}, along with the corresponding support * in {@code @Async} processing. * * <p>As of Spring 4.2, this class also supports passing execution exceptions back * to the caller. * * @author Juergen Hoeller * @author Rossen Stoyanchev * @since 3.0 * @param <V> the value type * @see Async * @see #forValue(Object) * @see #forExecutionException(Throwable) */
public class AsyncResult<V> implements ListenableFuture<V> { @Nullable private final V value; @Nullable private final Throwable executionException;
Create a new AsyncResult holder.
Params:
  • value – the value to pass through
/** * Create a new AsyncResult holder. * @param value the value to pass through */
public AsyncResult(@Nullable V value) { this(value, null); }
Create a new AsyncResult holder.
Params:
  • value – the value to pass through
/** * Create a new AsyncResult holder. * @param value the value to pass through */
private AsyncResult(@Nullable V value, @Nullable Throwable ex) { this.value = value; this.executionException = ex; } @Override public boolean cancel(boolean mayInterruptIfRunning) { return false; } @Override public boolean isCancelled() { return false; } @Override public boolean isDone() { return true; } @Override @Nullable public V get() throws ExecutionException { if (this.executionException != null) { throw (this.executionException instanceof ExecutionException ? (ExecutionException) this.executionException : new ExecutionException(this.executionException)); } return this.value; } @Override @Nullable public V get(long timeout, TimeUnit unit) throws ExecutionException { return get(); } @Override public void addCallback(ListenableFutureCallback<? super V> callback) { addCallback(callback, callback); } @Override public void addCallback(SuccessCallback<? super V> successCallback, FailureCallback failureCallback) { try { if (this.executionException != null) { failureCallback.onFailure(exposedException(this.executionException)); } else { successCallback.onSuccess(this.value); } } catch (Throwable ex) { // Ignore } } @Override public CompletableFuture<V> completable() { if (this.executionException != null) { CompletableFuture<V> completable = new CompletableFuture<>(); completable.completeExceptionally(exposedException(this.executionException)); return completable; } else { return CompletableFuture.completedFuture(this.value); } }
Create a new async result which exposes the given value from Future.get().
Params:
  • value – the value to expose
See Also:
Since:4.2
/** * Create a new async result which exposes the given value from {@link Future#get()}. * @param value the value to expose * @since 4.2 * @see Future#get() */
public static <V> ListenableFuture<V> forValue(V value) { return new AsyncResult<>(value, null); }
Create a new async result which exposes the given exception as an ExecutionException from Future.get().
Params:
See Also:
Since:4.2
/** * Create a new async result which exposes the given exception as an * {@link ExecutionException} from {@link Future#get()}. * @param ex the exception to expose (either an pre-built {@link ExecutionException} * or a cause to be wrapped in an {@link ExecutionException}) * @since 4.2 * @see ExecutionException */
public static <V> ListenableFuture<V> forExecutionException(Throwable ex) { return new AsyncResult<>(null, ex); }
Determine the exposed exception: either the cause of a given ExecutionException, or the original exception as-is.
Params:
Returns:the exposed exception
/** * Determine the exposed exception: either the cause of a given * {@link ExecutionException}, or the original exception as-is. * @param original the original as given to {@link #forExecutionException} * @return the exposed exception */
private static Throwable exposedException(Throwable original) { if (original instanceof ExecutionException) { Throwable cause = original.getCause(); if (cause != null) { return cause; } } return original; } }