001/*
002 * Copyright (C) 2008 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.util.concurrent;
018
019import com.google.common.annotations.Beta;
020import com.google.common.annotations.GwtCompatible;
021
022import java.util.concurrent.CancellationException;
023import java.util.concurrent.ExecutionException;
024import java.util.concurrent.Future;
025import java.util.concurrent.TimeUnit;
026import java.util.concurrent.TimeoutException;
027
028/**
029 * A {@code CheckedFuture} is a {@link ListenableFuture} that includes versions
030 * of the {@code get} methods that can throw a checked exception.  This makes it
031 * easier to create a future that executes logic which can throw an exception.
032 *
033 * <p>A common implementation is {@link Futures#immediateCheckedFuture}.
034 *
035 * <p>Implementations of this interface must adapt the exceptions thrown by
036 * {@code Future#get()}: {@link CancellationException},
037 * {@link ExecutionException} and {@link InterruptedException} into the type
038 * specified by the {@code X} type parameter.
039 *
040 * <p>This interface also extends the ListenableFuture interface to allow
041 * listeners to be added. This allows the future to be used as a normal
042 * {@link Future} or as an asynchronous callback mechanism as needed. This
043 * allows multiple callbacks to be registered for a particular task, and the
044 * future will guarantee execution of all listeners when the task completes.
045 * 
046 * <p>For a simpler alternative to CheckedFuture, consider accessing Future 
047 * values with {@link Futures#getChecked(Future, Class) Futures.getChecked()}.
048 *
049 * @author Sven Mawson
050 * @since 1.0
051 */
052@Beta
053@GwtCompatible
054public interface CheckedFuture<V, X extends Exception>
055    extends ListenableFuture<V> {
056
057  /**
058   * Exception checking version of {@link Future#get()} that will translate
059   * {@link InterruptedException}, {@link CancellationException} and
060   * {@link ExecutionException} into application-specific exceptions.
061   *
062   * @return the result of executing the future.
063   * @throws X on interruption, cancellation or execution exceptions.
064   */
065  V checkedGet() throws X;
066
067  /**
068   * Exception checking version of {@link Future#get(long, TimeUnit)} that will
069   * translate {@link InterruptedException}, {@link CancellationException} and
070   * {@link ExecutionException} into application-specific exceptions.  On
071   * timeout this method throws a normal {@link TimeoutException}.
072   *
073   * @return the result of executing the future.
074   * @throws TimeoutException if retrieving the result timed out.
075   * @throws X on interruption, cancellation or execution exceptions.
076   */
077  V checkedGet(long timeout, TimeUnit unit) throws TimeoutException, X;
078}