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    
017    package com.google.common.util.concurrent;
018    
019    import com.google.common.annotations.Beta;
020    
021    import java.util.concurrent.CancellationException;
022    import java.util.concurrent.ExecutionException;
023    import java.util.concurrent.Future;
024    import java.util.concurrent.TimeUnit;
025    import java.util.concurrent.TimeoutException;
026    
027    /**
028     * A {@code CheckedFuture} is a {@link ListenableFuture} that includes versions
029     * of the {@code get} methods that can throw a checked exception.  This makes it
030     * easier to create a future that executes logic which can throw an exception.
031     *
032     * <p>A common implementation is {@link Futures#immediateCheckedFuture}.
033     *
034     * <p>Implementations of this interface must adapt the exceptions thrown by
035     * {@code Future#get()}: {@link CancellationException},
036     * {@link ExecutionException} and {@link InterruptedException} into the type
037     * specified by the {@code E} type parameter.
038     *
039     * <p>This interface also extends the ListenableFuture interface to allow
040     * listeners to be added. This allows the future to be used as a normal
041     * {@link Future} or as an asynchronous callback mechanism as needed. This
042     * allows multiple callbacks to be registered for a particular task, and the
043     * future will guarantee execution of all listeners when the task completes.
044     * 
045     * <p>For a simpler alternative to CheckedFuture, consider accessing Future 
046     * values with {@link Futures#get(Future, Class) Futures.get()}.
047     *
048     * @author Sven Mawson
049     * @since 1.0
050     */
051    @Beta
052    public interface CheckedFuture<V, X extends Exception>
053        extends ListenableFuture<V> {
054    
055      /**
056       * Exception checking version of {@link Future#get()} that will translate
057       * {@link InterruptedException}, {@link CancellationException} and
058       * {@link ExecutionException} into application-specific exceptions.
059       *
060       * @return the result of executing the future.
061       * @throws X on interruption, cancellation or execution exceptions.
062       */
063      V checkedGet() throws X;
064    
065      /**
066       * Exception checking version of {@link Future#get(long, TimeUnit)} that will
067       * translate {@link InterruptedException}, {@link CancellationException} and
068       * {@link ExecutionException} into application-specific exceptions.  On
069       * timeout this method throws a normal {@link TimeoutException}.
070       *
071       * @return the result of executing the future.
072       * @throws TimeoutException if retrieving the result timed out.
073       * @throws X on interruption, cancellation or execution exceptions.
074       */
075      V checkedGet(long timeout, TimeUnit unit) throws TimeoutException, X;
076    }