001    /*
002     * Copyright (C) 2008 Google Inc.
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 an extension of {@link Future} that includes
029     * versions of the {@code get} methods that can throw a checked exception and
030     * allows listeners to be attached to the future.  This makes it easier to
031     * create a future that executes logic which can throw an exception.
032     * 
033     * <p>Implementations of this interface must adapt the exceptions thrown by
034     * {@code Future#get()}: {@link CancellationException},
035     * {@link ExecutionException} and {@link InterruptedException} into the type
036     * specified by the {@code E} type parameter.
037     * 
038     * <p>This interface also extends the ListenableFuture interface to allow
039     * listeners to be added. This allows the future to be used as a normal
040     * {@link Future} or as an asynchronous callback mechanism as needed. This
041     * allows multiple callbacks to be registered for a particular task, and the
042     * future will guarantee execution of all listeners when the task completes.
043     * 
044     * @author Sven Mawson
045     * @since 1
046     */
047    @Beta
048    public interface CheckedFuture<V, E extends Exception>
049        extends ListenableFuture<V> {
050    
051      /**
052       * Exception checking version of {@link Future#get()} that will translate
053       * {@link InterruptedException}, {@link CancellationException} and
054       * {@link ExecutionException} into application-specific exceptions.
055       * 
056       * @return the result of executing the future.
057       * @throws E on interruption, cancellation or execution exceptions.
058       */
059      V checkedGet() throws E;
060      
061      /**
062       * Exception checking version of {@link Future#get(long, TimeUnit)} that will
063       * translate {@link InterruptedException}, {@link CancellationException} and
064       * {@link ExecutionException} into application-specific exceptions.  On
065       * timeout this method throws a normal {@link TimeoutException}.
066       * 
067       * @return the result of executing the future.
068       * @throws TimeoutException if retrieving the result timed out.
069       * @throws E on interruption, cancellation or execution exceptions.
070       */
071      V checkedGet(long timeout, TimeUnit unit) throws TimeoutException, E;
072    }