1   /*
2    * Copyright (C) 2008 The Guava Authors
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    * http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  
17  package com.google.common.util.concurrent;
18  
19  import com.google.common.annotations.Beta;
20  
21  import java.util.concurrent.CancellationException;
22  import java.util.concurrent.ExecutionException;
23  import java.util.concurrent.Future;
24  import java.util.concurrent.TimeUnit;
25  import java.util.concurrent.TimeoutException;
26  
27  /**
28   * A {@code CheckedFuture} is a {@link ListenableFuture} that includes versions
29   * of the {@code get} methods that can throw a checked exception.  This makes it
30   * easier to create a future that executes logic which can throw an exception.
31   *
32   * <p>A common implementation is {@link Futures#immediateCheckedFuture}.
33   *
34   * <p>Implementations of this interface must adapt the exceptions thrown by
35   * {@code Future#get()}: {@link CancellationException},
36   * {@link ExecutionException} and {@link InterruptedException} into the type
37   * specified by the {@code X} type parameter.
38   *
39   * <p>This interface also extends the ListenableFuture interface to allow
40   * listeners to be added. This allows the future to be used as a normal
41   * {@link Future} or as an asynchronous callback mechanism as needed. This
42   * allows multiple callbacks to be registered for a particular task, and the
43   * future will guarantee execution of all listeners when the task completes.
44   * 
45   * <p>For a simpler alternative to CheckedFuture, consider accessing Future 
46   * values with {@link Futures#get(Future, Class) Futures.get()}.
47   *
48   * @author Sven Mawson
49   * @since 1.0
50   */
51  @Beta
52  public interface CheckedFuture<V, X extends Exception>
53      extends ListenableFuture<V> {
54  
55    /**
56     * Exception checking version of {@link Future#get()} that will translate
57     * {@link InterruptedException}, {@link CancellationException} and
58     * {@link ExecutionException} into application-specific exceptions.
59     *
60     * @return the result of executing the future.
61     * @throws X on interruption, cancellation or execution exceptions.
62     */
63    V checkedGet() throws X;
64  
65    /**
66     * Exception checking version of {@link Future#get(long, TimeUnit)} that will
67     * translate {@link InterruptedException}, {@link CancellationException} and
68     * {@link ExecutionException} into application-specific exceptions.  On
69     * timeout this method throws a normal {@link TimeoutException}.
70     *
71     * @return the result of executing the future.
72     * @throws TimeoutException if retrieving the result timed out.
73     * @throws X on interruption, cancellation or execution exceptions.
74     */
75    V checkedGet(long timeout, TimeUnit unit) throws TimeoutException, X;
76  }