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.TimeUnit;
24  import java.util.concurrent.TimeoutException;
25  
26  /**
27   * A delegating wrapper around a {@link ListenableFuture} that adds support for
28   * the {@link #checkedGet()} and {@link #checkedGet(long, TimeUnit)} methods.
29   *
30   * @author Sven Mawson
31   * @since 1.0
32   */
33  @Beta
34  public abstract class AbstractCheckedFuture<V, X extends Exception>
35      extends ForwardingListenableFuture.SimpleForwardingListenableFuture<V>
36      implements CheckedFuture<V, X> {
37    /**
38     * Constructs an {@code AbstractCheckedFuture} that wraps a delegate.
39     */
40    protected AbstractCheckedFuture(ListenableFuture<V> delegate) {
41      super(delegate);
42    }
43  
44    /**
45     * Translates from an {@link InterruptedException},
46     * {@link CancellationException} or {@link ExecutionException} thrown by
47     * {@code get} to an exception of type {@code X} to be thrown by
48     * {@code checkedGet}. Subclasses must implement this method.
49     *
50     * <p>If {@code e} is an {@code InterruptedException}, the calling
51     * {@code checkedGet} method has already restored the interrupt after catching
52     * the exception. If an implementation of {@link #mapException(Exception)}
53     * wishes to swallow the interrupt, it can do so by calling
54     * {@link Thread#interrupted()}.
55     *
56     * <p>Subclasses may choose to throw, rather than return, a subclass of
57     * {@code RuntimeException} to allow creating a CheckedFuture that throws
58     * both checked and unchecked exceptions.
59     */
60    protected abstract X mapException(Exception e);
61  
62    /**
63     * {@inheritDoc}
64     *
65     * <p>This implementation calls {@link #get()} and maps that method's standard
66     * exceptions to instances of type {@code X} using {@link #mapException}.
67     *
68     * <p>In addition, if {@code get} throws an {@link InterruptedException}, this
69     * implementation will set the current thread's interrupt status before
70     * calling {@code mapException}.
71     *
72     * @throws X if {@link #get()} throws an {@link InterruptedException},
73     *         {@link CancellationException}, or {@link ExecutionException}
74     */
75    @Override
76    public V checkedGet() throws X {
77      try {
78        return get();
79      } catch (InterruptedException e) {
80        Thread.currentThread().interrupt();
81        throw mapException(e);
82      } catch (CancellationException e) {
83        throw mapException(e);
84      } catch (ExecutionException e) {
85        throw mapException(e);
86      }
87    }
88  
89    /**
90     * {@inheritDoc}
91     *
92     * <p>This implementation calls {@link #get(long, TimeUnit)} and maps that
93     * method's standard exceptions (excluding {@link TimeoutException}, which is
94     * propagated) to instances of type {@code X} using {@link #mapException}.
95     *
96     * <p>In addition, if {@code get} throws an {@link InterruptedException}, this
97     * implementation will set the current thread's interrupt status before
98     * calling {@code mapException}.
99     *
100    * @throws X if {@link #get()} throws an {@link InterruptedException},
101    *         {@link CancellationException}, or {@link ExecutionException}
102    * @throws TimeoutException {@inheritDoc}
103    */
104   @Override
105   public V checkedGet(long timeout, TimeUnit unit) throws TimeoutException, X {
106     try {
107       return get(timeout, unit);
108     } catch (InterruptedException e) {
109       Thread.currentThread().interrupt();
110       throw mapException(e);
111     } catch (CancellationException e) {
112       throw mapException(e);
113     } catch (ExecutionException e) {
114       throw mapException(e);
115     }
116   }
117 }