1   /*
2    * Copyright (C) 2011 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.ExecutionException;
22  import java.util.concurrent.Future;
23  
24  /**
25   * Provides a backup {@code Future} to replace an earlier failed {@code Future}.
26   * An implementation of this interface can be applied to an input {@code Future}
27   * with {@link Futures#withFallback}.
28   *
29   * @param <V> the result type of the provided backup {@code Future}
30   *
31   * @author Bruno Diniz
32   * @since 14.0
33   */
34  @Beta
35  public interface FutureFallback<V> {
36    /**
37     * Returns a {@code Future} to be used in place of the {@code Future} that
38     * failed with the given exception. The exception is provided so that the
39     * {@code Fallback} implementation can conditionally determine whether to
40     * propagate the exception or to attempt to recover.
41     *
42     * @param t the exception that made the future fail. If the future's {@link
43     *     Future#get() get} method throws an {@link ExecutionException}, then the
44     *     cause is passed to this method. Any other thrown object is passed
45     *     unaltered.
46     */
47    ListenableFuture<V> create(Throwable t) throws Exception;
48  }