001/*
002 * Copyright (C) 2011 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
017package com.google.common.util.concurrent;
018
019import com.google.common.annotations.Beta;
020
021import java.util.concurrent.ExecutionException;
022import java.util.concurrent.Future;
023
024/**
025 * Provides a backup {@code Future} to replace an earlier failed {@code Future}.
026 * An implementation of this interface can be applied to an input {@code Future}
027 * with {@link Futures#withFallback}.
028 *
029 * @param <V> the result type of the provided backup {@code Future}
030 *
031 * @author Bruno Diniz
032 * @since 14.0
033 */
034@Beta
035public interface FutureFallback<V> {
036  /**
037   * Returns a {@code Future} to be used in place of the {@code Future} that
038   * failed with the given exception. The exception is provided so that the
039   * {@code Fallback} implementation can conditionally determine whether to
040   * propagate the exception or to attempt to recover.
041   *
042   * @param t the exception that made the future fail. If the future's {@link
043   *     Future#get() get} method throws an {@link ExecutionException}, then the
044   *     cause is passed to this method. Any other thrown object is passed
045   *     unaltered.
046   */
047  ListenableFuture<V> create(Throwable t) throws Exception;
048}