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.cache;
018
019import com.google.common.base.Preconditions;
020import com.google.common.collect.ImmutableMap;
021
022import java.util.concurrent.ExecutionException;
023
024/**
025 * A cache which forwards all its method calls to another cache. Subclasses should override one or
026 * more methods to modify the behavior of the backing cache as desired per the
027 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
028 *
029 * <p>Note that {@link #get}, {@link #getUnchecked}, and {@link #apply} all expose the same
030 * underlying functionality, so should probably be overridden as a group.
031 *
032 * @author Charles Fry
033 * @since 11.0
034 */
035public abstract class ForwardingLoadingCache<K, V>
036    extends ForwardingCache<K, V> implements LoadingCache<K, V> {
037
038  /** Constructor for use by subclasses. */
039  protected ForwardingLoadingCache() {}
040
041  @Override
042  protected abstract LoadingCache<K, V> delegate();
043
044  @Override
045  public V get(K key) throws ExecutionException {
046    return delegate().get(key);
047  }
048
049  @Override
050  public V getUnchecked(K key) {
051    return delegate().getUnchecked(key);
052  }
053
054  @Override
055  public ImmutableMap<K, V> getAll(Iterable<? extends K> keys) throws ExecutionException {
056    return delegate().getAll(keys);
057  }
058
059  @Override
060  public V apply(K key) {
061    return delegate().apply(key);
062  }
063
064  @Override
065  public void refresh(K key) {
066    delegate().refresh(key);
067  }
068
069  /**
070   * A simplified version of {@link ForwardingLoadingCache} where subclasses can pass in an already
071   * constructed {@link LoadingCache} as the delegate.
072   *
073   * @since 10.0
074   */
075  public abstract static class SimpleForwardingLoadingCache<K, V>
076      extends ForwardingLoadingCache<K, V> {
077    private final LoadingCache<K, V> delegate;
078
079    protected SimpleForwardingLoadingCache(LoadingCache<K, V> delegate) {
080      this.delegate = Preconditions.checkNotNull(delegate);
081    }
082
083    @Override
084    protected final LoadingCache<K, V> delegate() {
085      return delegate;
086    }
087  }
088}