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.annotations.Beta;
020import com.google.common.base.Preconditions;
021import com.google.common.collect.ImmutableMap;
022
023import java.util.concurrent.ExecutionException;
024
025/**
026 * A cache which forwards all its method calls to another cache. Subclasses should override one or
027 * more methods to modify the behavior of the backing cache as desired per the
028 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
029 *
030 * <p>Note that {@link #get}, {@link #getUnchecked}, and {@link #apply} all expose the same
031 * underlying functionality, so should probably be overridden as a group.
032 *
033 * @author Charles Fry
034 * @since 11.0
035 */
036@Beta
037public abstract class ForwardingLoadingCache<K, V>
038    extends ForwardingCache<K, V> implements LoadingCache<K, V> {
039
040  /** Constructor for use by subclasses. */
041  protected ForwardingLoadingCache() {}
042
043  @Override
044  protected abstract LoadingCache<K, V> delegate();
045
046  @Override
047  public V get(K key) throws ExecutionException {
048    return delegate().get(key);
049  }
050
051  @Override
052  public V getUnchecked(K key) {
053    return delegate().getUnchecked(key);
054  }
055
056  @Override
057  public ImmutableMap<K, V> getAll(Iterable<? extends K> keys) throws ExecutionException {
058    return delegate().getAll(keys);
059  }
060
061  @Override
062  public V apply(K key) {
063    return delegate().apply(key);
064  }
065
066  @Override
067  public void refresh(K key) {
068    delegate().refresh(key);
069  }
070
071  /**
072   * A simplified version of {@link ForwardingLoadingCache} where subclasses can pass in an already
073   * constructed {@link LoadingCache} as the delegete.
074   *
075   * @since 10.0
076   */
077  @Beta
078  public abstract static class SimpleForwardingLoadingCache<K, V>
079      extends ForwardingLoadingCache<K, V> {
080    private final LoadingCache<K, V> delegate;
081
082    protected SimpleForwardingLoadingCache(LoadingCache<K, V> delegate) {
083      this.delegate = Preconditions.checkNotNull(delegate);
084    }
085
086    @Override
087    protected final LoadingCache<K, V> delegate() {
088      return delegate;
089    }
090  }
091}