001/*
002 * Copyright (C) 2011 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.cache;
016
017import com.google.common.annotations.GwtIncompatible;
018import com.google.common.base.Preconditions;
019import com.google.common.collect.ImmutableMap;
020import java.util.concurrent.ExecutionException;
021
022/**
023 * A cache which forwards all its method calls to another cache. Subclasses should override one or
024 * more methods to modify the behavior of the backing cache as desired per the
025 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
026 *
027 * <p>Note that {@link #get}, {@link #getUnchecked}, and {@link #apply} all expose the same
028 * underlying functionality, so should probably be overridden as a group.
029 *
030 * @author Charles Fry
031 * @since 11.0
032 */
033@GwtIncompatible
034public abstract class ForwardingLoadingCache<K, V> extends ForwardingCache<K, V>
035    implements LoadingCache<K, V> {
036
037  /** Constructor for use by subclasses. */
038  protected ForwardingLoadingCache() {}
039
040  @Override
041  protected abstract LoadingCache<K, V> delegate();
042
043  @Override
044  public V get(K key) throws ExecutionException {
045    return delegate().get(key);
046  }
047
048  @Override
049  public V getUnchecked(K key) {
050    return delegate().getUnchecked(key);
051  }
052
053  @Override
054  public ImmutableMap<K, V> getAll(Iterable<? extends K> keys) throws ExecutionException {
055    return delegate().getAll(keys);
056  }
057
058  @Override
059  public V apply(K key) {
060    return delegate().apply(key);
061  }
062
063  @Override
064  public void refresh(K key) {
065    delegate().refresh(key);
066  }
067
068  /**
069   * A simplified version of {@link ForwardingLoadingCache} where subclasses can pass in an already
070   * constructed {@link LoadingCache} as the delegate.
071   *
072   * @since 10.0
073   */
074  public abstract static class SimpleForwardingLoadingCache<K, V>
075      extends ForwardingLoadingCache<K, V> {
076    private final LoadingCache<K, V> delegate;
077
078    protected SimpleForwardingLoadingCache(LoadingCache<K, V> delegate) {
079      this.delegate = Preconditions.checkNotNull(delegate);
080    }
081
082    @Override
083    protected final LoadingCache<K, V> delegate() {
084      return delegate;
085    }
086  }
087}