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
17package com.google.common.cache;
18
19import com.google.common.annotations.Beta;
20import com.google.common.base.Preconditions;
21import com.google.common.collect.ImmutableMap;
22
23import java.util.concurrent.ExecutionException;
24
25/**
26 * A cache which forwards all its method calls to another cache. Subclasses should override one or
27 * more methods to modify the behavior of the backing cache as desired per the
28 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
29 *
30 * <p>Note that {@link #get}, {@link #getUnchecked}, and {@link #apply} all expose the same
31 * underlying functionality, so should probably be overridden as a group.
32 *
33 * @author Charles Fry
34 * @since 11.0
35 */
36@Beta
37public abstract class ForwardingLoadingCache<K, V>
38    extends ForwardingCache<K, V> implements LoadingCache<K, V> {
39
40  /** Constructor for use by subclasses. */
41  protected ForwardingLoadingCache() {}
42
43  @Override
44  protected abstract LoadingCache<K, V> delegate();
45
46  @Override
47  public V get(K key) throws ExecutionException {
48    return delegate().get(key);
49  }
50
51  @Override
52  public V getUnchecked(K key) {
53    return delegate().getUnchecked(key);
54  }
55
56  @Override
57  public ImmutableMap<K, V> getAll(Iterable<? extends K> keys) throws ExecutionException {
58    return delegate().getAll(keys);
59  }
60
61  @Override
62  public V apply(K key) {
63    return delegate().apply(key);
64  }
65
66  @Override
67  public void refresh(K key) {
68    delegate().refresh(key);
69  }
70
71  /**
72   * A simplified version of {@link ForwardingLoadingCache} where subclasses can pass in an already
73   * constructed {@link LoadingCache} as the delegete.
74   *
75   * @since 10.0
76   */
77  @Beta
78  public abstract static class SimpleForwardingLoadingCache<K, V>
79      extends ForwardingLoadingCache<K, V> {
80    private final LoadingCache<K, V> delegate;
81
82    protected SimpleForwardingLoadingCache(LoadingCache<K, V> delegate) {
83      this.delegate = Preconditions.checkNotNull(delegate);
84    }
85
86    @Override
87    protected final LoadingCache<K, V> delegate() {
88      return delegate;
89    }
90  }
91}
92