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  
17  package com.google.common.cache;
18  
19  import com.google.common.annotations.Beta;
20  import com.google.common.base.Preconditions;
21  import com.google.common.collect.ImmutableMap;
22  
23  import 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
37  public 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  }