1 /*
2  * Copyright (C) 2011 The Guava Authors
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
5  * in compliance with the License. You may obtain a copy of the License at
6  *
7  * http://www.apache.org/licenses/LICENSE-2.0
8  *
9  * Unless required by applicable law or agreed to in writing, software distributed under the License
10  * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
11  * or implied. See the License for the specific language governing permissions and limitations under
12  * the License.
13  */
14 
15 package com.google.common.cache;
16 
17 import com.google.common.annotations.GwtIncompatible;
18 import com.google.common.base.Preconditions;
19 import com.google.common.collect.ImmutableMap;
20 import java.util.concurrent.ExecutionException;
21 
22 /**
23  * A cache which forwards all its method calls to another cache. Subclasses should override one or
24  * more methods to modify the behavior of the backing cache as desired per the <a
25  * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
26  *
27  * <p>Note that {@link #get}, {@link #getUnchecked}, and {@link #apply} all expose the same
28  * underlying functionality, so should probably be overridden as a group.
29  *
30  * @author Charles Fry
31  * @since 11.0
32  */
33 @GwtIncompatible
34 public abstract class ForwardingLoadingCache<K, V> extends ForwardingCache<K, V>
35     implements LoadingCache<K, V> {
36 
37   /** Constructor for use by subclasses. */
ForwardingLoadingCache()38   protected ForwardingLoadingCache() {}
39 
40   @Override
delegate()41   protected abstract LoadingCache<K, V> delegate();
42 
43   @Override
get(K key)44   public V get(K key) throws ExecutionException {
45     return delegate().get(key);
46   }
47 
48   @Override
getUnchecked(K key)49   public V getUnchecked(K key) {
50     return delegate().getUnchecked(key);
51   }
52 
53   @Override
getAll(Iterable<? extends K> keys)54   public ImmutableMap<K, V> getAll(Iterable<? extends K> keys) throws ExecutionException {
55     return delegate().getAll(keys);
56   }
57 
58   @Override
apply(K key)59   public V apply(K key) {
60     return delegate().apply(key);
61   }
62 
63   @Override
refresh(K key)64   public void refresh(K key) {
65     delegate().refresh(key);
66   }
67 
68   /**
69    * A simplified version of {@link ForwardingLoadingCache} where subclasses can pass in an already
70    * constructed {@link LoadingCache} as the delegate.
71    *
72    * @since 10.0
73    */
74   public abstract static class SimpleForwardingLoadingCache<K, V>
75       extends ForwardingLoadingCache<K, V> {
76     private final LoadingCache<K, V> delegate;
77 
SimpleForwardingLoadingCache(LoadingCache<K, V> delegate)78     protected SimpleForwardingLoadingCache(LoadingCache<K, V> delegate) {
79       this.delegate = Preconditions.checkNotNull(delegate);
80     }
81 
82     @Override
delegate()83     protected final LoadingCache<K, V> delegate() {
84       return delegate;
85     }
86   }
87 }
88