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    
017    package com.google.common.cache;
018    
019    import com.google.common.annotations.Beta;
020    import com.google.common.base.Preconditions;
021    import com.google.common.collect.ForwardingObject;
022    
023    import javax.annotation.Nullable;
024    
025    import java.util.concurrent.ConcurrentMap;
026    import java.util.concurrent.ExecutionException;
027    
028    /**
029     * A cache which forwards all its method calls to another cache. Subclasses should override one or
030     * more methods to modify the behavior of the backing cache as desired per the
031     * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
032     *
033     * <p>Note that {@link #get}, {@link #getUnchecked}, and {@link #apply} all expose the same
034     * underlying functionality, so should probably be overridden as a group.
035     *
036     * @author Charles Fry
037     * @since 10.0
038     */
039    @Beta
040    public abstract class ForwardingCache<K, V> extends ForwardingObject implements Cache<K, V> {
041    
042      /** Constructor for use by subclasses. */
043      protected ForwardingCache() {}
044    
045      @Override
046      protected abstract Cache<K, V> delegate();
047    
048      @Override
049      @Nullable
050      public V get(@Nullable K key) throws ExecutionException {
051        return delegate().get(key);
052      }
053    
054      @Override
055      @Nullable
056      public V getUnchecked(@Nullable K key) {
057        return delegate().getUnchecked(key);
058      }
059    
060      @Deprecated
061      @Override
062      @Nullable
063      public V apply(@Nullable K key) {
064        return delegate().apply(key);
065      }
066    
067      @Override
068      public void invalidate(@Nullable Object key) {
069        delegate().invalidate(key);
070      }
071    
072      @Override
073      public void invalidateAll() {
074        delegate().invalidateAll();
075      }
076    
077      @Override
078      public long size() {
079        return delegate().size();
080      }
081    
082      @Override
083      public CacheStats stats() {
084        return delegate().stats();
085      }
086    
087      @Override
088      public ConcurrentMap<K, V> asMap() {
089        return delegate().asMap();
090      }
091    
092      @Override
093      public void cleanUp() {
094        delegate().cleanUp();
095      }
096    
097      /**
098       * A simplified version of {@link ForwardingCache} where subclasses can pass in an already
099       * constructed {@link Cache} as the delegete.
100       *
101       * @since 10.0
102       */
103      @Beta
104      public abstract static class SimpleForwardingCache<K, V> extends ForwardingCache<K, V> {
105        private final Cache<K, V> delegate;
106    
107        protected SimpleForwardingCache(Cache<K, V> delegate) {
108          this.delegate = Preconditions.checkNotNull(delegate);
109        }
110    
111        @Override
112        protected final Cache<K, V> delegate() {
113          return delegate;
114        }
115      }
116    }