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1   /*
2    *  Licensed to the Apache Software Foundation (ASF) under one
3    *  or more contributor license agreements.  See the NOTICE file
4    *  distributed with this work for additional information
5    *  regarding copyright ownership.  The ASF licenses this file
6    *  to you under the Apache License, Version 2.0 (the
7    *  "License"); you may not use this file except in compliance
8    *  with the License.  You may obtain a copy of the License at
9    *
10   *    http://www.apache.org/licenses/LICENSE-2.0
11   *
12   *  Unless required by applicable law or agreed to in writing,
13   *  software distributed under the License is distributed on an
14   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15   *  KIND, either express or implied.  See the License for the
16   *  specific language governing permissions and limitations
17   *  under the License.
18   *
19   */
20  package org.apache.mina.util;
21  
22  import java.util.Collection;
23  import java.util.Map;
24  import java.util.Set;
25  import java.util.concurrent.ConcurrentHashMap;
26  import java.util.concurrent.ConcurrentMap;
27  
28  import org.apache.mina.core.buffer.IoBuffer;
29  
30  /**
31   * This map is specially useful when reads are much more frequent than writes and 
32   * if the cost of instantiating the values is high like allocating an 
33   * {@link IoBuffer} for example.
34   *  
35   * Based on the final implementation of Memoizer written by Brian Goetz and Tim
36   * Peierls. This implementation will return an
37   * {@link UnsupportedOperationException} on each method that is not intended to
38   * be called by user code for performance reasons.
39   * 
40   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
41   * @since MINA 2.0.0-M2
42   */
43  public class LazyInitializedCacheMap<K, V> implements Map<K, V> {
44      private ConcurrentMap<K, LazyInitializer<V>> cache;
45  
46      /**
47       * This class provides a noop {@link LazyInitializer} meaning it 
48       * will return the same object it received when instantiated.
49       */
50      public class NoopInitializer extends LazyInitializer<V> {
51          private V value;
52  
53          public NoopInitializer(V value) {
54              this.value = value;
55          }
56  
57          public V init() {
58              return value;
59          }
60      }
61  
62      /**
63       * Default constructor. Uses the default parameters to initialize its internal
64       * {@link ConcurrentHashMap}.
65       */
66      public LazyInitializedCacheMap() {
67          this.cache = new ConcurrentHashMap<K, LazyInitializer<V>>();
68      }
69  
70      /**
71       * This constructor allows to provide a fine tuned {@link ConcurrentHashMap}
72       * to stick with each special case the user needs.
73       */
74      public LazyInitializedCacheMap(final ConcurrentHashMap<K, LazyInitializer<V>> map) {
75          this.cache = map;
76      }
77  
78      /**
79       * {@inheritDoc}
80       */
81      public V get(Object key) {
82          LazyInitializer<V> c = cache.get(key);
83          if (c != null) {
84              return c.get();
85          }
86  
87          return null;
88      }
89  
90      /**
91       * {@inheritDoc}
92       */
93      public V remove(Object key) {
94          LazyInitializer<V> c = cache.remove(key);
95          if (c != null) {
96              return c.get();
97          }
98  
99          return null;
100     }
101 
102     /**
103      * If the specified key is not already associated
104      * with a value, associate it with the given value.
105      * This is equivalent to
106      * <pre>
107      *   if (!map.containsKey(key))
108      *       return map.put(key, value);
109      *   else
110      *       return map.get(key);</pre>
111      * except that the action is performed atomically.
112      *
113      * @param key key with which the specified value is to be associated
114      * @param value a lazy initialized value object.
115      * 
116      * @return the previous value associated with the specified key,
117      *         or <tt>null</tt> if there was no mapping for the key
118      */
119     public V putIfAbsent(K key, LazyInitializer<V> value) {
120         LazyInitializer<V> v = cache.get(key);
121         if (v == null) {
122             v = cache.putIfAbsent(key, value);
123             if (v == null) {
124                 return value.get();
125             }
126         }
127 
128         return v.get();
129     }
130 
131     /**
132      * {@inheritDoc}
133      */
134     public V put(K key, V value) {
135         LazyInitializer<V> c = cache.put(key, new NoopInitializer(value));
136         if (c != null) {
137             return c.get();
138         }
139 
140         return null;
141     }
142 
143     /**
144      * @throws {@link UnsupportedOperationException} as this method would imply
145      *         performance drops.
146      */
147     public boolean containsValue(Object value) {
148         throw new UnsupportedOperationException();
149     }
150 
151     /**
152      * @throws {@link UnsupportedOperationException} as this method would imply
153      *         performance drops.
154      */
155     public Collection<V> values() {
156         throw new UnsupportedOperationException();
157     }
158 
159     /**
160      * @throws {@link UnsupportedOperationException} as this method would imply
161      *         performance drops.
162      */
163     public Set<java.util.Map.Entry<K, V>> entrySet() {
164         throw new UnsupportedOperationException();
165     }
166 
167     /**
168      * {@inheritDoc}
169      */
170     public void putAll(Map<? extends K, ? extends V> m) {
171         for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) {
172             cache.put(e.getKey(), new NoopInitializer(e.getValue()));
173         }
174     }
175 
176     /**
177      * @return return the values from the cache
178      */
179     public Collection<LazyInitializer<V>> getValues() {
180         return cache.values();
181     }
182 
183     /**
184      * {@inheritDoc}
185      */
186     public void clear() {
187         cache.clear();
188     }
189 
190     /**
191      * {@inheritDoc}
192      */
193     public boolean containsKey(Object key) {
194         return cache.containsKey(key);
195     }
196 
197     /**
198      * {@inheritDoc}
199      */
200     public boolean isEmpty() {
201         return cache.isEmpty();
202     }
203 
204     /**
205      * {@inheritDoc}
206      */
207     public Set<K> keySet() {
208         return cache.keySet();
209     }
210 
211     /**
212      * {@inheritDoc}
213      */
214     public int size() {
215         return cache.size();
216     }
217 }