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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      * {@inheritDoc}
    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 }