SoftReferenceCache


1   package com.protomatter.util;
2   
3   /**
4    *  {{{ The Protomatter Software License, Version 1.0
5    *  derived from The Apache Software License, Version 1.1
6    *
7    *  Copyright (c) 1998-2002 Nate Sammons.  All rights reserved.
8    *
9    *  Redistribution and use in source and binary forms, with or without
10   *  modification, are permitted provided that the following conditions
11   *  are met:
12   *
13   *  1. Redistributions of source code must retain the above copyright
14   *     notice, this list of conditions and the following disclaimer.
15   *
16   *  2. Redistributions in binary form must reproduce the above copyright
17   *     notice, this list of conditions and the following disclaimer in
18   *     the documentation and/or other materials provided with the
19   *     distribution.
20   *
21   *  3. The end-user documentation included with the redistribution,
22   *     if any, must include the following acknowledgment:
23   *        "This product includes software developed for the
24   *         Protomatter Software Project
25   *         (http://protomatter.sourceforge.net/)."
26   *     Alternately, this acknowledgment may appear in the software itself,
27   *     if and wherever such third-party acknowledgments normally appear.
28   *
29   *  4. The names "Protomatter" and "Protomatter Software Project" must
30   *     not be used to endorse or promote products derived from this
31   *     software without prior written permission. For written
32   *     permission, please contact support@protomatter.com.
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34   *  5. Products derived from this software may not be called "Protomatter",
35   *     nor may "Protomatter" appear in their name, without prior written
36   *     permission of the Protomatter Software Project
37   *     (support@protomatter.com).
38   *
39   *  THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
40   *  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
41   *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
42   *  DISCLAIMED.  IN NO EVENT SHALL THE PROTOMATTER SOFTWARE PROJECT OR
43   *  ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
44   *  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
45   *  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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47   *  ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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49   *  OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
50   *  SUCH DAMAGE.   }}}
51   */
52  
53  import java.util.*;
54  import java.lang.ref.*;
55  
56  /**
57   *  A cache that uses soft references.  Values in this cache
58   *  are expired by the VM in reponse to memory needs.  For
59   *  more information on how this works, see the JavaDoc
60   *  for the <TT>java.lang.ref</TT> package.
61   */
62  public class SoftReferenceCache
63  implements Cache
64  {
65    private Map map = null;
66  
67    /**
68     *  Create a new cache.
69     */
70    public SoftReferenceCache()
71    {
72      clear();
73    }
74  
75    /**
76     *  Put a value into the cache, possibly clobbering
77     *  the old value if one exists.
78     */
79    public void put(Object   key, Object   val)
80    {
81      map.put(key, new SoftReference(val));
82    }
83  
84    /**
85     *  Get a value from the cache at the given key.
86     *
87     *  @return The cached value, or <TT>null</TT> if no value exists.
88     */
89    public Object   get(Object   key)
90    {
91      SoftReference ref = (SoftReference)map.get(key);
92      if (ref != null)
93      {
94        Object   o = ref.get();
95        if (o == null)
96          clear(key);
97        return o;
98      }
99      return null;
100   }
101 
102   /**
103    *  Clear the value in the cache at the given key.
104    */
105   public void clear(Object   key)
106   {
107     this.map.remove(key);
108   }
109 
110   /**
111    *  Clear the entire cache.
112    */
113   public void clear()
114   {
115     this.map = new HashMap();
116   }
117 }
118
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