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Java > Open Source Codes > freemarker > cache > SoftCacheStorage


1 /*
2  * Copyright (c) 2003 The Visigoth Software Society. All rights
3  * reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  *
9  * 1. Redistributions of source code must retain the above copyright
10  * notice, this list of conditions and the following disclaimer.
11  *
12  * 2. Redistributions in binary form must reproduce the above copyright
13  * notice, this list of conditions and the following disclaimer in
14  * the documentation and/or other materials provided with the
15  * distribution.
16  *
17  * 3. The end-user documentation included with the redistribution, if
18  * any, must include the following acknowledgement:
19  * "This product includes software developed by the
20  * Visigoth Software Society (http://www.visigoths.org/)."
21  * Alternately, this acknowledgement may appear in the software itself,
22  * if and wherever such third-party acknowledgements normally appear.
23  *
24  * 4. Neither the name "FreeMarker", "Visigoth", nor any of the names of the
25  * project contributors may be used to endorse or promote products derived
26  * from this software without prior written permission. For written
27  * permission, please contact visigoths@visigoths.org.
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29  * 5. Products derived from this software may not be called "FreeMarker" or "Visigoth"
30  * nor may "FreeMarker" or "Visigoth" appear in their names
31  * without prior written permission of the Visigoth Software Society.
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33  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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48  * individuals on behalf of the Visigoth Software Society. For more
49  * information on the Visigoth Software Society, please see
50  * http://www.visigoths.org/
51  */

52
53 package freemarker.cache;
54
55 import java.lang.ref.Reference JavaDoc;
56 import java.lang.ref.ReferenceQueue JavaDoc;
57 import java.lang.ref.SoftReference JavaDoc;
58 import java.util.HashMap JavaDoc;
59 import java.util.Map JavaDoc;
60
61 /**
62  * Strong cache storage is a cache storage that uses {@link SoftReference}
63  * objects to hold the objects it was passed, therefore allows the garbage
64  * collector to purge the cache when it determines that it wants to free up
65  * memory.
66  * This class is <em>NOT</em> thread-safe. If it is accessed from multiple
67  * threads concurrently, proper synchronization must be provided by the callers.
68  * Note that {@link TemplateCache}, the natural user of this class provides the
69  * necessary synchronizations when it uses the class.
70  * @author Attila Szegedi
71  * @version $Id: SoftCacheStorage.java,v 1.4 2003/09/22 20:47:03 ddekany Exp $
72  *
73  * @deprecated use {@link MruCacheStorage} instead.
74  */

75 public class SoftCacheStorage implements CacheStorage
76 {
77     private final ReferenceQueue JavaDoc queue = new ReferenceQueue JavaDoc();
78     private final Map JavaDoc map;
79     
80     public SoftCacheStorage()
81     {
82         this(new HashMap JavaDoc());
83     }
84     
85     public SoftCacheStorage(Map JavaDoc backingMap)
86     {
87         this.map = backingMap;
88     }
89     
90     public Object JavaDoc get(Object JavaDoc key)
91     {
92         processQueue();
93         Reference JavaDoc ref = (Reference JavaDoc)map.get(key);
94         return ref == null ? null : ref.get();
95     }
96
97     public void put(Object JavaDoc key, Object JavaDoc value)
98     {
99         processQueue();
100         map.put(key, new SoftValueReference(key, value, queue));
101     }
102
103     public void remove(Object JavaDoc key)
104     {
105         processQueue();
106         map.remove(key);
107     }
108
109     public void clear()
110     {
111         map.clear();
112         processQueue();
113     }
114
115     private void processQueue()
116     {
117         for(;;)
118         {
119             SoftValueReference ref = (SoftValueReference)queue.poll();
120             if(ref == null)
121             {
122                 return;
123             }
124             Object JavaDoc key = ref.getKey();
125             // First check for reference identity, so that we don't remove
126
// a reloaded template with the same key inadvertently.
127
if(map.get(key) == ref)
128             {
129                 map.remove(key);
130             }
131         }
132     }
133
134     private static final class SoftValueReference
135     extends
136         SoftReference JavaDoc
137     {
138         private final Object JavaDoc key;
139
140         SoftValueReference(Object JavaDoc key, Object JavaDoc value, ReferenceQueue JavaDoc queue)
141         {
142             super(value, queue);
143             this.key = key;
144         }
145
146         Object JavaDoc getKey()
147         {
148             return key;
149         }
150     }
151 }
152
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