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Java > Open Source Codes > org > apache > commons > discovery > tools > EnvironmentCache


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61
62 package org.apache.commons.discovery.tools;
63
64 import java.util.HashMap JavaDoc;
65
66 import org.apache.commons.discovery.jdk.JDKHooks;
67
68
69 /**
70  * Cache by a 'key' unique to the environment:
71  *
72  * - ClassLoader::groupContext::Object Cache
73  * Cache : HashMap
74  * Key : Thread Context Class Loader (<code>ClassLoader</code>)
75  * Value : groupContext::SPI Cache (<code>HashMap</code>)
76  *
77  * //- groupContext::Object Cache
78  * // Cache : HashMap
79  * // Key : groupContext (<code>String</code>)
80  * // Value : <code>Object</code>
81  *
82  * When we 'release', it is expected that the caller of the 'release'
83  * have the same thread context class loader... as that will be used
84  * to identify cached entries to be released.
85  *
86  * @author Richard A. Sitze
87  */
88 public class EnvironmentCache {
89     /**
90      * Allows null key, important as default groupContext is null.
91      *
92      * We will manage synchronization directly, so all caches are implemented
93      * as HashMap (unsynchronized).
94      *
95      */
96     private static final HashMap JavaDoc root_cache = new HashMap JavaDoc();
97
98     /**
99      * Initial hash size for SPI's, default just seem TO big today..
100      */
101     public static final int smallHashSize = 13;
102     
103     /**
104      * Get object keyed by classLoader.
105      */
106     public static synchronized Object JavaDoc get(ClassLoader JavaDoc classLoader)
107     {
108         /**
109          * 'null' (bootstrap/system class loader) thread context class loader
110          * is ok... Until we learn otherwise.
111          */
112         return root_cache.get(classLoader);
113     }
114     
115     /**
116      * Put service keyed by spi & classLoader.
117      */
118     public static synchronized void put(ClassLoader JavaDoc classLoader, Object JavaDoc object)
119     {
120         /**
121          * 'null' (bootstrap/system class loader) thread context class loader
122          * is ok... Until we learn otherwise.
123          */
124         if (object != null) {
125             root_cache.put(classLoader, object);
126         }
127     }
128
129
130     /********************** CACHE-MANAGEMENT SUPPORT **********************/
131     
132     /**
133      * Release all internal references to previously created service
134      * instances associated with the current thread context class loader.
135      * The <code>release()</code> method is called for service instances that
136      * implement the <code>Service</code> interface.
137      *
138      * This is useful in environments like servlet containers,
139      * which implement application reloading by throwing away a ClassLoader.
140      * Dangling references to objects in that class loader would prevent
141      * garbage collection.
142      */
143     public static synchronized void release() {
144         /**
145          * 'null' (bootstrap/system class loader) thread context class loader
146          * is ok... Until we learn otherwise.
147          */
148         root_cache.remove(JDKHooks.getJDKHooks().getThreadContextClassLoader());
149     }
150     
151     
152     /**
153      * Release any internal references to a previously created service
154      * instance associated with the current thread context class loader.
155      * If the SPI instance implements <code>Service</code>, then call
156      * <code>release()</code>.
157      */
158     public static synchronized void release(ClassLoader JavaDoc classLoader) {
159         /**
160          * 'null' (bootstrap/system class loader) thread context class loader
161          * is ok... Until we learn otherwise.
162          */
163         root_cache.remove(classLoader);
164     }
165 }
166
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