KickJava   Java API By Example, From Geeks To Geeks.

Java > Open Source Codes > org > apache > ojb > broker > cache > ObjectCacheLocalDefaultImpl


1 package org.apache.ojb.broker.cache;
2
3 /* Copyright 2003-2005 The Apache Software Foundation
4  *
5  * Licensed under the Apache License, Version 2.0 (the "License");
6  * you may not use this file except in compliance with the License.
7  * You may obtain a copy of the License at
8  *
9  * http://www.apache.org/licenses/LICENSE-2.0
10  *
11  * Unless required by applicable law or agreed to in writing, software
12  * distributed under the License is distributed on an "AS IS" BASIS,
13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14  * See the License for the specific language governing permissions and
15  * limitations under the License.
16  */
17
18 import org.apache.commons.lang.builder.ToStringBuilder;
19 import org.apache.commons.lang.builder.ToStringStyle;
20 import org.apache.ojb.broker.Identity;
21 import org.apache.ojb.broker.PersistenceBroker;
22
23 import java.lang.ref.SoftReference JavaDoc;
24 import java.util.HashMap JavaDoc;
25 import java.util.Map JavaDoc;
26 import java.util.Properties JavaDoc;
27
28 /**
29  * Simple, flexible local {@link ObjectCache} implementation using a
30  * {@link java.util.HashMap} to cache given objects.
31  * <p>
32  * The cache uses soft-references which allows objects (softly) referenced by
33  * the cache to be reclaimed by the Java Garbage Collector when they are not
34  * longer referenced elsewhere.
35  * </p>
36  * <p>
37  * NOTE: Handle with care! If multiple PB instances are used (OJB standard behavior) you
38  * will run into synchronization problems.
39  * </p>
40  * <p>
41  * Implementation configuration properties:
42  * </p>
43  *
44  * <table cellspacing="2" cellpadding="2" border="3" frame="box">
45  * <tr>
46  * <td><strong>Property Key</strong></td>
47  * <td><strong>Property Values</strong></td>
48  * </tr>
49  * <tr>
50  * <td>timeout</td>
51  * <td>
52  * Lifetime of the cached objects in seconds.
53  * If expired the cached object was not returned
54  * on lookup call (and removed from cache).
55  * </td>
56  * </tr>
57  * </table>
58  *
59  * <br/>
60  *
61  * @author <a HREF="mailto:thma@apache.org">Thomas Mahler<a>
62  * @author <a HREF="mailto:armin@codeAuLait.de">Armin Waibel</a>
63  * @version $Id: ObjectCacheLocalDefaultImpl.java,v 1.5.2.2 2005/12/21 22:24:15 tomdz Exp $
64  */
65 public class ObjectCacheLocalDefaultImpl implements ObjectCache
66 {
67     private static final String JavaDoc TIMEOUT = "timeout";
68
69     /**
70      * the hashtable holding all cached object
71      */
72     protected Map JavaDoc objectTable = new HashMap JavaDoc();
73
74     /**
75      * Timeout of the cached objects.
76      */
77     private long timeout = 1000 * 60 * 15;
78
79     /**
80      *
81      */
82     public ObjectCacheLocalDefaultImpl(PersistenceBroker broker, Properties JavaDoc prop)
83     {
84         timeout = prop == null ? timeout : ( Long.parseLong( prop.getProperty( TIMEOUT, "" + timeout ) ) )*1000;
85     }
86
87     /**
88      * Clear ObjectCache. I.e. remove all entries for classes and objects.
89      */
90     public void clear()
91     {
92         objectTable.clear();
93     }
94
95     /**
96      * Makes object persistent to the Objectcache.
97      * I'm using soft-references to allow gc reclaim unused objects
98      * even if they are still cached.
99      */
100     public void cache(Identity oid, Object JavaDoc obj)
101     {
102         if ((obj != null))
103         {
104             SoftReference JavaDoc ref = new SoftReference JavaDoc(new CacheEntry(obj));
105             objectTable.put(oid, ref);
106         }
107     }
108
109     public boolean cacheIfNew(Identity oid, Object JavaDoc obj)
110     {
111         if(objectTable.get(oid) == null)
112         {
113             cache(oid, obj);
114             return true;
115         }
116         return false;
117     }
118
119     /**
120      * Lookup object with Identity oid in objectTable.
121      * Returns null if no matching id is found
122      */
123     public Object JavaDoc lookup(Identity oid)
124     {
125         CacheEntry entry = null;
126         SoftReference JavaDoc ref = (SoftReference JavaDoc) objectTable.get(oid);
127         if (ref != null)
128         {
129             entry = (CacheEntry) ref.get();
130             if (entry == null || entry.lifetime < System.currentTimeMillis())
131             {
132                 objectTable.remove(oid); // Soft-referenced Object reclaimed by GC
133 // timeout, so set null
134 entry = null;
135             }
136         }
137         return entry != null ? entry.object : null;
138     }
139
140     /**
141      * Removes an Object from the cache.
142      */
143     public void remove(Identity oid)
144     {
145         if (oid != null)
146         {
147             objectTable.remove(oid);
148         }
149     }
150
151     public String JavaDoc toString()
152     {
153         ToStringBuilder buf = new ToStringBuilder(this, ToStringStyle.DEFAULT_STYLE);
154         buf.append("Count of cached objects", objectTable.keySet().size());
155         return buf.toString();
156     }
157
158     //-----------------------------------------------------------
159 // inner class
160 //-----------------------------------------------------------
161 class CacheEntry
162     {
163         long lifetime;
164         Object JavaDoc object;
165
166         public CacheEntry(Object JavaDoc object)
167         {
168             this.object = object;
169             lifetime = System.currentTimeMillis() + timeout;
170         }
171     }
172
173 }
174
Popular Tags