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Java > Open Source Codes > org > dom4j > util > PerThreadSingleton


1 /*
2  * Copyright 2001-2005 (C) MetaStuff, Ltd. All Rights Reserved.
3  *
4  * This software is open source.
5  * See the bottom of this file for the licence.
6  */
7
8 package org.dom4j.util;
9
10 import java.lang.ref.WeakReference JavaDoc;
11
12 /**
13  * <p>
14  * <code>PerThreadSingleton</code> is an implementation of the
15  * SingletonStrategy used to provide common factory access to a single object
16  * instance based on an implementation strategy for one object instance per
17  * thread. This is useful in replace of the ThreadLocal usage.
18  * </p>
19  *
20  * @author <a HREF="mailto:ddlucas@users.sourceforge.net">David Lucas </a>
21  * @version $Revision: 1.3 $
22  */
23
24 public class PerThreadSingleton implements SingletonStrategy {
25     private String JavaDoc singletonClassName = null;
26
27     private ThreadLocal JavaDoc perThreadCache = new ThreadLocal JavaDoc();
28
29     public PerThreadSingleton() {
30     }
31
32     public void reset() {
33         perThreadCache = new ThreadLocal JavaDoc();
34     }
35
36     public Object JavaDoc instance() {
37         Object JavaDoc singletonInstancePerThread = null;
38         // use weak reference to prevent cyclic reference during GC
39 WeakReference JavaDoc ref = (WeakReference JavaDoc) perThreadCache.get();
40         // singletonInstancePerThread=perThreadCache.get();
41 // if (singletonInstancePerThread==null) {
42 if (ref == null || ref.get() == null) {
43             Class JavaDoc clazz = null;
44             try {
45                 clazz = Thread.currentThread().getContextClassLoader().loadClass(
46                         singletonClassName);
47                 singletonInstancePerThread = clazz.newInstance();
48             } catch (Exception JavaDoc ignore) {
49                 try {
50                     clazz = Class.forName(singletonClassName);
51                     singletonInstancePerThread = clazz.newInstance();
52                 } catch (Exception JavaDoc ignore2) {
53                 }
54             }
55             perThreadCache.set(new WeakReference JavaDoc(singletonInstancePerThread));
56         } else {
57             singletonInstancePerThread = ref.get();
58         }
59         return singletonInstancePerThread;
60     }
61
62     public void setSingletonClassName(String JavaDoc singletonClassName) {
63         this.singletonClassName = singletonClassName;
64     }
65
66 }
67
68 /*
69  * Redistribution and use of this software and associated documentation
70  * ("Software"), with or without modification, are permitted provided that the
71  * following conditions are met:
72  *
73  * 1. Redistributions of source code must retain copyright statements and
74  * notices. Redistributions must also contain a copy of this document.
75  *
76  * 2. Redistributions in binary form must reproduce the above copyright notice,
77  * this list of conditions and the following disclaimer in the documentation
78  * and/or other materials provided with the distribution.
79  *
80  * 3. The name "DOM4J" must not be used to endorse or promote products derived
81  * from this Software without prior written permission of MetaStuff, Ltd. For
82  * written permission, please contact dom4j-info@metastuff.com.
83  *
84  * 4. Products derived from this Software may not be called "DOM4J" nor may
85  * "DOM4J" appear in their names without prior written permission of MetaStuff,
86  * Ltd. DOM4J is a registered trademark of MetaStuff, Ltd.
87  *
88  * 5. Due credit should be given to the DOM4J Project - http://www.dom4j.org
89  *
90  * THIS SOFTWARE IS PROVIDED BY METASTUFF, LTD. AND CONTRIBUTORS ``AS IS'' AND
91  * ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
92  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
93  * ARE DISCLAIMED. IN NO EVENT SHALL METASTUFF, LTD. OR ITS CONTRIBUTORS BE
94  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
95  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
96  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
97  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
98  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
99  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
100  * POSSIBILITY OF SUCH DAMAGE.
101  *
102  * Copyright 2001-2005 (C) MetaStuff, Ltd. All Rights Reserved.
103  */
104
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