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;
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 singletonClassName = null;
26
27 private ThreadLocal perThreadCache = new ThreadLocal();
28
29 public PerThreadSingleton() {
30 }
31
32 public void reset() {
33 perThreadCache = new ThreadLocal();
34 }
35
36 public Object instance() {
37 Object singletonInstancePerThread = null;
38 // use weak reference to prevent cyclic reference during GC
39 WeakReference ref = (WeakReference) perThreadCache.get();
40 // singletonInstancePerThread=perThreadCache.get();
41 // if (singletonInstancePerThread==null) {
42 if (ref == null || ref.get() == null) {
43 Class clazz = null;
44 try {
45 clazz = Thread.currentThread().getContextClassLoader().loadClass(
46 singletonClassName);
47 singletonInstancePerThread = clazz.newInstance();
48 } catch (Exception ignore) {
49 try {
50 clazz = Class.forName(singletonClassName);
51 singletonInstancePerThread = clazz.newInstance();
52 } catch (Exception ignore2) {
53 }
54 }
55 perThreadCache.set(new WeakReference(singletonInstancePerThread));
56 } else {
57 singletonInstancePerThread = ref.get();
58 }
59 return singletonInstancePerThread;
60 }
61
62 public void setSingletonClassName(String 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 */