01: /*
02: * ============================================================================
03: * GNU Lesser General Public License
04: * ============================================================================
05: *
06: * JasperReports - Free Java report-generating library.
07: * Copyright (C) 2001-2006 JasperSoft Corporation http://www.jaspersoft.com
08: *
09: * This library is free software; you can redistribute it and/or
10: * modify it under the terms of the GNU Lesser General Public
11: * License as published by the Free Software Foundation; either
12: * version 2.1 of the License, or (at your option) any later version.
13: *
14: * This library is distributed in the hope that it will be useful,
15: * but WITHOUT ANY WARRANTY; without even the implied warranty of
16: * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17: * Lesser General Public License for more details.
18: *
19: * You should have received a copy of the GNU Lesser General Public
20: * License along with this library; if not, write to the Free Software
21: * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
22: *
23: * JasperSoft Corporation
24: * 303 Second Street, Suite 450 North
25: * San Francisco, CA 94107
26: * http://www.jaspersoft.com
27: */
28: package net.sf.jasperreports.engine.util;
29:
30: import net.sf.jasperreports.engine.JRException;
31:
32: import org.apache.commons.collections.ReferenceMap;
33:
34: /**
35: * Utility to use as a soft cache of singleton instances.
36: *
37: * @author Lucian Chirita (lucianc@users.sourceforge.net)
38: * @version $Id: JRSingletonCache.java 1245 2006-04-28 08:23:04Z lucianc $
39: */
40: public class JRSingletonCache {
41: private final ReferenceMap cache;
42: private final Class itf;
43:
44: /**
45: * Creates a cache of singleton instances.
46: *
47: * @param itf a interface or class that should be implemented by all classes cached by this object
48: */
49: public JRSingletonCache(Class itf) {
50: cache = new ReferenceMap();
51: this .itf = itf;
52: }
53:
54: /**
55: * Returns the singleton instance corresponding to a class.
56: * <p>
57: * The instance is first searched into the cache and created if not found.
58: * <p>
59: * The class is expected to have a no-argument constructor.
60: *
61: * @param className
62: * @return the singleton instance corresponding to a class
63: * @throws JRException
64: */
65: public synchronized Object getCachedInstance(String className)
66: throws JRException {
67: Object instance = cache.get(className);
68: if (instance == null) {
69: try {
70: Class clazz = JRClassLoader.loadClassForName(className);
71: if (itf != null && !itf.isAssignableFrom(clazz)) {
72: throw new JRException("Class \"" + className
73: + "\" should be compatible with \""
74: + itf.getName() + "\"");
75: }
76:
77: instance = clazz.newInstance();
78: } catch (ClassNotFoundException e) {
79: throw new JRException("Class " + className
80: + " not found.", e);
81: } catch (InstantiationException e) {
82: throw new JRException("Error instantiating class "
83: + className + ".", e);
84: } catch (IllegalAccessException e) {
85: throw new JRException("Error instantiating class "
86: + className + ".", e);
87: }
88:
89: cache.put(className, instance);
90: }
91: return instance;
92: }
93: }
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