/*
* JasperReports - Free Java Reporting Library.
* Copyright (C) 2001 - 2009 Jaspersoft Corporation. All rights reserved.
* http://www.jaspersoft.com
*
* Unless you have purchased a commercial license agreement from Jaspersoft,
* the following license terms apply:
*
* This program is part of JasperReports.
*
* JasperReports is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* JasperReports is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with JasperReports. If not, see <http://www.gnu.org/licenses/>.
*/
package net.sf.jasperreports.engine.util;
import java.util.Map;
import net.sf.jasperreports.engine.JRException;
import org.apache.commons.collections.ReferenceMap;
/**
* Utility to use as a soft cache of singleton instances.
*
* @author Lucian Chirita (lucianc@users.sourceforge.net)
* @version $Id: JRSingletonCache.java 3034 2009-08-27 11:58:04Z teodord $
*/
public class JRSingletonCache
{
private static final Object CONTEXT_KEY_NULL = new Object();
private final ReferenceMap cache;
private final Class itf;
/**
* Creates a cache of singleton instances.
*
* @param itf a interface or class that should be implemented by all classes cached by this object
*/
public JRSingletonCache(Class itf)
{
cache = new ReferenceMap(ReferenceMap.WEAK, ReferenceMap.SOFT);
this.itf = itf;
}
/**
* Returns the singleton instance corresponding to a class.
* <p>
* The instance is first searched into the cache and created if not found.
* <p>
* The class is expected to have a no-argument constructor.
*
* @param className
* @return the singleton instance corresponding to a class
* @throws JRException
*/
public synchronized Object getCachedInstance(String className) throws JRException
{
Map contextCache = getContextInstanceCache();
Object instance = contextCache.get(className);
if (instance == null)
{
instance = createInstance(className);
contextCache.put(className, instance);
}
return instance;
}
protected Object createInstance(String className) throws JRException
{
try
{
Class clazz = JRClassLoader.loadClassForName(className);
if (itf != null && !itf.isAssignableFrom(clazz))
{
throw new JRException("Class \"" + className + "\" should be compatible with \"" + itf.getName() + "\"");
}
return clazz.newInstance();
}
catch (ClassNotFoundException e)
{
throw new JRException("Class " + className + " not found.", e);
}
catch (InstantiationException e)
{
throw new JRException("Error instantiating class " + className + ".", e);
}
catch (IllegalAccessException e)
{
throw new JRException("Error instantiating class " + className + ".", e);
}
}
protected Map getContextInstanceCache()
{
Object contextKey = getContextKey();
Map contextCache = (Map) cache.get(contextKey);
if (contextCache == null)
{
contextCache = new ReferenceMap();
cache.put(contextKey, contextCache);
}
return contextCache;
}
protected Object getContextKey()
{
Object key = Thread.currentThread().getContextClassLoader();
if (key == null)
{
key = CONTEXT_KEY_NULL;
}
return key;
}
}