src/org/apache/xml/serializer/Utils.java

/*
 * The Apache Software License, Version 1.1
 *
 *
 * Copyright (c) 2003 The Apache Software Foundation.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Xalan" and "Apache Software Foundation" must
 *    not be used to endorse or promote products derived from this
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 * 5. Products derived from this software may not be called "Apache",
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 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation and was
 * originally based on software copyright (c) 2003, International Business
 * Machines, Inc., http://www.ibm.com.  For more information on the Apache
 * Software Foundation, please see
 * <http://www.apache.org/>.
 */
package org.apache.xml.serializer;

import java.util.Hashtable;

/**
 * This class contains utilities used by the serializer
 */
class Utils
{

    /**
     * This nested class acts as a way to lazy load the hashtable
     * in a thread safe way.
     */
    static private class CacheHolder
    {
        static final Hashtable cache;
        static {
            cache = new Hashtable();
        }
    }
    /**
     * Load the class by name.
     * 
     * This implementation, for performance reasons,
     * caches all classes loaded by name and
     * returns the cached Class object if it can previously 
     * loaded classes that were load by name.  If not previously loaded
     * an attempt is made to load with Class.forName(classname)
     * @param classname the name of the class to be loaded
     * @return the loaded class, never null. If the class could not be
     * loaded a ClassNotFound exception is thrown.
     * @throws ClassNotFoundException if the class was not loaded
     */
    static Class ClassForName(String classname) throws ClassNotFoundException
    {
        Class c;
        // the first time the next line runs will reference
        // CacheHolder, causing the class to load and create the
        // Hashtable.
        Object o = CacheHolder.cache.get(classname);
        if (o == null)
        {
            // class was not in the cache, so try to load it
            c = Class.forName(classname);
            // if the class is not found we will have thrown a
            // ClassNotFoundException on the statement above
            
            // if we get here c is not null
            CacheHolder.cache.put(classname, c);
        }
        else
        {
            c = (Class)o;
        }
        return c;
    }
}