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JCommon is a free general purpose Java class library that is used in several projects at www.jfree.org, including JFreeChart and JFreeReport.
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/* ========================================================================
 * JCommon : a free general purpose class library for the Java(tm) platform
 * ========================================================================
 *
 * (C) Copyright 2000-2008, by Object Refinery Limited and Contributors.
 *
 * Project Info:  http://www.jfree.org/jcommon/index.html
 *
 * This library 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 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library 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 this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
 * USA.
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
 * in the United States and other countries.]
 *
 * --------------------------
 * ResourceBundleWrapper.java
 * --------------------------
 * (C)opyright 2008, by Jess Thrysoee and Contributors.
 *
 * Original Author:  Jess Thrysoee;
 * Contributor(s):   David Gilbert (for Object Refinery Limited);
 *
 * Changes
 * -------
 * 18-Dec-2008 : Version 1 (JT);
 *
 */

package org.jfree.util;

import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;
import java.util.ResourceBundle;

/**
 * Wrapper of ResourceBundle.getBundle() methods. This wrapper is introduced to
 * avoid a dramatic performance penalty by superfluous resource (and classes
 * loaded by Class.forName) lookups on web server in applets.
 *
 *  * public class AppletC extends javax.swing.JApplet {
 *    public void init() {
 *       ResourceBundleWrapper.removeCodeBase(getCodeBase(),
 *               (URLClassLoader) getClass().getClassLoader());
 *    ...
 * 
 *
 * @see 
 *               Bug ID: 4243379
 * @see 
 *               Bug ID: 4668479
 *
 * @since 1.0.15
 */
public class ResourceBundleWrapper {

    /**
     * A special class loader with no code base lookup.  This field may be
     * null (the field is only initialised if removeCodeBase() is
     * called from an applet.
     */
    private static URLClassLoader noCodeBaseClassLoader;

    /**
     * Private constructor.
     */
    private ResourceBundleWrapper() {
        // all methods are static, no need to instantiate
    }

    /**
     * Instantiate a {@link URLClassLoader} for resource lookups where the
     * codeBase URL is removed.  This method is typically called from an
     * applet's init() method.  If this method is never called, the
     * getBundle() methods map to the standard
     * {@link ResourceBundle} lookup methods.
     *
     * @param codeBase  the codeBase URL.
     * @param urlClassLoader  the class loader.
     */
    public static void removeCodeBase(URL codeBase,
            URLClassLoader urlClassLoader) {
        List urlsNoBase = new ArrayList();

        URL[] urls = urlClassLoader.getURLs();
        for (int i = 0; i < urls.length; i++) {
            if (! urls[i].sameFile(codeBase)) {
                urlsNoBase.add(urls[i]);
            }
        }
        // substitute the filtered URL list
        URL[] urlsNoBaseArray = (URL[]) urlsNoBase.toArray(new URL[0]);
        noCodeBaseClassLoader = URLClassLoader.newInstance(urlsNoBaseArray);
    }

    /**
     * Finds and returns the specified resource bundle.
     *
     * @param baseName  the base name.
     *
     * @return The resource bundle.
     */
    public static final ResourceBundle getBundle(String baseName) {
        // the noCodeBaseClassLoader is configured by a call to the
        // removeCodeBase() method, typically in the init() method of an
        // applet...
        if (noCodeBaseClassLoader != null) {
            return ResourceBundle.getBundle(baseName, Locale.getDefault(),
                    noCodeBaseClassLoader);
        }
        else {
            // standard ResourceBundle behaviour
            return ResourceBundle.getBundle(baseName);
        }
    }

    /**
     * Finds and returns the specified resource bundle.
     *
     * @param baseName  the base name.
     * @param locale  the locale.
     *
     * @return The resource bundle.
     */
    public static final ResourceBundle getBundle(String baseName,
            Locale locale) {

        // the noCodeBaseClassLoader is configured by a call to the
        // removeCodeBase() method, typically in the init() method of an
        // applet...
        if (noCodeBaseClassLoader != null) {
            return ResourceBundle.getBundle(baseName, locale,
                    noCodeBaseClassLoader);
        }
        else {
            // standard ResourceBundle behaviour
            return ResourceBundle.getBundle(baseName, locale);
        }
    }

    /**
     * Maps directly to ResourceBundle.getBundle(baseName, locale,
     * loader).
     *
     * @param baseName  the base name.
     * @param locale  the locale.
     * @param loader  the class loader.
     *
     * @return The resource bundle.
     */
    public static ResourceBundle getBundle(String baseName, Locale locale,
            ClassLoader loader) {
        return ResourceBundle.getBundle(baseName, locale, loader);
    }

}