com.inamik.template.util.ClassLoaderUtil.java Source code

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Here is the source code for com.inamik.template.util.ClassLoaderUtil.java

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/*
 * $Id: ClassLoaderUtil.java,v 1.3 2006-08-21 03:07:12 dave Exp $
 *
 * iNamik Template Engine
 * Copyright (C) 2006 David Farrell (davidpfarrell@yahoo.com)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
package com.inamik.template.util;

import java.io.InputStream;
import java.net.URL;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * ClassLoaderUtil - Utility class for dealing with classloaders and resources
 * on the classpath.
 * <p>
 * Borrowed ideas found in EHCACHE
 * <p>
 * Created on Jul 30, 2006
 * @author Dave
 */
public final class ClassLoaderUtil {
    private static final Log LOG = LogFactory.getLog(ClassLoaderUtil.class.getName());

    /**
     * Constructor
     */
    private ClassLoaderUtil() {
    }

    /**
     * getStandardClassLoader - Get the current thread's ClassLoader.
     *
     * @return The current thread's ClassLoader
     */
    public static ClassLoader getStandardClassLoader() {
        return Thread.currentThread().getContextClassLoader();
    }

    /**
     * getLocalClassLoader - Get the ClassLoader for this class
     * (ClassLoaderUtil).
     *
     * @return The ClassLoader for ClassLoaderUtil
     */
    public static ClassLoader getLocalClassLoader() {
        return ClassLoaderUtil.class.getClassLoader();
    }

    /**
     * getResourceAsStream - Try to find a resource on the classpath and
     * return a stream to the found resource.
     * <p>
     * This method first checks the standard class loader.  If that fails,
     * it then checks the local class loader.
     * <p>
     * It is up to the caller to close the stream.
     *
     * @param resource The resource to find on the classpath.
     *
     * @return A stream to the classpath resource, or <code>null</code>
     *         if the resource was not found.
     *
     * @see #getStandardClassLoader()
     * @see #getLocalClassLoader()
     */
    public static InputStream getResourceAsStream(final String resource) {
        if (resource == null) {
            throw new NullPointerException("resource");
        }

        InputStream stream = getStandardClassLoader().getResourceAsStream(resource);

        if (stream == null) {
            stream = getLocalClassLoader().getResourceAsStream(resource);
        }

        if (stream == null) {
            if (LOG.isInfoEnabled())
                LOG.info("Unable to find resource '" + resource + "'");
        }

        return stream;
    }

    /**
     * getResourceAsURL - Try to find a resource on the classpath and
     * return a URL to the found resource.
     * <p>
     * This method first checks the standard class loader.  If that fails,
     * it then checks the local class loader.
     *
     * @param resource The resource to find on the classpath.
     *
     * @return A URL to the classpath resource, or <code>null</code>
     *         if the resource was not found.
     *
     * @see #getStandardClassLoader()
     * @see #getLocalClassLoader()
     */
    public static URL getResourceAsURL(final String resource) {
        if (resource == null) {
            throw new NullPointerException("resource");
        }

        URL url = getStandardClassLoader().getResource(resource);

        if (url == null) {
            url = getLocalClassLoader().getResource(resource);
        }

        if (url == null) {
            if (LOG.isInfoEnabled())
                LOG.info("Unable to find resource '" + resource + "'");
        }

        return url;
    }

    /**
     * createNewInstance - Create a new instance of the specified class.
     * <p>
     * This method first tries to create the new instance using the standard
     * class loader.  If that fails, it then tries using the local class
     * loader.
     *
     * @param className The name of the class to instantiate.
     * @return New instance of the specified class, or null if the class could
     *         not be found or instantiated.
     *
     * @see #getStandardClassLoader()
     * @see #getLocalClassLoader()
     */
    public static Object createNewInstance(final String className) {
        if (className == null) {
            throw new NullPointerException("className");
        }

        Class clazz;

        Object newInstance;

        try {
            clazz = Class.forName(className, true, getStandardClassLoader());
        } catch (ClassNotFoundException e) {
            try {
                clazz = Class.forName(className, true, getLocalClassLoader());
            } catch (ClassNotFoundException ex) {
                if (LOG.isWarnEnabled())
                    LOG.warn("Unable to find class '" + className + "'");

                return null;
            }
        }

        try {
            newInstance = clazz.newInstance();
        } catch (IllegalAccessException e) {
            if (LOG.isWarnEnabled())
                LOG.warn("Unable to load class '" + className + "'. Cause was " + e.getMessage(), e);

            return null;
        } catch (InstantiationException e) {
            if (LOG.isWarnEnabled())
                LOG.warn("Unable to load class '" + className + "'. Cause was " + e.getMessage(), e);

            return null;
        }

        return newInstance;
    }
}