org.harmony.server.startup.ResourceLoader.java Source code

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Here is the source code for org.harmony.server.startup.ResourceLoader.java

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/*
 * Copyright 1999-2005 The Apache Software Foundation.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.harmony.server.startup;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URL;

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

/**
 * Load resources (or images) from various sources.
 * 
 * @author Ceki Gülcü
 * 
 *         (Very small adaptations by Michael Meyling and Amir Arad.)
 */

public class ResourceLoader {

    static final String TSTR = "Caught Exception while in Loader.getResource. This may be innocuous.";

    /** Trace logger. */
    private static Log trace = LogFactory.getLog(ResourceLoader.class);

    // We conservatively assume that we are running under Java 1.x
    static private boolean java1 = true;

    static private boolean ignoreTCL = false;

    static {
        final String prop = System.getProperty("java.version", null);

        if (prop != null) {
            final int i = prop.indexOf('.');
            if (i != -1) {
                if (prop.charAt(i + 1) != '1') {
                    java1 = false;
                }
            }
        }
        final String ignoreTCLProp = System.getProperty("log4j.ignoreTCL", null);
        if (ignoreTCLProp != null) {
            ignoreTCL = toBoolean(ignoreTCLProp, true);
        }
    }

    /**
     * This method will search for <code>resource</code> in different places.
     * The search order is as follows:
     * 
     * <ol>
     * 
     * <p>
     * <li>Search for <code>resource</code> using the thread context class
     * loader under Java2. If that fails, search for <code>resource</code> using
     * the class loader that loaded this class (<code>Loader</code>). Under JDK
     * 1.1, only the the class loader that loaded this class (
     * <code>Loader</code>) is used.
     * 
     * <p>
     * <li>Try one last time with
     * <code>ClassLoader.getSystemResource(resource)</code>, that is is using
     * the system class loader in JDK 1.2 and virtual machine's built-in class
     * loader in JDK 1.1.
     * 
     * </ol>
     */
    static public URL getResource(final String resource) {
        ClassLoader classLoader = null;
        URL url = null;

        try {
            if (!java1) {
                classLoader = getTCL();
                if (classLoader != null) {
                    trace.debug("Trying to find [" + resource + "] using context classloader " + classLoader + ".");
                    url = classLoader.getResource(resource);
                    if (url != null)
                        return url;
                }
            }

            // We could not find resource. Ler us now try with the
            // classloader that loaded this class.
            classLoader = ResourceLoader.class.getClassLoader();
            if (classLoader != null) {
                trace.debug("Trying to find [" + resource + "] using " + classLoader + " class loader.");
                url = classLoader.getResource(resource);
                if (url != null)
                    return url;
            }
        } catch (final Throwable t) {
            trace.warn(TSTR, t);
        }

        // Last ditch attempt: get the resource from the class path. It
        // may be the case that clazz was loaded by the Extentsion class
        // loader which the parent of the system class loader. Hence the
        // code below.
        trace.debug("Trying to find [" + resource + "] using ClassLoader.getSystemResource().");
        return ClassLoader.getSystemResource(resource);
    }

    /**
     * Are we running under JDK 1.x?
     */
    public static boolean isJava1() {
        return java1;
    }

    /**
     * Get the Thread Context Loader which is a JDK 1.2 feature. If we are
     * running under JDK 1.1 or anything else goes wrong the method returns
     * <code>null<code>.
     * 
     * */
    private static ClassLoader getTCL() throws IllegalAccessException, InvocationTargetException {

        // Are we running on a JDK 1.2 or later system?
        Method method = null;
        try {
            method = Thread.class.getMethod("getContextClassLoader");
        } catch (final NoSuchMethodException e) {
            // We are running on JDK 1.1
            return null;
        }

        return (ClassLoader) method.invoke(Thread.currentThread());
    }

    /**
     * If running under JDK 1.2 load the specified class using the
     * <code>Thread</code> <code>contextClassLoader</code> if that fails try
     * Class.forname. Under JDK 1.1 only Class.forName is used.
     * 
     */
    static public Class<?> loadClass(final String clazz) throws ClassNotFoundException {
        // Just call Class.forName(clazz) if we are running under JDK 1.1
        // or if we are instructed to ignore the TCL.
        if (java1 || ignoreTCL)
            return Class.forName(clazz);
        else {
            try {
                return getTCL().loadClass(clazz);
            } catch (final Throwable e) {
                // we reached here because tcl was null or because of a
                // security exception, or because clazz could not be loaded...
                // In any case we now try one more time
                return Class.forName(clazz);
            }
        }
    }

    /**
     * If <code>value</code> is "true", then <code>true</code> is returned. If
     * <code>value</code> is "false", then <code>true</code> is returned.
     * Otherwise, <code>default</code> is returned.
     * 
     * <p>
     * Case of value is unimportant.
     */
    public static boolean toBoolean(final String value, final boolean dEfault) {
        if (value == null)
            return dEfault;
        final String trimmedVal = value.trim();
        if ("true".equalsIgnoreCase(trimmedVal))
            return true;
        if ("false".equalsIgnoreCase(trimmedVal))
            return false;
        return dEfault;
    }

}