Logback: the reliable, generic, fast and flexible logging framework.
Copyright (C) 1999-2015, QOS.ch. All rights reserved.
This program and the accompanying materials are dual-licensed under
either the terms of the Eclipse Public License v1.0 as published by
the Eclipse Foundation
  or (per the licensee's choosing)
under the terms of the GNU Lesser General Public License version 2.1
as published by the Free Software Foundation.
/**
 * Logback: the reliable, generic, fast and flexible logging framework.
 * Copyright (C) 1999-2015, QOS.ch. All rights reserved.
 *
 * This program and the accompanying materials are dual-licensed under
 * either the terms of the Eclipse Public License v1.0 as published by
 * the Eclipse Foundation
 *
 *   or (per the licensee's choosing)
 *
 * under the terms of the GNU Lesser General Public License version 2.1
 * as published by the Free Software Foundation.
 */
package ch.qos.logback.core.util;

import java.io.IOException;
import java.net.URL;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Enumeration;
import java.util.Set;
import java.util.HashSet;

import ch.qos.logback.core.Context;

Load resources (or images) from various sources.
Author:
Ceki Gülcü/**
 * Load resources (or images) from various sources.
 *
 * @author Ceki Gülcü
 */
public class Loader {
    static final String TSTR = "Caught Exception while in Loader.getResource. This may be innocuous.";

    private static boolean ignoreTCL = false;
    public static final String IGNORE_TCL_PROPERTY_NAME = "logback.ignoreTCL";
    private static boolean HAS_GET_CLASS_LOADER_PERMISSION = false;

    static {
        String ignoreTCLProp = OptionHelper.getSystemProperty(IGNORE_TCL_PROPERTY_NAME, null);

        if (ignoreTCLProp != null) {
            ignoreTCL = OptionHelper.toBoolean(ignoreTCLProp, true);
        }

        HAS_GET_CLASS_LOADER_PERMISSION = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
            public Boolean run() {
                try {
                    AccessController.checkPermission(new RuntimePermission("getClassLoader"));
                    return true;
                } catch (SecurityException e) {
                    // Using SecurityException instead of AccessControlException.
                    // See bug LOGBACK-760.
                    return false;
                }
            }
        });
    }

    
Compute the number of occurrences a resource can be found by a class
loader.
Params:
resource – 
classLoader – 
Throws:
IOException – 
Returns:
/**
     * Compute the number of occurrences a resource can be found by a class
     * loader.
     *
     * @param resource
     * @param classLoader
     * @return

     * @throws IOException
     */

    public static Set<URL> getResources(String resource, ClassLoader classLoader) throws IOException {
        // See LBCLASSIC-159
        Set<URL> urlSet = new HashSet<URL>();
        Enumeration<URL> urlEnum = classLoader.getResources(resource);
        while (urlEnum.hasMoreElements()) {
            URL url = urlEnum.nextElement();
            urlSet.add(url);
        }
        return urlSet;
    }

    
Search for a resource using the classloader passed as parameter.
Params:
resource –    the resource name to look for
classLoader – the classloader used for the search/**
     * Search for a resource using the classloader passed as parameter.
     *
     * @param resource    the resource name to look for
     * @param classLoader the classloader used for the search
     */
    public static URL getResource(String resource, ClassLoader classLoader) {
        try {
            return classLoader.getResource(resource);
        } catch (Throwable t) {
            return null;
        }
    }

    
Attempt to find a resource by using the classloader that loaded this class,
namely Loader.class.
Params:
resource – 
Returns:
/**
     * Attempt to find a resource by using the classloader that loaded this class,
     * namely Loader.class.
     *
     * @param resource
     * @return

     */
    public static URL getResourceBySelfClassLoader(String resource) {
        return getResource(resource, getClassLoaderOfClass(Loader.class));
    }

    // private static URL getResourceByTCL(String resource) {
    // return getResource(resource, getTCL());
    // }

    
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
null.
/**
     * 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>.
     */
    public static ClassLoader getTCL() {
        return Thread.currentThread().getContextClassLoader();
    }

    public static Class<?> loadClass(String clazz, Context context) throws ClassNotFoundException {
        ClassLoader cl = getClassLoaderOfObject(context);
        return cl.loadClass(clazz);
    }

    
Get the class loader of the object passed as argument. Return the system
class loader if appropriate.
Params:
o – 
Returns:
/**
     * Get the class loader of the object passed as argument. Return the system
     * class loader if appropriate.
     *
     * @param o
     * @return

     */
    public static ClassLoader getClassLoaderOfObject(Object o) {
        if (o == null) {
            throw new NullPointerException("Argument cannot be null");
        }
        return getClassLoaderOfClass(o.getClass());
    }

    
Returns the class loader of clazz in an access privileged section.
Params:
clazz – 
Returns:
/**
     * Returns the class loader of clazz in an access privileged section.
     *
     * @param clazz
     * @return

     */
    public static ClassLoader getClassLoaderAsPrivileged(final Class<?> clazz) {
        if (!HAS_GET_CLASS_LOADER_PERMISSION)
            return null;
        else
            return AccessController.doPrivileged(new PrivilegedAction<ClassLoader>() {
                public ClassLoader run() {
                    return clazz.getClassLoader();
                }
            });
    }

    
Return the class loader which loaded the class passed as argument. Return
the system class loader if appropriate.
Params:
clazz – 
Returns:
/**
     * Return the class loader which loaded the class passed as argument. Return
     * the system class loader if appropriate.
     *
     * @param clazz
     * @return

     */
    public static ClassLoader getClassLoaderOfClass(final Class<?> clazz) {
        ClassLoader cl = clazz.getClassLoader();
        if (cl == null) {
            return ClassLoader.getSystemClassLoader();
        } else {
            return cl;
        }
    }

    
If running under JDK 1.2 load the specified class using the
Thread contextClassLoader if that fails try
Class.forname. Under JDK 1.1 only Class.forName is used.
/**
     * 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.
     */
    public static Class<?> loadClass(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 (ignoreTCL) {
            return Class.forName(clazz);
        } else {
            try {
                return getTCL().loadClass(clazz);
            } catch (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);
            }
        }
    }
}