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TrueZIP is a Java based Virtual File System (VFS) to enable transparent, multi-threaded read/write access to archive files (ZIP, TAR etc.) as if they were directories. Archive files may be arbitrarily nested and the nesting level is only limited by heap and file system size.

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/*
 * Copyright (C) 2010 Schlichtherle IT Services
 *
 * 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 de.schlichtherle.util;

import java.io.IOException;
import java.util.Enumeration;

/**
 * Provides static utility methods for convenient class and resource loading
 * which is designed to work in both JEE and OSGi environments.
 * You cannot instantiate this class.
 *
 * @author Christian Schlichtherle
 * @version $Id$
 * @since TrueZIP 6.8
 * @deprecated This class is just a workaround until the introduction of a
 *             better, but probably non-backwards-compatible solution in
 *             TrueZIP 7. Do not use!
 */
public class ClassLoaders {

    ClassLoaders() {
    }

    /**
     * Tries to load the class {@code classToLoad} using the class loader of
     * the class {@code loadingClass} first or, failing that, using the
     * current thread's context class loader or, if not available, the system
     * class loader.
     *
     * @param classToLoad The class to load.
     * @param loadingClass The class which wants to load {@code classToLoad}.
     * @return The loaded class.
     * @throws ClassNotFoundException If loading the class failed for some
     *         reason.
     */
    public static Class loadClass(String classToLoad, Class loadingClass)
    throws ClassNotFoundException {
        ClassLoader l1 = loadingClass.getClassLoader();
        if (l1 == null)
            l1 = ClassLoader.getSystemClassLoader(); // just in case somebody adds TrueZIP to the Boot Class Path
        try {
            return l1.loadClass(classToLoad);
        } catch (ClassNotFoundException cnfe) {
            ClassLoader l2 = Thread.currentThread().getContextClassLoader();
            if (l2 == null)
                l2 = ClassLoader.getSystemClassLoader();
            if (l1 == l2)
                throw cnfe; // optimization: there's no point in trying this twice.
            return l2.loadClass(classToLoad);
        }
    }

    /**
     * Concatenates the enumeration of the resource {@code name} on the class
     * path by using the class loader of the class {@code loadingClass} and the
     * current thread's context class loader or, if not available, the system
     * class loader.
     *
     * @param name The resource to enumerate.
     * @param loadingClass The class which wants to enumerate {@code name}.
     * @return A joint enumeration for the resource {@code name} on the class
     *         path.
     * @throws IOException If I/O errors occur.
     */
    public static Enumeration getResources(String name, Class loadingClass)
    throws IOException {
        ClassLoader l1 = loadingClass.getClassLoader();
        if (l1 == null)
            l1 = ClassLoader.getSystemClassLoader(); // just in case somebody adds TrueZIP to the Boot Class Path
        ClassLoader l2 = Thread.currentThread().getContextClassLoader();
        if (l2 == null)
            l2 = ClassLoader.getSystemClassLoader();
        return l1 == l2
                ? l1.getResources(name)
                : new JointEnumeration( l1.getResources(name),
                                        l2.getResources(name));
    }
}