RC9/qpid/java/junit-toolkit-maven-plugin/src/main/org/apache/qpid/junit/maven/IsolatedClassLoader.java

/*
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.qpid.junit.maven;

import java.net.URL;
import java.net.URLClassLoader;
import java.util.HashSet;
import java.util.Set;

/**
 * <p><table id="crc"><caption>CRC Card</caption>
 * <tr><th> Responsibilities <th> Collaborations
 * </table>
 *
 * @author Rupert Smith
 *
 * @noinspection CustomClassloader
 */
public class IsolatedClassLoader extends URLClassLoader
{

    private static final URL[] EMPTY_URL_ARRAY = new URL[0];
    private ClassLoader parent = ClassLoader.getSystemClassLoader();

    private Set urls = new HashSet();

    private boolean childDelegation = true;

    public IsolatedClassLoader()
    {
        super(EMPTY_URL_ARRAY, null);
    }

    public IsolatedClassLoader(ClassLoader parent, boolean childDelegation)
    {
        super(EMPTY_URL_ARRAY, parent);

        this.childDelegation = childDelegation;
    }

    public IsolatedClassLoader(ClassLoader parent)
    {
        super(EMPTY_URL_ARRAY, parent);
    }

    public void addURL(URL url)
    {
        // avoid duplicates
        if (!urls.contains(url))
        {
            super.addURL(url);
            urls.add(url);
        }
    }

    public synchronized Class loadClass(String name) throws ClassNotFoundException
    {
        Class c;

        if (childDelegation)
        {
            c = findLoadedClass(name);

            ClassNotFoundException ex = null;

            if (c == null)
            {
                try
                {
                    c = findClass(name);
                }
                catch (ClassNotFoundException e)
                {
                    ex = e;

                    if (parent != null)
                    {
                        c = parent.loadClass(name);
                    }
                }
            }

            if (c == null)
            {
                throw ex;
            }
        }
        else
        {
            c = super.loadClass(name);
        }

        return c;
    }
}