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Java unlimited runtime class and resource redefinition.

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/*
 * Copyright 2013-2024 the HotswapAgent authors.
 *
 * This file is part of HotswapAgent.
 *
 * HotswapAgent 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.
 *
 * HotswapAgent 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 HotswapAgent. If not, see http://www.gnu.org/licenses/.
 */
package org.hotswap.agent.plugin.proxy.hscglib;

import java.io.IOException;
import java.io.InputStream;
import org.hotswap.agent.plugin.proxy.ProxyTransformationUtils;

/**
 *
 * Tries to load classes by itself first. Tries the parent Classloader last.
 *
 * @author Erki Ehtla
 *
 */
public class ParentLastClassLoader extends ClassLoader {
    public static final String[] EXCLUDED_PACKAGES = new String[] { "java.", "javax.", "sun.", "oracle." };

    public ParentLastClassLoader(ClassLoader parent) {
        super(parent);
    }

    @Override
    protected Class loadClass(String name, boolean resolve) throws ClassNotFoundException {
        for (String excludedPackage : EXCLUDED_PACKAGES) {
            if (name.startsWith(excludedPackage))
                return super.loadClass(name, resolve);
        }
        Class clazz = loadClassFromThisClassLoader(name);
        if (clazz == null)
            return super.loadClass(name, resolve);

        if (resolve) {
            resolveClass(clazz);
        }
        return clazz;
    }

    protected Class loadClassFromThisClassLoader(String name) throws ClassNotFoundException {
        Class result = findLoadedClass(name);
        if (result != null) {
            return result;
        }
        byte[] bytes = readClass(name);
        if (bytes != null) {
            return defineClass(name, bytes, 0, bytes.length);
        }
        return null;
    }

    protected byte[] readClass(String name) throws ClassNotFoundException {
        InputStream is = getParent().getResourceAsStream(name.replace('.', '/') + ".class");
        if (is == null) {
            return null;
        }
        try {
            return ProxyTransformationUtils.copyToByteArray(is);
        } catch (IOException ex) {
            throw new ClassNotFoundException("Could not read: " + name, ex);
        }
    }
}