ch.qos.cal10n.plugins.ThisFirstClassLoader Maven / Gradle / Ivy

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/*
 * Copyright (c) 2009 QOS.ch All rights reserved.
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS  IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package ch.qos.cal10n.plugins;

import java.net.URL;
import java.net.URLClassLoader;

/**
 * An almost trivial no fuss implementation of a class loader following the
 * child-first delegation model.
 * 
 * @author Ceki G?lc?
 */
public class ThisFirstClassLoader extends URLClassLoader {

  public ThisFirstClassLoader(URL[] urls) {
    super(urls);
  }

  public ThisFirstClassLoader(URL[] urls, ClassLoader parent) {
    super(urls, parent);
  }

  public void addURL(URL url) {
    super.addURL(url);
  }

  @Override
  public Class loadClass(String name) throws ClassNotFoundException {
    return loadClass(name, false);
  }

  /**
   * We override the parent-first behavior established by java.lang.Classloader.
   * 
   * The implementation is surprisingly straightforward.
   */
  protected Class loadClass(String name, boolean resolve)
      throws ClassNotFoundException {

    // Treating IMessageKeyVerifier as a special case is the whole point of the
    // exercise.
    if (name.equals("ch.qos.cal10n.verifier.IMessageKeyVerifier")) {
      return super.loadClass(name, resolve);
    }

    // First, check if the class has already been loaded
    Class c = findLoadedClass(name);

    // if not loaded, search the local (child) resources
    if (c == null) {
      try {
        c = findClass(name);
      } catch (ClassNotFoundException cnfe) {
        // ignore
      }
    }

    // if we could not find it, delegate to parent
    // Note that we don't attempt to catch any ClassNotFoundException
    if (c == null) {
      if (getParent() != null) {
        c = getParent().loadClass(name);
      } else {
        c = getSystemClassLoader().loadClass(name);
      }
    }

    if (resolve) {
      resolveClass(c);
    }

    return c;
  }
}