/*
 * Copyright 2008 The Depan Project Authors
 *
 * 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 com.google.devtools.depan.platform.plugin;

import org.osgi.framework.Bundle;

import java.util.Collection;

/**
 * A ClassLoader that can load classes provided by source plugin.
 * It is used by XStream to find the classes when deserializing objects.
 *
 * @author Yohann Coppel
 *
 */
public class PluginClassLoader extends ClassLoader {

  /**
   * List of bundles for each plugin. Used to load the classes.
   */
  private final Collection<Bundle> pluginBundles;

  /**
   * Construct the class loader. Get and save the {@link Bundle}s for each
   * plugin.
   *
   * @param collection
   */
  public PluginClassLoader(Collection<Bundle> pluginBundles) {
    this.pluginBundles = pluginBundles;
  }

  /**
   * Try to load classes from the known list of bundles, in order.
   * If all of those fail, delegate to the super class.
   */
  @Override
  public Class<?> loadClass(String name) throws ClassNotFoundException {
    for (Bundle bundle: pluginBundles) {
      // try to load the class one plugin after the other. stop on the first
      // plugin providing the corresponding class.
      try {
        return bundle.loadClass(name);
      } catch (ClassNotFoundException e) {
      }
    }
    return super.loadClass(name);
  }
}