/*
 * Loader.java January 2010
 *
 * Copyright (C) 2010, Niall Gallagher <niallg@users.sf.net>
 *
 * 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 org.simpleframework.xml.strategy;

/**
 * The <code>Loader</code> object is used to provide class loading
 * for the strategies. This will attempt to load the class using
 * the thread context class loader, if this loader is set it will
 * be used to load the class. If not then the class will be loaded
 * using the caller class loader. Loading in this way ensures 
 * that a custom loader can be provided using the current thread.
 * 
 * @author Niall Gallagher
 */
class Loader {
   
   /**
    * This method is used to acquire the class of the specified name.
    * Loading is performed by the thread context class loader as this
    * will ensure that the class loading strategy can be changed as
    * requirements dictate. Typically the thread context class loader
    * can handle all serialization requirements.
    * 
    * @param type this is the name of the class that is to be loaded
    * 
    * @return this returns the class that has been loaded by this
    */
   public Class load(String type) throws Exception {
      ClassLoader loader = getClassLoader();
      
      if(loader == null) {
         loader = getCallerClassLoader();
      }
      return loader.loadClass(type);      
   }
   
   /**
    * This is used to acquire the caller class loader for this object.
    * Typically this is only used if the thread context class loader
    * is set to null. This ensures that there is at least some class
    * loader available to the strategy to load the class.
    * 
    * @return this returns the loader that loaded this class     
    */
   private static ClassLoader getCallerClassLoader() throws Exception {
      return Loader.class.getClassLoader();
   }

   /**
    * This is used to acquire the thread context class loader. This
    * is the default class loader used by the cycle strategy. When
    * using the thread context class loader the caller can switch the
    * class loader in use, which allows class loading customization.
    * 
    * @return this returns the loader used by the calling thread
    */
   private static ClassLoader getClassLoader() throws Exception {
      return Thread.currentThread().getContextClassLoader();
   }
   
}