/**
    *    Copyright 2009-2015 the original author or 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 org.apache.ibatis.io;
  
  import java.io.InputStream;
  import java.net.URL;
  
  /**
   * A class to wrap access to multiple class loaders making them work as one
   *
   * @author Clinton Begin
   */
  public class ClassLoaderWrapper {
  
    ClassLoader defaultClassLoader;
    ClassLoader systemClassLoader;
  
    ClassLoaderWrapper() {
      try {
        systemClassLoader = ClassLoader.getSystemClassLoader();
      } catch (SecurityException ignored) {
        // AccessControlException on Google App Engine   
      }
    }
    
    /*
     * Get a resource as a URL using the current class path
     *
     * @param resource - the resource to locate
     * @return the resource or null
     */
    public URL getResourceAsURL(String resource) {
      return getResourceAsURL(resource, getClassLoaders(null));
    }
  
    /*
     * Get a resource from the classpath, starting with a specific class loader
     *
     * @param resource    - the resource to find
     * @param classLoader - the first classloader to try
     * @return the stream or null
     */
    public URL getResourceAsURL(String resource, ClassLoader classLoader) {
      return getResourceAsURL(resource, getClassLoaders(classLoader));
    }
  
    /*
     * Get a resource from the classpath
     *
     * @param resource - the resource to find
     * @return the stream or null
     */
    public InputStream getResourceAsStream(String resource) {
      return getResourceAsStream(resource, getClassLoaders(null));
    }
  
    /*
     * Get a resource from the classpath, starting with a specific class loader
     *
     * @param resource    - the resource to find
     * @param classLoader - the first class loader to try
     * @return the stream or null
     */
    public InputStream getResourceAsStream(String resource, ClassLoader classLoader) {
      return getResourceAsStream(resource, getClassLoaders(classLoader));
    }
  
    /*
     * Find a class on the classpath (or die trying)
     *
     * @param name - the class to look for
     * @return - the class
     * @throws ClassNotFoundException Duh.
     */
    public Class<?> classForName(String name) throws ClassNotFoundException {
      return classForName(name, getClassLoaders(null));
    }
  
    /*
     * Find a class on the classpath, starting with a specific classloader (or die trying)
     *
     * @param name        - the class to look for
     * @param classLoader - the first classloader to try
     * @return - the class
     * @throws ClassNotFoundException Duh.
     */
   public Class<?> classForName(String name, ClassLoader classLoader) throws ClassNotFoundException {
     return classForName(name, getClassLoaders(classLoader));
   }
 
   /*
    * Try to get a resource from a group of classloaders
    *
    * @param resource    - the resource to get
    * @param classLoader - the classloaders to examine
    * @return the resource or null
    */
   InputStream getResourceAsStream(String resource, ClassLoader[] classLoader) {
     for (ClassLoader cl : classLoader) {
       if (null != cl) {
 
         // try to find the resource as passed
         InputStream returnValue = cl.getResourceAsStream(resource);
 
         // now, some class loaders want this leading "/", so we'll add it and try again if we didn't find the resource
         if (null == returnValue) {
           returnValue = cl.getResourceAsStream("/" + resource);
         }
 
         if (null != returnValue) {
           return returnValue;
         }
       }
     }
     return null;
   }
 
   /*
    * Get a resource as a URL using the current class path
    *
    * @param resource    - the resource to locate
    * @param classLoader - the class loaders to examine
    * @return the resource or null
    */
   URL getResourceAsURL(String resource, ClassLoader[] classLoader) {
 
     URL url;
 
     for (ClassLoader cl : classLoader) {
 
       if (null != cl) {
 
         // look for the resource as passed in...
         url = cl.getResource(resource);
 
         // ...but some class loaders want this leading "/", so we'll add it
         // and try again if we didn't find the resource
         if (null == url) {
           url = cl.getResource("/" + resource);
         }
 
         // "It's always in the last place I look for it!"
         // ... because only an idiot would keep looking for it after finding it, so stop looking already.
         if (null != url) {
           return url;
         }
 
       }
 
     }
 
     // didn't find it anywhere.
     return null;
 
   }
 
   /*
    * Attempt to load a class from a group of classloaders
    *
    * @param name        - the class to load
    * @param classLoader - the group of classloaders to examine
    * @return the class
    * @throws ClassNotFoundException - Remember the wisdom of Judge Smails: Well, the world needs ditch diggers, too.
    */
   Class<?> classForName(String name, ClassLoader[] classLoader) throws ClassNotFoundException {
 
     for (ClassLoader cl : classLoader) {
 
       if (null != cl) {
 
         try {
 
           Class<?> c = Class.forName(name, true, cl);
 
           if (null != c) {
             return c;
           }
 
         } catch (ClassNotFoundException e) {
           // we'll ignore this until all classloaders fail to locate the class
         }
 
       }
 
     }
 
     throw new ClassNotFoundException("Cannot find class: " + name);
 
   }
 
   ClassLoader[] getClassLoaders(ClassLoader classLoader) {
     return new ClassLoader[]{
         classLoader,
         defaultClassLoader,
         Thread.currentThread().getContextClassLoader(),
         getClass().getClassLoader(),
         systemClassLoader};
   }
 
 }