package us.daveread.basicquery;

 import java.io.File;

 import java.io.IOException;

 import java.net.MalformedURLException;

 import java.net.URL;

 import java.net.URLClassLoader;

 import java.util.ArrayList;

 import java.util.HashMap;

 import java.util.List;

 import java.util.Map;

 import org.apache.log4j.Logger;

 /**

  * <p>

  * Title: Dynamic class loader

  * </p>

  * <p>

  * Description: Dynamically load classes

  * </p>

  * <p>

  * Copyright: Copyright (c) 2004-2014, David Read

  * </p>

  * <p>

  * This program 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.

  * </p>

  * <p>

  * This program 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.

  * </p>

  * <p>

  * You should have received a copy of the GNU General Public License along with

  * this program; if not, write to the Free Software Foundation, Inc., 59 Temple

  * Place, Suite 330, Boston, MA 02111-1307 USA

  * </p>

  * <p>

  * </p>

  * 

  * @author David Read

  */

 public class DynamicClassLoader extends ClassLoader {

   /**

    * Logger

    */

   private static final Logger LOGGER = Logger

       .getLogger(DynamicClassLoader.class);

   /**

    * Cache of loaded classes

    */

   private Map<String, Class<?>> cachedClasses;

   /**

    * URL class loader instance

    */

   private URLClassLoader classLoader;

   /**

    * Create a DynamicClassLoader instance from a list of file paths

    * 

    * @param archives

    *          A list of file paths

    */

   public DynamicClassLoader(List<File> archives) {

     cachedClasses = new HashMap<String, Class<?>>();

     setupClassLoader(archives);

   }

   /**

    * Add the files to the class loader

    * 

    * @param archives

    *          The list of file paths to class libraries

    */

   public void setupClassLoader(List<File> archives) {

     List<URL> urls;

     String fileName;

     urls = new ArrayList<URL>();

     for (int a = 0; a < archives.size(); ++a) {

       try {

         fileName = (archives.get(a)).getCanonicalPath();

         if (fileName.indexOf(":") > 0) {

           fileName = fileName.substring(fileName.indexOf(":") + 1);

         }

         fileName = fileName.replace('\\', '/');

         LOGGER.info("Add to classpath " + fileName);

         urls.add(new URL("jar:file:" + fileName + "!/"));

       } catch (MalformedURLException mal) {

         LOGGER.error("Error with archive URL", mal);

       } catch (IOException io) {

         LOGGER.error("Failure loading archive", io);

       }

       classLoader = new URLClassLoader(urls.toArray(new URL[0]));

     }

   }

   @Override

   public synchronized Class<?> loadClass(String className) throws

       ClassNotFoundException {

     return loadClass(className, false);

   }

   @Override

   public synchronized Class<?> loadClass(String className, boolean resolveIt)

       throws

       ClassNotFoundException {

     Class<?> loadedClass;

     LOGGER.info("Load class [" + className + "]");

     loadedClass = cachedClasses.get(className);

     if (loadedClass == null) {

       try {

         loadedClass = super.findSystemClass(className);

       } catch (ClassNotFoundException exc) {

         // Ignore, try and load it below

         if (LOGGER.isDebugEnabled()) {

           LOGGER.debug(

               "Class not found on system classpath, look in local files", exc);

         }

       }

     }

     if (loadedClass == null) {

       loadedClass = classLoader.loadClass(className);

     }

     if (loadedClass == null) {

       throw new ClassNotFoundException(className);

     }

     if (resolveIt) {

       resolveClass(loadedClass);

     }

     cachedClasses.put(className, loadedClass);

     return loadedClass;

   }

 }