content: /*
   * Copyright (C) 2013 Glyptodon LLC
   *
   * 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 org.glyptodon.guacamole.net.basic;
  
  import java.io.File;
  import java.io.FilenameFilter;
  import java.net.MalformedURLException;
  import java.net.URL;
  import java.net.URLClassLoader;
  import java.security.AccessController;
  import java.security.PrivilegedActionException;
  import java.security.PrivilegedExceptionAction;
  import java.util.ArrayList;
  import java.util.Collection;
  import org.glyptodon.guacamole.GuacamoleException;
  import org.glyptodon.guacamole.net.basic.properties.BasicGuacamoleProperties;
  import org.glyptodon.guacamole.properties.GuacamoleProperties;
  
  /**
   * A ClassLoader implementation which finds classes within a configurable
   * directory. This directory is set within guacamole.properties.
   *
   * @author Michael Jumper
   */
  public class GuacamoleClassLoader extends ClassLoader {
  
      /**
       * Class loader which will load classes from the classpath specified
       * in guacamole.properties.
       */
      private URLClassLoader classLoader = null;
  
      /**
       * Any exception that occurs while the class loader is being instantiated.
       */
      private static GuacamoleException exception = null;
  
      /**
       * Singleton instance of the GuacamoleClassLoader.
       */
      private static GuacamoleClassLoader instance = null;
  
      static {
  
          try {
              // Attempt to create singleton classloader which loads classes from
              // all .jar's in the lib directory defined in guacamole.properties
              instance = AccessController.doPrivileged(new PrivilegedExceptionAction<GuacamoleClassLoader>() {
  
                  @Override
                  public GuacamoleClassLoader run() throws GuacamoleException {
                      return new GuacamoleClassLoader(
                          GuacamoleProperties.getProperty(BasicGuacamoleProperties.LIB_DIRECTORY)
                      );
                  }
  
              });
          }
  
          catch (PrivilegedActionException e) {
              // On error, record exception
              exception = (GuacamoleException) e.getException();
          }
  
      }
  
      /**
       * Creates a new GuacamoleClassLoader which reads classes from the given
       * directory.
       *
       * @param libDirectory The directory to load classes from.
       * @throws GuacamoleException If the file given is not a director, or if
       *                            an error occurs while constructing the URL
       *                            for the backing classloader.
       */
      private GuacamoleClassLoader(File libDirectory) throws GuacamoleException {
  
          // If no directory provided, just direct requests to parent classloader
          if (libDirectory == null)
              return;
  
          // Validate directory is indeed a directory
          if (!libDirectory.isDirectory())
              throw new GuacamoleException(libDirectory + " is not a directory.");
  
          // Get list of URLs for all .jar's in the lib directory
          Collection<URL> jarURLs = new ArrayList<URL>();
          for (File file : libDirectory.listFiles(new FilenameFilter() {
  
              @Override
              public boolean accept(File dir, String name) {
  
                  // If it ends with .jar, accept the file
                  return name.endsWith(".jar");
  
              }
  
          })) {
  
              try {
  
                  // Add URL for the .jar to the jar URL list
                  jarURLs.add(file.toURI().toURL());
  
              }
              catch (MalformedURLException e) {
                  throw new GuacamoleException(e);
              }
  
          }
  
          // Set delegate classloader to new URLClassLoader which loads from the
          // .jars found above.
  
          URL[] urls = new URL[jarURLs.size()];
          classLoader = new URLClassLoader(
              jarURLs.toArray(urls),
              getClass().getClassLoader()
          );
  
      }
  
      /**
       * Returns an instance of a GuacamoleClassLoader which finds classes
       * within the directory configured in guacamole.properties.
       *
       * @return An instance of a GuacamoleClassLoader.
       * @throws GuacamoleException If no instance could be returned due to an
       *                            error.
       */
      public static GuacamoleClassLoader getInstance() throws GuacamoleException {
  
          // If instance could not be created, rethrow original exception
          if (exception != null) throw exception;
  
          return instance;
  
      }
  
      @Override
      protected Class<?> findClass(String name) throws ClassNotFoundException {
  
          // If no classloader, use default loader
          if (classLoader == null)
              return Class.forName(name);
  
          // Otherwise, delegate
          return classLoader.loadClass(name);
  
      }
  
  }
  