content: /**
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You 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.activemq.util;
  
  import java.io.BufferedInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.lang.reflect.InvocationTargetException;
  import java.util.Properties;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  
  /**
   *
   */
  public class FactoryFinder {
  
      /**
       * The strategy that the FactoryFinder uses to find load and instantiate Objects
       * can be changed out by calling the
       * {@link org.apache.activemq.util.FactoryFinder#setObjectFactory(org.apache.activemq.util.FactoryFinder.ObjectFactory)}
       * method with a custom implementation of ObjectFactory.
       *
       * The default ObjectFactory is typically changed out when running in a specialized container
       * environment where service discovery needs to be done via the container system.  For example,
       * in an OSGi scenario.
       */
      public interface ObjectFactory {
          /**
           * @param path the full service path
           * @return
           */
          public Object create(String path) throws IllegalAccessException, InstantiationException, IOException, ClassNotFoundException;
  
      }
  
      /**
       * The default implementation of Object factory which works well in standalone applications.
       */
      protected static class StandaloneObjectFactory implements ObjectFactory {
          final ConcurrentMap<String, Class> classMap = new ConcurrentHashMap<String, Class>();
  
          @Override
          public Object create(final String path) throws InstantiationException, IllegalAccessException, ClassNotFoundException, IOException {
              Class clazz = classMap.get(path);
              if (clazz == null) {
                  clazz = loadClass(loadProperties(path));
                  classMap.put(path, clazz);
              }
              
              try {
                 return clazz.getConstructor().newInstance();
              } catch (NoSuchMethodException | InvocationTargetException e) {
                 throw new InstantiationException(e.getMessage());
              }
          }
  
          static public Class loadClass(Properties properties) throws ClassNotFoundException, IOException {
  
              String className = properties.getProperty("class");
              if (className == null) {
                  throw new IOException("Expected property is missing: class");
              }
              Class clazz = null;
              ClassLoader loader = Thread.currentThread().getContextClassLoader();
              if (loader != null) {
                  try {
                      clazz = loader.loadClass(className);
                  } catch (ClassNotFoundException e) {
                      // ignore
                  }
              }
              if (clazz == null) {
                  clazz = FactoryFinder.class.getClassLoader().loadClass(className);
              }
  
              return clazz;
          }
  
          static public Properties loadProperties(String uri) throws IOException {
              // lets try the thread context class loader first
              ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
              if (classLoader == null) {
                  classLoader = StandaloneObjectFactory.class.getClassLoader();
              }
              InputStream in = classLoader.getResourceAsStream(uri);
              if (in == null) {
                  in = FactoryFinder.class.getClassLoader().getResourceAsStream(uri);
                  if (in == null) {
                      throw new IOException("Could not find factory class for resource: " + uri);
                  }
              }
  
              // lets load the file
              BufferedInputStream reader = null;
              try {
                  reader = new BufferedInputStream(in);
                  Properties properties = new Properties();
                  properties.load(reader);
                  return properties;
              } finally {
                  try {
                      reader.close();
                  } catch (Exception e) {
                  }
              }
          }
      }
  
      // ================================================================
      // Class methods and properties
      // ================================================================
      private static ObjectFactory objectFactory = new StandaloneObjectFactory();
  
      public static ObjectFactory getObjectFactory() {
          return objectFactory;
      }
  
      public static void setObjectFactory(ObjectFactory objectFactory) {
          FactoryFinder.objectFactory = objectFactory;
      }
  
      // ================================================================
      // Instance methods and properties
      // ================================================================
      private final String path;
  
      public FactoryFinder(String path) {
          this.path = path;
      }
  
      /**
       * Creates a new instance of the given key
       *
       * @param key is the key to add to the path to find a text file containing
       *                the factory name
       * @return a newly created instance
       */
      public Object newInstance(String key) throws IllegalAccessException, InstantiationException, IOException, ClassNotFoundException {
          return objectFactory.create(path+key);
      }
  
  
  }
  