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;
  
  import org.apache.activemq.transport.LogWriter;
  import org.apache.activemq.transport.TransportLoggerView;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Class used to find a LogWriter implementation, and returning
   * a LogWriter object, taking as argument the name of a log writer.
   * The mapping between the log writer names and the classes
   * implementing LogWriter is specified by the files in the
   * resources/META-INF/services/org/apache/activemq/transport/logwriters
   * directory.
   *
   * @author David Martin Clavo david(dot)martin(dot)clavo(at)gmail.com
   *
   */
  public class LogWriterFinder {
  
      private static final Logger log = LoggerFactory.getLogger(TransportLoggerView.class);
  
      private final String path;
      private final ConcurrentMap classMap = new ConcurrentHashMap();
  
      /**
       * Builds a LogWriterFinder that will look for the mappings between
       * LogWriter names and classes in the directory "path".
       * @param path The directory where the files that map log writer names to
       * LogWriter classes are.
       */
      public LogWriterFinder(String path) {
          this.path = path;
      }
  
      /**
       * Returns a LogWriter object, given a log writer name (for example "default", or "custom").
       * Uses a ConcurrentHashMap to cache the Class objects that have already been loaded.
       * @param logWriterName a log writer name (for example "default", or "custom").
       * @return a LogWriter object to be used by the TransportLogger class.
       * @throws IllegalAccessException
       * @throws InstantiationException
       * @throws IOException
       * @throws ClassNotFoundException
       */
      public LogWriter newInstance(String logWriterName)
      throws IllegalAccessException, InstantiationException, IOException, ClassNotFoundException
      {
          Class clazz = (Class) classMap.get(logWriterName);
          if (clazz == null) {
              clazz = newInstance(doFindLogWriterProperties(logWriterName));
              classMap.put(logWriterName, clazz);
          }
          try {
              return LogWriter.class.cast(clazz.getConstructor().newInstance());
          } catch (InvocationTargetException | NoSuchMethodException e) {
          	throw new InstantiationException(e.getMessage());
          }
      }
  
      /**
       * Loads and returns a class given a Properties object with a "class" property.
       * @param properties a Properties object with a "class" property.
       * @return a Class object.
       * @throws ClassNotFoundException
       * @throws IOException
       */
      private Class newInstance(Properties properties) throws ClassNotFoundException, IOException {
  
          String className = properties.getProperty("class");
          if (className == null) {
              throw new IOException("Expected property is missing: " + "class");
          }
          Class clazz;
          try {
              clazz = Thread.currentThread().getContextClassLoader().loadClass(className);
          } catch (ClassNotFoundException e) {
              clazz = LogWriterFinder.class.getClassLoader().loadClass(className);
          }
  
          return clazz;
      }
  
      /**
       * Given a log writer name, returns a Properties object with a "class" property
       * whose value is a String with the name of the class to be loaded.
       * @param logWriterName a log writer name.
       * @return a Properties object with a "class" property
       * @throws IOException
       */
      protected Properties doFindLogWriterProperties (String logWriterName) throws IOException {
  
          String uri = path + logWriterName;
  
          // lets try the thread context class loader first
          ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
          if (classLoader == null) classLoader = getClass().getClassLoader();
          InputStream in = classLoader.getResourceAsStream(uri);
          if (in == null) {
              in = LogWriterFinder.class.getClassLoader().getResourceAsStream(uri);
              if (in == null) {
                  log.error("Could not find log writer for resource: " + uri);
                  throw new IOException("Could not find log writer for resource: " + uri);
              }
          }
  
          // lets load the file
          BufferedInputStream reader = null;
          Properties properties = new Properties();
          try {
              reader = new BufferedInputStream(in);
              properties.load(reader);
              return properties;
          } finally {
              try {
                  reader.close();
              } catch (Exception e) {
              }
          }
      }
  
  
  }
  