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The ActiveMQ Message Broker and Client implementations
/**
* 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.util.Properties;
import java.util.concurrent.ConcurrentHashMap;
import org.apache.activemq.transport.LogWriter;
import org.apache.activemq.transport.TransportLoggerView;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* 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
* @version $Revision: 612661 $
*/
public class LogWriterFinder {
private static final Log log = LogFactory.getLog(TransportLoggerView.class);
private final String path;
private final ConcurrentHashMap 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);
}
return (LogWriter)clazz.newInstance();
}
/**
* 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) {
}
}
}
}