001 /** 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 package org.apache.activemq.util; 018 019 import java.io.BufferedInputStream; 020 import java.io.IOException; 021 import java.io.InputStream; 022 import java.util.Properties; 023 import java.util.concurrent.ConcurrentHashMap; 024 025 import org.apache.activemq.transport.LogWriter; 026 import org.apache.activemq.transport.TransportLoggerView; 027 import org.apache.commons.logging.Log; 028 import org.apache.commons.logging.LogFactory; 029 030 /** 031 * Class used to find a LogWriter implementation, and returning 032 * a LogWriter object, taking as argument the name of a log writer. 033 * The mapping between the log writer names and the classes 034 * implementing LogWriter is specified by the files in the 035 * resources/META-INF/services/org/apache/activemq/transport/logwriters 036 * directory. 037 * 038 * @author David Martin Clavo david(dot)martin(dot)clavo(at)gmail.com 039 * @version $Revision: 612661 $ 040 */ 041 public class LogWriterFinder { 042 043 private static final Log log = LogFactory.getLog(TransportLoggerView.class); 044 045 private final String path; 046 private final ConcurrentHashMap classMap = new ConcurrentHashMap(); 047 048 /** 049 * Builds a LogWriterFinder that will look for the mappings between 050 * LogWriter names and classes in the directory "path". 051 * @param path The directory where the files that map log writer names to 052 * LogWriter classes are. 053 */ 054 public LogWriterFinder(String path) { 055 this.path = path; 056 } 057 058 /** 059 * Returns a LogWriter object, given a log writer name (for example "default", or "custom"). 060 * Uses a ConcurrentHashMap to cache the Class objects that have already been loaded. 061 * @param logWriterName a log writer name (for example "default", or "custom"). 062 * @return a LogWriter object to be used by the TransportLogger class. 063 * @throws IllegalAccessException 064 * @throws InstantiationException 065 * @throws IOException 066 * @throws ClassNotFoundException 067 */ 068 public LogWriter newInstance(String logWriterName) 069 throws IllegalAccessException, InstantiationException, IOException, ClassNotFoundException 070 { 071 Class clazz = (Class) classMap.get(logWriterName); 072 if (clazz == null) { 073 clazz = newInstance(doFindLogWriterProperties(logWriterName)); 074 classMap.put(logWriterName, clazz); 075 } 076 return (LogWriter)clazz.newInstance(); 077 } 078 079 /** 080 * Loads and returns a class given a Properties object with a "class" property. 081 * @param properties a Properties object with a "class" property. 082 * @return a Class object. 083 * @throws ClassNotFoundException 084 * @throws IOException 085 */ 086 private Class newInstance(Properties properties) throws ClassNotFoundException, IOException { 087 088 String className = properties.getProperty("class"); 089 if (className == null) { 090 throw new IOException("Expected property is missing: " + "class"); 091 } 092 Class clazz; 093 try { 094 clazz = Thread.currentThread().getContextClassLoader().loadClass(className); 095 } catch (ClassNotFoundException e) { 096 clazz = LogWriterFinder.class.getClassLoader().loadClass(className); 097 } 098 099 return clazz; 100 } 101 102 /** 103 * Given a log writer name, returns a Properties object with a "class" property 104 * whose value is a String with the name of the class to be loaded. 105 * @param logWriterName a log writer name. 106 * @return a Properties object with a "class" property 107 * @throws IOException 108 */ 109 protected Properties doFindLogWriterProperties (String logWriterName) throws IOException { 110 111 String uri = path + logWriterName; 112 113 // lets try the thread context class loader first 114 ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); 115 if (classLoader == null) classLoader = getClass().getClassLoader(); 116 InputStream in = classLoader.getResourceAsStream(uri); 117 if (in == null) { 118 in = LogWriterFinder.class.getClassLoader().getResourceAsStream(uri); 119 if (in == null) { 120 log.error("Could not find log writer for resource: " + uri); 121 throw new IOException("Could not find log writer for resource: " + uri); 122 } 123 } 124 125 // lets load the file 126 BufferedInputStream reader = null; 127 Properties properties = new Properties(); 128 try { 129 reader = new BufferedInputStream(in); 130 properties.load(reader); 131 return properties; 132 } finally { 133 try { 134 reader.close(); 135 } catch (Exception e) { 136 } 137 } 138 } 139 140 141 }