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 */ 017package org.apache.activemq.util; 018 019import java.io.BufferedInputStream; 020import java.io.IOException; 021import java.io.InputStream; 022import java.util.Properties; 023import java.util.concurrent.ConcurrentHashMap; 024import java.util.concurrent.ConcurrentMap; 025 026import org.apache.activemq.transport.LogWriter; 027import org.apache.activemq.transport.TransportLoggerView; 028import org.slf4j.Logger; 029import org.slf4j.LoggerFactory; 030 031/** 032 * Class used to find a LogWriter implementation, and returning 033 * a LogWriter object, taking as argument the name of a log writer. 034 * The mapping between the log writer names and the classes 035 * implementing LogWriter is specified by the files in the 036 * resources/META-INF/services/org/apache/activemq/transport/logwriters 037 * directory. 038 * 039 * @author David Martin Clavo david(dot)martin(dot)clavo(at)gmail.com 040 * 041 */ 042public class LogWriterFinder { 043 044 private static final Logger log = LoggerFactory.getLogger(TransportLoggerView.class); 045 046 private final String path; 047 private final ConcurrentMap classMap = new ConcurrentHashMap(); 048 049 /** 050 * Builds a LogWriterFinder that will look for the mappings between 051 * LogWriter names and classes in the directory "path". 052 * @param path The directory where the files that map log writer names to 053 * LogWriter classes are. 054 */ 055 public LogWriterFinder(String path) { 056 this.path = path; 057 } 058 059 /** 060 * Returns a LogWriter object, given a log writer name (for example "default", or "custom"). 061 * Uses a ConcurrentHashMap to cache the Class objects that have already been loaded. 062 * @param logWriterName a log writer name (for example "default", or "custom"). 063 * @return a LogWriter object to be used by the TransportLogger class. 064 * @throws IllegalAccessException 065 * @throws InstantiationException 066 * @throws IOException 067 * @throws ClassNotFoundException 068 */ 069 public LogWriter newInstance(String logWriterName) 070 throws IllegalAccessException, InstantiationException, IOException, ClassNotFoundException 071 { 072 Class clazz = (Class) classMap.get(logWriterName); 073 if (clazz == null) { 074 clazz = newInstance(doFindLogWriterProperties(logWriterName)); 075 classMap.put(logWriterName, clazz); 076 } 077 return (LogWriter)clazz.newInstance(); 078 } 079 080 /** 081 * Loads and returns a class given a Properties object with a "class" property. 082 * @param properties a Properties object with a "class" property. 083 * @return a Class object. 084 * @throws ClassNotFoundException 085 * @throws IOException 086 */ 087 private Class newInstance(Properties properties) throws ClassNotFoundException, IOException { 088 089 String className = properties.getProperty("class"); 090 if (className == null) { 091 throw new IOException("Expected property is missing: " + "class"); 092 } 093 Class clazz; 094 try { 095 clazz = Thread.currentThread().getContextClassLoader().loadClass(className); 096 } catch (ClassNotFoundException e) { 097 clazz = LogWriterFinder.class.getClassLoader().loadClass(className); 098 } 099 100 return clazz; 101 } 102 103 /** 104 * Given a log writer name, returns a Properties object with a "class" property 105 * whose value is a String with the name of the class to be loaded. 106 * @param logWriterName a log writer name. 107 * @return a Properties object with a "class" property 108 * @throws IOException 109 */ 110 protected Properties doFindLogWriterProperties (String logWriterName) throws IOException { 111 112 String uri = path + logWriterName; 113 114 // lets try the thread context class loader first 115 ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); 116 if (classLoader == null) classLoader = getClass().getClassLoader(); 117 InputStream in = classLoader.getResourceAsStream(uri); 118 if (in == null) { 119 in = LogWriterFinder.class.getClassLoader().getResourceAsStream(uri); 120 if (in == null) { 121 log.error("Could not find log writer for resource: " + uri); 122 throw new IOException("Could not find log writer for resource: " + uri); 123 } 124 } 125 126 // lets load the file 127 BufferedInputStream reader = null; 128 Properties properties = new Properties(); 129 try { 130 reader = new BufferedInputStream(in); 131 properties.load(reader); 132 return properties; 133 } finally { 134 try { 135 reader.close(); 136 } catch (Exception e) { 137 } 138 } 139 } 140 141 142}