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; 025 026/** 027 * 028 */ 029public class FactoryFinder { 030 031 /** 032 * The strategy that the FactoryFinder uses to find load and instantiate Objects 033 * can be changed out by calling the 034 * {@link org.apache.activemq.util.FactoryFinder#setObjectFactory(org.apache.activemq.util.FactoryFinder.ObjectFactory)} 035 * method with a custom implementation of ObjectFactory. 036 * 037 * The default ObjectFactory is typically changed out when running in a specialized container 038 * environment where service discovery needs to be done via the container system. For example, 039 * in an OSGi scenario. 040 */ 041 public interface ObjectFactory { 042 /** 043 * @param path the full service path 044 * @return 045 */ 046 public Object create(String path) throws IllegalAccessException, InstantiationException, IOException, ClassNotFoundException; 047 048 } 049 050 /** 051 * The default implementation of Object factory which works well in standalone applications. 052 */ 053 protected static class StandaloneObjectFactory implements ObjectFactory { 054 final ConcurrentMap<String, Class> classMap = new ConcurrentHashMap<String, Class>(); 055 056 @Override 057 public Object create(final String path) throws InstantiationException, IllegalAccessException, ClassNotFoundException, IOException { 058 Class clazz = classMap.get(path); 059 if (clazz == null) { 060 clazz = loadClass(loadProperties(path)); 061 classMap.put(path, clazz); 062 } 063 return clazz.newInstance(); 064 } 065 066 static public Class loadClass(Properties properties) throws ClassNotFoundException, IOException { 067 068 String className = properties.getProperty("class"); 069 if (className == null) { 070 throw new IOException("Expected property is missing: class"); 071 } 072 Class clazz = null; 073 ClassLoader loader = Thread.currentThread().getContextClassLoader(); 074 if (loader != null) { 075 try { 076 clazz = loader.loadClass(className); 077 } catch (ClassNotFoundException e) { 078 // ignore 079 } 080 } 081 if (clazz == null) { 082 clazz = FactoryFinder.class.getClassLoader().loadClass(className); 083 } 084 085 return clazz; 086 } 087 088 static public Properties loadProperties(String uri) throws IOException { 089 // lets try the thread context class loader first 090 ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); 091 if (classLoader == null) { 092 classLoader = StandaloneObjectFactory.class.getClassLoader(); 093 } 094 InputStream in = classLoader.getResourceAsStream(uri); 095 if (in == null) { 096 in = FactoryFinder.class.getClassLoader().getResourceAsStream(uri); 097 if (in == null) { 098 throw new IOException("Could not find factory class for resource: " + uri); 099 } 100 } 101 102 // lets load the file 103 BufferedInputStream reader = null; 104 try { 105 reader = new BufferedInputStream(in); 106 Properties properties = new Properties(); 107 properties.load(reader); 108 return properties; 109 } finally { 110 try { 111 reader.close(); 112 } catch (Exception e) { 113 } 114 } 115 } 116 } 117 118 // ================================================================ 119 // Class methods and properties 120 // ================================================================ 121 private static ObjectFactory objectFactory = new StandaloneObjectFactory(); 122 123 public static ObjectFactory getObjectFactory() { 124 return objectFactory; 125 } 126 127 public static void setObjectFactory(ObjectFactory objectFactory) { 128 FactoryFinder.objectFactory = objectFactory; 129 } 130 131 // ================================================================ 132 // Instance methods and properties 133 // ================================================================ 134 private final String path; 135 136 public FactoryFinder(String path) { 137 this.path = path; 138 } 139 140 /** 141 * Creates a new instance of the given key 142 * 143 * @param key is the key to add to the path to find a text file containing 144 * the factory name 145 * @return a newly created instance 146 */ 147 public Object newInstance(String key) throws IllegalAccessException, InstantiationException, IOException, ClassNotFoundException { 148 return objectFactory.create(path+key); 149 } 150 151 152}