1 package org.apache.turbine.services; 2 3 4 /* 5 * Licensed to the Apache Software Foundation (ASF) under one 6 * or more contributor license agreements. See the NOTICE file 7 * distributed with this work for additional information 8 * regarding copyright ownership. The ASF licenses this file 9 * to you under the Apache License, Version 2.0 (the 10 * "License"); you may not use this file except in compliance 11 * with the License. You may obtain a copy of the License at 12 * 13 * http://www.apache.org/licenses/LICENSE-2.0 14 * 15 * Unless required by applicable law or agreed to in writing, 16 * software distributed under the License is distributed on an 17 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 18 * KIND, either express or implied. See the License for the 19 * specific language governing permissions and limitations 20 * under the License. 21 */ 22 23 24 import java.util.Hashtable; 25 import java.util.Stack; 26 27 import org.apache.commons.logging.Log; 28 import org.apache.commons.logging.LogFactory; 29 30 /** 31 * A generic implementation of <code>InitableBroker</code>. 32 * Functionality provided by the broker includes: 33 * 34 * <ul> 35 * 36 * <li>Maintaining single instance of each <code>Initable</code> in 37 * the system.</li> 38 * 39 * <li>Early initialization of <code>Initables</code> during system 40 * startup.</li> 41 * 42 * <li>Late initialization of <code>Initables</code> before they are 43 * used.</li> 44 * 45 * <li>Providing instances of <code>Initables</code> to requesting 46 * parties.</li> 47 * 48 * <li>Maintaining dependencies between <code>Initables</code> during 49 * early initalization phases, including circular dependencies 50 * detection.</li> 51 * 52 * </ul> 53 * 54 * @author <a href="mailto:burton@apache.org">Kevin Burton</a> 55 * @author <a href="mailto:krzewski@e-point.pl">Rafal Krzewski</a> 56 * @author <a href="mailto:hps@intermeta.de">Henning P. Schmiedehausen</a> 57 * @version $Id: BaseInitableBroker.java 1706239 2015-10-01 13:18:35Z tv $ 58 */ 59 public abstract class BaseInitableBroker 60 implements InitableBroker 61 { 62 /** A repository of Initable instances. */ 63 protected Hashtable<String, Initable> initables = new Hashtable<String, Initable>(); 64 65 /** 66 * Names of classes being early-initialized are pushed onto this 67 * stack. A name appearing twice indicates a circular dependency 68 * chain. 69 */ 70 protected Stack<String> stack = new Stack<String>(); 71 72 /** Logging */ 73 private final Log log = LogFactory.getLog(this.getClass()); 74 75 /** 76 * Default constructor of InitableBroker. 77 * 78 * This constructor does nothing. Your brokers should be 79 * singletons, therefore their constructors should be 80 * private. They should also have public YourBroker getInstance() 81 * methods. 82 */ 83 protected BaseInitableBroker() 84 { 85 // empty 86 } 87 88 /** 89 * Performs early initialization of an Initable class. 90 * 91 * @param className The name of the class to be initialized. 92 * @param data An Object to be used for initialization activities. 93 * @exception InitializationException Initialization was not successful. 94 */ 95 @Override 96 public void initClass(String className, Object data) 97 throws InitializationException 98 { 99 // make sure that only one thread calls this method recursively 100 synchronized (stack) 101 { 102 int pos = stack.search(className); 103 if (pos != -1) 104 { 105 StringBuilder msg = new StringBuilder().append(className) 106 .append(" couldn't be initialized because of circular dependency chain:\n"); 107 for (int i = pos; i > 0; i--) 108 { 109 msg.append(stack.elementAt(stack.size() - i - 1) + "->"); 110 } 111 msg.append(className).append('\n'); 112 113 throw new InitializationException(msg.toString()); 114 } 115 try 116 { 117 stack.push(className); 118 Initable instance = getInitableInstance(className); 119 if (!instance.getInit()) 120 { 121 // this call might result in an indirect recursion 122 instance.init(data); 123 } 124 } 125 finally 126 { 127 // Succeeded or not, make sure the name gets off the stack. 128 stack.pop(); 129 } 130 } 131 } 132 133 /** 134 * Shuts down an <code>Initable</code>. 135 * 136 * This method is used to release resources allocated by an 137 * <code>Initable</code>, and return it to its initial (uninitialized) 138 * state. 139 * 140 * @param className The name of the class to be uninitialized. 141 */ 142 @Override 143 public void shutdownClass(String className) 144 { 145 try 146 { 147 Initable initable = getInitableInstance(className); 148 if (initable.getInit()) 149 { 150 initable.shutdown(); 151 ((BaseInitable) initable).setInit(false); 152 } 153 } 154 catch (InstantiationException e) 155 { 156 // Shutdown of a nonexistent class was requested. 157 // This does not hurt anything, so we log the error and continue. 158 log.error("Shutdown of a nonexistent class " + 159 className + " was requested", e); 160 } 161 } 162 163 /** 164 * Provides an instance of Initable class ready to work. 165 * 166 * If the requested class couldn't be instantiated or initialized, 167 * an InstantiationException will be thrown. You needn't handle 168 * this exception in your code, since it indicates fatal 169 * misconfiguration of the system. 170 * 171 * @param className The name of the Initable requested. 172 * @return An instance of the requested Initable. 173 * @exception InstantiationException if there was a problem 174 * during instantiation or initialization of the Initable. 175 */ 176 @Override 177 public Initable getInitable(String className) 178 throws InstantiationException 179 { 180 Initable initable; 181 try 182 { 183 initable = getInitableInstance(className); 184 if (!initable.getInit()) 185 { 186 synchronized (initable.getClass()) 187 { 188 if (!initable.getInit()) 189 { 190 initable.init(); 191 } 192 if (!initable.getInit()) 193 { 194 // this exception will be caught & rethrown by this 195 // very method. getInit() returning false indicates 196 // some initialization issue, which in turn prevents 197 // the InitableBroker from passing a working 198 // instance of the initable to the client. 199 throw new InitializationException( 200 "init() failed to initialize class " 201 + className); 202 } 203 } 204 } 205 return initable; 206 } 207 catch (InitializationException e) 208 { 209 throw new InstantiationException("Class " + className + 210 " failed to initialize", e); 211 } 212 } 213 214 /** 215 * Retrieves an instance of an Initable from the repository. 216 * 217 * If the requested class is not present in the repository, it is 218 * instantiated and passed a reference to the broker, saved and 219 * then returned. 220 * 221 * @param className The name of the class to be instantiated. 222 * @exception InstantiationException if the requested class can't 223 * be instantiated. 224 */ 225 protected Initable getInitableInstance(String className) 226 throws InstantiationException 227 { 228 Initable initable = initables.get(className); 229 230 if (initable == null) 231 { 232 try 233 { 234 initable = (Initable) Class.forName(className).newInstance(); 235 } 236 237 // those two errors must be passed to the VM 238 catch (ThreadDeath t) 239 { 240 throw t; 241 } 242 catch (OutOfMemoryError t) 243 { 244 throw t; 245 } 246 247 catch (Throwable t) 248 { 249 // Used to indicate error condition. 250 String msg = null; 251 252 if (t instanceof NoClassDefFoundError) 253 { 254 msg = "A class referenced by " + className + 255 " is unavailable. Check your jars and classes."; 256 } 257 else if (t instanceof ClassNotFoundException) 258 { 259 msg = "Class " + className + 260 " is unavailable. Check your jars and classes."; 261 } 262 else if (t instanceof ClassCastException) 263 { 264 msg = "Class " + className + 265 " doesn't implement Initable."; 266 } 267 else 268 { 269 msg = "Failed to instantiate " + className; 270 } 271 272 throw new InstantiationException(msg, t); 273 } 274 275 initable.setInitableBroker(this); 276 initables.put(className, initable); 277 } 278 279 return initable; 280 } 281 282 }