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 1078552 2011-03-06 19:58:46Z 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 public void initClass(String className, Object data) 96 throws InitializationException 97 { 98 // make sure that only one thread calls this method recursively 99 synchronized (stack) 100 { 101 int pos = stack.search(className); 102 if (pos != -1) 103 { 104 StringBuffer msg = new StringBuffer().append(className) 105 .append(" couldn't be initialized because of circular depency chain:\n"); 106 for (int i = pos; i > 0; i--) 107 { 108 msg.append(stack.elementAt(stack.size() - i - 1) + "->"); 109 } 110 msg.append(className).append('\n'); 111 112 throw new InitializationException(msg.toString()); 113 } 114 try 115 { 116 stack.push(className); 117 Initable instance = getInitableInstance(className); 118 if (!instance.getInit()) 119 { 120 // this call might result in an indirect recursion 121 instance.init(data); 122 } 123 } 124 finally 125 { 126 // Succeeded or not, make sure the name gets off the stack. 127 stack.pop(); 128 } 129 } 130 } 131 132 /** 133 * Shuts down an <code>Initable</code>. 134 * 135 * This method is used to release resources allocated by an 136 * <code>Initable</code>, and return it to its initial (uninitailized) 137 * state. 138 * 139 * @param className The name of the class to be uninitialized. 140 */ 141 public void shutdownClass(String className) 142 { 143 try 144 { 145 Initable initable = getInitableInstance(className); 146 if (initable.getInit()) 147 { 148 initable.shutdown(); 149 ((BaseInitable) initable).setInit(false); 150 } 151 } 152 catch (InstantiationException e) 153 { 154 // Shutdown of a nonexistent class was requested. 155 // This does not hurt anything, so we log the error and continue. 156 log.error("Shutdown of a nonexistent class " + 157 className + " was requested", e); 158 } 159 } 160 161 /** 162 * Provides an instance of Initable class ready to work. 163 * 164 * If the requested class couldn't be instatiated or initialized, 165 * an InstantiationException will be thrown. You needn't handle 166 * this exception in your code, since it indicates fatal 167 * misconfigurtion of the system. 168 * 169 * @param className The name of the Initable requested. 170 * @return An instance of the requested Initable. 171 * @exception InstantiationException if there was a problem 172 * during instantiation or initialization of the Initable. 173 */ 174 public Initable getInitable(String className) 175 throws InstantiationException 176 { 177 Initable initable; 178 try 179 { 180 initable = getInitableInstance(className); 181 if (!initable.getInit()) 182 { 183 synchronized (initable.getClass()) 184 { 185 if (!initable.getInit()) 186 { 187 initable.init(); 188 } 189 if (!initable.getInit()) 190 { 191 // this exception will be caught & rethrown by this 192 // very method. getInit() returning false indicates 193 // some initialization issue, which in turn prevents 194 // the InitableBroker from passing a working 195 // instance of the initable to the client. 196 throw new InitializationException( 197 "init() failed to initialize class " 198 + className); 199 } 200 } 201 } 202 return initable; 203 } 204 catch (InitializationException e) 205 { 206 throw new InstantiationException("Class " + className + 207 " failed to initialize", e); 208 } 209 } 210 211 /** 212 * Retrieves an instance of an Initable from the repository. 213 * 214 * If the requested class is not present in the repository, it is 215 * instantiated and passed a reference to the broker, saved and 216 * then returned. 217 * 218 * @param className The name of the class to be instantiated. 219 * @exception InstantiationException if the requested class can't 220 * be instantiated. 221 */ 222 protected Initable getInitableInstance(String className) 223 throws InstantiationException 224 { 225 Initable initable = initables.get(className); 226 227 if (initable == null) 228 { 229 try 230 { 231 initable = (Initable) Class.forName(className).newInstance(); 232 } 233 234 // those two errors must be passed to the VM 235 catch (ThreadDeath t) 236 { 237 throw t; 238 } 239 catch (OutOfMemoryError t) 240 { 241 throw t; 242 } 243 244 catch (Throwable t) 245 { 246 // Used to indicate error condition. 247 String msg = null; 248 249 if (t instanceof NoClassDefFoundError) 250 { 251 msg = "A class referenced by " + className + 252 " is unavailable. Check your jars and classes."; 253 } 254 else if (t instanceof ClassNotFoundException) 255 { 256 msg = "Class " + className + 257 " is unavailable. Check your jars and classes."; 258 } 259 else if (t instanceof ClassCastException) 260 { 261 msg = "Class " + className + 262 " doesn't implement Initable."; 263 } 264 else 265 { 266 msg = "Failed to instantiate " + className; 267 } 268 269 throw new InstantiationException(msg, t); 270 } 271 272 initable.setInitableBroker(this); 273 initables.put(className, initable); 274 } 275 276 return initable; 277 } 278 279 }