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.logging.log4j.LogManager;
28 import org.apache.logging.log4j.Logger;
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 initialization 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 $Id$
58 */
59 public abstract class BaseInitableBroker
60 implements InitableBroker
61 {
62 /** A repository of Initable instances. */
63 protected Hashtable<String, Initable> initables = new Hashtable<>();
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<>();
71
72 /** Logging */
73 private final Logger log = LogManager.getLogger(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 * @throws 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 {} was requested", className, e);
159 }
160 }
161
162 /**
163 * Provides an instance of Initable class ready to work.
164 *
165 * If the requested class couldn't be instantiated or initialized,
166 * an InstantiationException will be thrown. You needn't handle
167 * this exception in your code, since it indicates fatal
168 * misconfiguration of the system.
169 *
170 * @param className The name of the Initable requested.
171 * @return An instance of the requested Initable.
172 * @throws InstantiationException if there was a problem
173 * during instantiation or initialization of the Initable.
174 */
175 @Override
176 public Initable getInitable(String className)
177 throws InstantiationException
178 {
179 Initable initable;
180 try
181 {
182 initable = getInitableInstance(className);
183 if (!initable.getInit())
184 {
185 synchronized (initable.getClass())
186 {
187 if (!initable.getInit())
188 {
189 initable.init();
190 }
191 if (!initable.getInit())
192 {
193 // this exception will be caught & rethrown by this
194 // very method. getInit() returning false indicates
195 // some initialization issue, which in turn prevents
196 // the InitableBroker from passing a working
197 // instance of the initable to the client.
198 throw new InitializationException(
199 "init() failed to initialize class "
200 + className);
201 }
202 }
203 }
204 return initable;
205 }
206 catch (InitializationException e)
207 {
208 throw new InstantiationException("Class " + className +
209 " failed to initialize", e);
210 }
211 }
212
213 /**
214 * Retrieves an instance of an Initable from the repository.
215 *
216 * If the requested class is not present in the repository, it is
217 * instantiated and passed a reference to the broker, saved and
218 * then returned.
219 *
220 * @param className The name of the class to be instantiated.
221 *
222 * @return an instance of the requested class
223 *
224 * @throws InstantiationException if the requested class can't
225 * be instantiated.
226 */
227 protected Initable getInitableInstance(String className)
228 throws InstantiationException
229 {
230 Initable initable = initables.get(className);
231
232 if (initable == null)
233 {
234 try
235 {
236 initable = (Initable) Class.forName(className).newInstance();
237 }
238
239 // those two errors must be passed to the VM
240 catch (ThreadDeath t)
241 {
242 throw t;
243 }
244 catch (OutOfMemoryError t)
245 {
246 throw t;
247 }
248
249 catch (Throwable t)
250 {
251 // Used to indicate error condition.
252 String msg = null;
253
254 if (t instanceof NoClassDefFoundError)
255 {
256 msg = "A class referenced by " + className +
257 " is unavailable. Check your jars and classes.";
258 }
259 else if (t instanceof ClassNotFoundException)
260 {
261 msg = "Class " + className +
262 " is unavailable. Check your jars and classes.";
263 }
264 else if (t instanceof ClassCastException)
265 {
266 msg = "Class " + className +
267 " doesn't implement Initable.";
268 }
269 else
270 {
271 msg = "Failed to instantiate " + className;
272 }
273
274 throw new InstantiationException(msg, t);
275 }
276
277 initable.setInitableBroker(this);
278 initables.put(className, initable);
279 }
280
281 return initable;
282 }
283
284 }