001package org.apache.turbine.services;
002
003
004/*
005 * Licensed to the Apache Software Foundation (ASF) under one
006 * or more contributor license agreements.  See the NOTICE file
007 * distributed with this work for additional information
008 * regarding copyright ownership.  The ASF licenses this file
009 * to you under the Apache License, Version 2.0 (the
010 * "License"); you may not use this file except in compliance
011 * with the License.  You may obtain a copy of the License at
012 *
013 *   http://www.apache.org/licenses/LICENSE-2.0
014 *
015 * Unless required by applicable law or agreed to in writing,
016 * software distributed under the License is distributed on an
017 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
018 * KIND, either express or implied.  See the License for the
019 * specific language governing permissions and limitations
020 * under the License.
021 */
022
023
024import java.util.Hashtable;
025import java.util.Stack;
026
027import org.apache.commons.logging.Log;
028import org.apache.commons.logging.LogFactory;
029
030/**
031 * A generic implementation of <code>InitableBroker</code>.
032 * Functionality provided by the broker includes:
033 *
034 * <ul>
035 *
036 * <li>Maintaining single instance of each <code>Initable</code> in
037 * the system.</li>
038 *
039 * <li>Early initialization of <code>Initables</code> during system
040 * startup.</li>
041 *
042 * <li>Late initialization of <code>Initables</code> before they are
043 * used.</li>
044 *
045 * <li>Providing instances of <code>Initables</code> to requesting
046 * parties.</li>
047 *
048 * <li>Maintaining dependencies between <code>Initables</code> during
049 * early initialization phases, including circular dependencies
050 * detection.</li>
051 *
052 * </ul>
053 *
054 * @author <a href="mailto:burton@apache.org">Kevin Burton</a>
055 * @author <a href="mailto:krzewski@e-point.pl">Rafal Krzewski</a>
056 * @author <a href="mailto:hps@intermeta.de">Henning P. Schmiedehausen</a>
057 * @version $Id: BaseInitableBroker.java 1773378 2016-12-09 13:19:59Z tv $
058 */
059public abstract class BaseInitableBroker
060        implements InitableBroker
061{
062    /** A repository of Initable instances. */
063    protected Hashtable<String, Initable> initables = new Hashtable<String, Initable>();
064
065    /**
066     * Names of classes being early-initialized are pushed onto this
067     * stack.  A name appearing twice indicates a circular dependency
068     * chain.
069     */
070    protected Stack<String> stack = new Stack<String>();
071
072    /** Logging */
073    private final Log log = LogFactory.getLog(this.getClass());
074
075    /**
076     * Default constructor of InitableBroker.
077     *
078     * This constructor does nothing. Your brokers should be
079     * singletons, therefore their constructors should be
080     * private. They should also have public YourBroker getInstance()
081     * methods.
082     */
083    protected BaseInitableBroker()
084    {
085        // empty
086    }
087
088    /**
089     * Performs early initialization of an Initable class.
090     *
091     * @param className The name of the class to be initialized.
092     * @param data An Object to be used for initialization activities.
093     * @throws InitializationException Initialization was not successful.
094     */
095    @Override
096    public void initClass(String className, Object data)
097            throws InitializationException
098    {
099        // 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     * @throws 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     *
223     * @return an instance of the requested class
224     *
225     * @throws InstantiationException if the requested class can't
226     * be instantiated.
227     */
228    protected Initable getInitableInstance(String className)
229            throws InstantiationException
230    {
231        Initable initable = initables.get(className);
232
233        if (initable == null)
234        {
235            try
236            {
237                initable = (Initable) Class.forName(className).newInstance();
238            }
239
240                    // those two errors must be passed to the VM
241            catch (ThreadDeath t)
242            {
243                throw t;
244            }
245            catch (OutOfMemoryError t)
246            {
247                throw t;
248            }
249
250            catch (Throwable t)
251            {
252                // Used to indicate error condition.
253                String msg = null;
254
255                if (t instanceof NoClassDefFoundError)
256                {
257                    msg = "A class referenced by " + className +
258                            " is unavailable. Check your jars and classes.";
259                }
260                else if (t instanceof ClassNotFoundException)
261                {
262                    msg = "Class " + className +
263                            " is unavailable. Check your jars and classes.";
264                }
265                else if (t instanceof ClassCastException)
266                {
267                    msg = "Class " + className +
268                            " doesn't implement Initable.";
269                }
270                else
271                {
272                    msg = "Failed to instantiate " + className;
273                }
274
275                throw new InstantiationException(msg, t);
276            }
277
278            initable.setInitableBroker(this);
279            initables.put(className, initable);
280        }
281
282        return initable;
283    }
284
285}