001 // Copyright 2004, 2005 The Apache Software Foundation
002 //
003 // Licensed under the Apache License, Version 2.0 (the "License");
004 // you may not use this file except in compliance with the License.
005 // You may obtain a copy of the License at
006 //
007 // http://www.apache.org/licenses/LICENSE-2.0
008 //
009 // Unless required by applicable law or agreed to in writing, software
010 // distributed under the License is distributed on an "AS IS" BASIS,
011 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012 // See the License for the specific language governing permissions and
013 // limitations under the License.
014
015 package org.apache.hivemind.servlet;
016
017 import java.io.IOException;
018 import java.util.Locale;
019
020 import javax.servlet.Filter;
021 import javax.servlet.FilterChain;
022 import javax.servlet.FilterConfig;
023 import javax.servlet.ServletContext;
024 import javax.servlet.ServletException;
025 import javax.servlet.ServletRequest;
026 import javax.servlet.ServletResponse;
027 import javax.servlet.http.HttpServletRequest;
028
029 import org.apache.commons.logging.Log;
030 import org.apache.commons.logging.LogFactory;
031 import org.apache.hivemind.ClassResolver;
032 import org.apache.hivemind.ModuleDescriptorProvider;
033 import org.apache.hivemind.Registry;
034 import org.apache.hivemind.impl.DefaultClassResolver;
035 import org.apache.hivemind.impl.RegistryBuilder;
036 import org.apache.hivemind.impl.XmlModuleDescriptorProvider;
037 import org.apache.hivemind.util.ContextResource;
038
039 /**
040 * Servlet filter that constructs the Registry at startup. It ensures that each request is properly
041 * terminated with a call to
042 * {@link org.apache.hivemind.service.ThreadEventNotifier#fireThreadCleanup()}. It also makes the
043 * Registry available during the request by storing it as a request attribute.
044 *
045 * @author Howard Lewis Ship
046 */
047 public class HiveMindFilter implements Filter
048 {
049 private static final Log LOG = LogFactory.getLog(HiveMindFilter.class);
050
051 /**
052 * Request attribute key that stores the Registry.
053 */
054
055 static final String REQUEST_KEY = "org.apache.hivemind.RequestRegistry";
056
057 static final String REBUILD_REQUEST_KEY = "org.apache.hivemind.RebuildRegistry";
058
059 /** @since 1.1 */
060 static final String HIVE_MODULE_XML = "/WEB-INF/hivemodule.xml";
061
062 private FilterConfig _filterConfig;
063
064 private Registry _registry;
065
066 /**
067 * Constructs a {@link Registry} and stores it into the <code>ServletContext</code>. Any
068 * exception throws is logged.
069 */
070 public void init(FilterConfig config) throws ServletException
071 {
072 _filterConfig = config;
073
074 initializeRegistry();
075
076 }
077
078 private void initializeRegistry()
079 {
080 long startTime = System.currentTimeMillis();
081
082 LOG.info(ServletMessages.filterInit());
083
084 try
085 {
086 _registry = constructRegistry(_filterConfig);
087
088 LOG.info(ServletMessages.constructedRegistry(_registry, System.currentTimeMillis()
089 - startTime));
090 }
091 catch (Exception ex)
092 {
093 LOG.error(ex.getMessage(), ex);
094 }
095 }
096
097 /**
098 * Invoked from {@link #init(FilterConfig)} to actually construct the Registry. Subclasses may
099 * override if they have specific initialization needs, or have nonstandard rules for finding
100 * HiveMind module deployment descriptors.
101 */
102 protected Registry constructRegistry(FilterConfig config)
103 {
104 RegistryBuilder builder = new RegistryBuilder();
105
106 ClassResolver resolver = new DefaultClassResolver();
107
108 builder.addModuleDescriptorProvider(getModuleDescriptorProvider(resolver));
109
110 addWebInfDescriptor(config.getServletContext(), resolver, builder);
111
112 return builder.constructRegistry(getRegistryLocale());
113 }
114
115 /**
116 * Invoked from {@link #constructRegistry(FilterConfig)} to add WEB-INF/hivemodule.xml to
117 * the registry, if it exists.
118 *
119 * @since 1.1
120 */
121
122 protected void addWebInfDescriptor(ServletContext context, ClassResolver resolver,
123 RegistryBuilder builder)
124 {
125 ContextResource r = new ContextResource(context, HIVE_MODULE_XML);
126
127 if (r.getResourceURL() != null)
128 {
129 ModuleDescriptorProvider provider = new XmlModuleDescriptorProvider(resolver, r);
130
131 builder.addModuleDescriptorProvider(provider);
132 }
133 }
134
135 /**
136 * Returns the default Locale. Subclasses may override to select a particular locale for the
137 * Registry.
138 */
139 protected Locale getRegistryLocale()
140 {
141 return Locale.getDefault();
142 }
143
144 /**
145 * Returns the {@link ModuleDescriptorProvider} to be used to construct the Registry. This
146 * implementation returns the default {@link XmlModuleDescriptorProvider}. May be overridden by
147 * subclasses.
148 *
149 * @since 1.1
150 */
151 protected ModuleDescriptorProvider getModuleDescriptorProvider(ClassResolver resolver)
152 {
153 return new XmlModuleDescriptorProvider(resolver);
154 }
155
156 /**
157 * Passes the request to the filter chain, but then invokes {@link Registry#cleanupThread()}
158 * (from a finally block).
159 */
160 public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
161 throws IOException, ServletException
162 {
163 try
164 {
165 // I believe the _registry will only be null in a couple of test situations.
166
167 if (_registry != null)
168 _registry.setupThread();
169
170 request.setAttribute(REQUEST_KEY, _registry);
171
172 chain.doFilter(request, response);
173 }
174 finally
175 {
176 cleanupThread();
177
178 checkRegistryRebuild(request);
179 }
180 }
181
182 private synchronized void checkRegistryRebuild(ServletRequest request)
183 {
184 if (request.getAttribute(REBUILD_REQUEST_KEY) == null)
185 return;
186
187 Registry oldRegistry = _registry;
188
189 // Replace the old Registry with a new one. All other threads, but this
190 // one, will begin using the new Registry. Hopefully, we didn't get
191 // rebuild requests on multiple threads.
192
193 initializeRegistry();
194
195 // Shutdown the old Registry. Perhaps we should sleep for a moment, first,
196 // to help ensure that other threads have "cleared out". If not, we'll see some
197 // instability at the instant we shutdown (i.e., all the proxies will get disabled).
198 // Alternately, we should create a WeakReference based monitor that shuts down the
199 // old registry when it is no longer used by any other threads. For the moment,
200 // this functionality is limited to development-time only (not production), so it isn't
201 // urgent.
202
203 oldRegistry.shutdown();
204 }
205
206 /**
207 * Cleanup the thread, ignoring any exceptions that may be thrown.
208 */
209 private void cleanupThread()
210 {
211 try
212 {
213 _registry.cleanupThread();
214 }
215 catch (Exception ex)
216 {
217 LOG.error(ServletMessages.filterCleanupError(ex), ex);
218 }
219 }
220
221 /**
222 * Invokes {@link Registry#shutdown()}.
223 */
224 public void destroy()
225 {
226 if (_registry != null)
227 _registry.shutdown();
228
229 _filterConfig = null;
230 }
231
232 /**
233 * Returns the {@link Registry} that was stored as a request attribute inside method
234 * {@link #doFilter(ServletRequest, ServletResponse, FilterChain)}.
235 */
236 public static Registry getRegistry(HttpServletRequest request)
237 {
238 return (Registry) request.getAttribute(REQUEST_KEY);
239 }
240
241 /**
242 * Sets a flag in the request that will cause the current Registry to be shutdown and replaced
243 * with a new Registry (at the end of the current request).
244 */
245 public static void rebuildRegistry(HttpServletRequest request)
246 {
247 request.setAttribute(REBUILD_REQUEST_KEY, Boolean.TRUE);
248 }
249
250 }