Source Code Cross Referenced for CachedIntrospectionResults.java in  » J2EE » spring-framework-2.0.6 » org » springframework » beans » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » J2EE » spring framework 2.0.6 » org.springframework.beans 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * Copyright 2002-2007 the original author or authors.
003:         *
004:         * Licensed under the Apache License, Version 2.0 (the "License");
005:         * you may not use this file except in compliance with the License.
006:         * You may obtain a copy of the License at
007:         *
008:         *      http://www.apache.org/licenses/LICENSE-2.0
009:         *
010:         * Unless required by applicable law or agreed to in writing, software
011:         * distributed under the License is distributed on an "AS IS" BASIS,
012:         * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013:         * See the License for the specific language governing permissions and
014:         * limitations under the License.
015:         */
016:
017:        package org.springframework.beans;
018:
019:        import java.beans.BeanInfo;
020:        import java.beans.IntrospectionException;
021:        import java.beans.Introspector;
022:        import java.beans.PropertyDescriptor;
023:        import java.lang.ref.Reference;
024:        import java.lang.ref.WeakReference;
025:        import java.util.Collections;
026:        import java.util.HashMap;
027:        import java.util.HashSet;
028:        import java.util.Iterator;
029:        import java.util.Map;
030:        import java.util.Set;
031:        import java.util.WeakHashMap;
032:
033:        import org.apache.commons.logging.Log;
034:        import org.apache.commons.logging.LogFactory;
035:
036:        /**
037:         * Internal class that caches JavaBeans {@link java.beans.PropertyDescriptor}
038:         * information for a Java class. Not intended for direct use by application code.
039:         *
040:         * <p>Necessary as {@link java.beans.Introspector#getBeanInfo()} in JDK 1.3 will
041:         * return a new deep copy of the BeanInfo every time we ask for it. We take the
042:         * opportunity to cache property descriptors by method name for fast lookup.
043:         * Furthermore, we do our own caching of descriptors here, rather than rely on
044:         * the JDK's system-wide BeanInfo cache (to avoid leaks on ClassLoader shutdown).
045:         *
046:         * <p>Information is cached statically, so we don't need to create new
047:         * objects of this class for every JavaBean we manipulate. Hence, this class
048:         * implements the factory design pattern, using a private constructor and
049:         * a static {@link #forClass(Class)} factory method to obtain instances.
050:         *
051:         * @author Rod Johnson
052:         * @author Juergen Hoeller
053:         * @since 05 May 2001
054:         * @see #acceptClassLoader(ClassLoader)
055:         * @see #clearClassLoader(ClassLoader)
056:         * @see #forClass(Class)
057:         */
058:        public class CachedIntrospectionResults {
059:
060:            private static final Log logger = LogFactory
061:                    .getLog(CachedIntrospectionResults.class);
062:
063:            /**
064:             * Set of ClassLoaders that this CachedIntrospectionResults class will always
065:             * accept classes from, even if the classes do not qualify as cache-safe.
066:             */
067:            static final Set acceptedClassLoaders = Collections
068:                    .synchronizedSet(new HashSet());
069:
070:            /**
071:             * Map keyed by class containing CachedIntrospectionResults.
072:             * Needs to be a WeakHashMap with WeakReferences as values to allow
073:             * for proper garbage collection in case of multiple class loaders.
074:             */
075:            static final Map classCache = Collections
076:                    .synchronizedMap(new WeakHashMap());
077:
078:            /**
079:             * Accept the given ClassLoader as cache-safe, even if its classes would
080:             * not qualify as cache-safe in this CachedIntrospectionResults class.
081:             * <p>This configuration method is only relevant in scenarios where the Spring
082:             * classes reside in a 'common' ClassLoader (e.g. the system ClassLoader)
083:             * whose lifecycle is not coupled to the application. In such a scenario,
084:             * CachedIntrospectionResults would by default not cache any of the application's
085:             * classes, since they would create a leak in the common ClassLoader.
086:             * <p>Any <code>acceptClassLoader</code> call at application startup should
087:             * be paired with a {@link #clearClassLoader} call at application shutdown.
088:             * @param classLoader the ClassLoader to accept
089:             */
090:            public static void acceptClassLoader(ClassLoader classLoader) {
091:                if (classLoader != null) {
092:                    acceptedClassLoaders.add(classLoader);
093:                }
094:            }
095:
096:            /**
097:             * Clear the introspection cache for the given ClassLoader, removing the
098:             * introspection results for all classes underneath that ClassLoader,
099:             * and deregistering the ClassLoader (and any of its children) from the
100:             * acceptance list.
101:             * @param classLoader the ClassLoader to clear the cache for
102:             */
103:            public static void clearClassLoader(ClassLoader classLoader) {
104:                if (classLoader == null) {
105:                    return;
106:                }
107:                synchronized (classCache) {
108:                    for (Iterator it = classCache.keySet().iterator(); it
109:                            .hasNext();) {
110:                        Class beanClass = (Class) it.next();
111:                        if (isUnderneathClassLoader(beanClass.getClassLoader(),
112:                                classLoader)) {
113:                            it.remove();
114:                        }
115:                    }
116:                }
117:                synchronized (acceptedClassLoaders) {
118:                    for (Iterator it = acceptedClassLoaders.iterator(); it
119:                            .hasNext();) {
120:                        ClassLoader registeredLoader = (ClassLoader) it.next();
121:                        if (isUnderneathClassLoader(registeredLoader,
122:                                classLoader)) {
123:                            it.remove();
124:                        }
125:                    }
126:                }
127:            }
128:
129:            /**
130:             * Create CachedIntrospectionResults for the given bean class.
131:             * <P>We don't want to use synchronization here. Object references are atomic,
132:             * so we can live with doing the occasional unnecessary lookup at startup only.
133:             * @param beanClass the bean class to analyze
134:             * @return the corresponding CachedIntrospectionResults
135:             * @throws BeansException in case of introspection failure
136:             */
137:            static CachedIntrospectionResults forClass(Class beanClass)
138:                    throws BeansException {
139:                CachedIntrospectionResults results = null;
140:                Object value = classCache.get(beanClass);
141:                if (value instanceof  Reference) {
142:                    Reference ref = (Reference) value;
143:                    results = (CachedIntrospectionResults) ref.get();
144:                } else {
145:                    results = (CachedIntrospectionResults) value;
146:                }
147:                if (results == null) {
148:                    // can throw BeansException
149:                    results = new CachedIntrospectionResults(beanClass);
150:                    if (isCacheSafe(beanClass)
151:                            || isClassLoaderAccepted(beanClass.getClassLoader())) {
152:                        classCache.put(beanClass, results);
153:                    } else {
154:                        if (logger.isDebugEnabled()) {
155:                            logger.debug("Not strongly caching class ["
156:                                    + beanClass.getName()
157:                                    + "] because it is not cache-safe");
158:                        }
159:                        classCache.put(beanClass, new WeakReference(results));
160:                    }
161:                }
162:                return results;
163:            }
164:
165:            /**
166:             * Check whether this CachedIntrospectionResults class is configured
167:             * to accept the given ClassLoader.
168:             * @param classLoader the ClassLoader to check
169:             * @return whether the given ClassLoader is accepted
170:             * @see #acceptClassLoader
171:             */
172:            private static boolean isClassLoaderAccepted(ClassLoader classLoader) {
173:                // Iterate over array copy in order to avoid synchronization for the entire
174:                // ClassLoader check (avoiding a synchronized acceptedClassLoaders Iterator).
175:                Object[] acceptedLoaderArray = acceptedClassLoaders.toArray();
176:                for (int i = 0; i < acceptedLoaderArray.length; i++) {
177:                    ClassLoader registeredLoader = (ClassLoader) acceptedLoaderArray[i];
178:                    if (isUnderneathClassLoader(classLoader, registeredLoader)) {
179:                        return true;
180:                    }
181:                }
182:                return false;
183:            }
184:
185:            /**
186:             * Check whether the given class is cache-safe,
187:             * i.e. whether it is loaded by the same class loader as the
188:             * CachedIntrospectionResults class or a parent of it.
189:             * <p>Many thanks to Guillaume Poirier for pointing out the
190:             * garbage collection issues and for suggesting this solution.
191:             * @param clazz the class to analyze
192:             */
193:            private static boolean isCacheSafe(Class clazz) {
194:                ClassLoader target = clazz.getClassLoader();
195:                if (target == null) {
196:                    return false;
197:                }
198:                ClassLoader cur = CachedIntrospectionResults.class
199:                        .getClassLoader();
200:                if (cur == target) {
201:                    return true;
202:                }
203:                while (cur != null) {
204:                    cur = cur.getParent();
205:                    if (cur == target) {
206:                        return true;
207:                    }
208:                }
209:                return false;
210:            }
211:
212:            /**
213:             * Check whether the given ClassLoader is underneath the given parent,
214:             * that is, whether the parent is within the candidate's hierarchy.
215:             * @param candidate the candidate ClassLoader to check
216:             * @param parent the parent ClassLoader to check for
217:             */
218:            private static boolean isUnderneathClassLoader(
219:                    ClassLoader candidate, ClassLoader parent) {
220:                if (candidate == null) {
221:                    return false;
222:                }
223:                if (candidate == parent) {
224:                    return true;
225:                }
226:                ClassLoader classLoaderToCheck = candidate;
227:                while (classLoaderToCheck != null) {
228:                    classLoaderToCheck = classLoaderToCheck.getParent();
229:                    if (classLoaderToCheck == parent) {
230:                        return true;
231:                    }
232:                }
233:                return false;
234:            }
235:
236:            /** The BeanInfo object for the introspected bean class */
237:            private final BeanInfo beanInfo;
238:
239:            /** PropertyDescriptor objects keyed by property name String */
240:            private final Map propertyDescriptorCache;
241:
242:            /**
243:             * Create a new CachedIntrospectionResults instance for the given class.
244:             * @param beanClass the bean class to analyze
245:             * @throws BeansException in case of introspection failure
246:             */
247:            private CachedIntrospectionResults(Class beanClass)
248:                    throws BeansException {
249:                try {
250:                    if (logger.isTraceEnabled()) {
251:                        logger.trace("Getting BeanInfo for class ["
252:                                + beanClass.getName() + "]");
253:                    }
254:                    this .beanInfo = Introspector.getBeanInfo(beanClass);
255:
256:                    // Immediately remove class from Introspector cache, to allow for proper
257:                    // garbage collection on class loader shutdown - we cache it here anyway,
258:                    // in a GC-friendly manner. In contrast to CachedIntrospectionResults,
259:                    // Introspector does not use WeakReferences as values of its WeakHashMap!
260:                    Class classToFlush = beanClass;
261:                    do {
262:                        Introspector.flushFromCaches(classToFlush);
263:                        classToFlush = classToFlush.getSuperclass();
264:                    } while (classToFlush != null);
265:
266:                    if (logger.isTraceEnabled()) {
267:                        logger.trace("Caching PropertyDescriptors for class ["
268:                                + beanClass.getName() + "]");
269:                    }
270:                    this .propertyDescriptorCache = new HashMap();
271:
272:                    // This call is slow so we do it once.
273:                    PropertyDescriptor[] pds = this .beanInfo
274:                            .getPropertyDescriptors();
275:                    for (int i = 0; i < pds.length; i++) {
276:                        PropertyDescriptor pd = pds[i];
277:                        if (logger.isTraceEnabled()) {
278:                            logger
279:                                    .trace("Found bean property '"
280:                                            + pd.getName()
281:                                            + "'"
282:                                            + (pd.getPropertyType() != null ? " of type ["
283:                                                    + pd.getPropertyType()
284:                                                            .getName() + "]"
285:                                                    : "")
286:                                            + (pd.getPropertyEditorClass() != null ? "; editor ["
287:                                                    + pd
288:                                                            .getPropertyEditorClass()
289:                                                            .getName() + "]"
290:                                                    : ""));
291:                        }
292:                        this .propertyDescriptorCache.put(pd.getName(), pd);
293:                    }
294:                } catch (IntrospectionException ex) {
295:                    throw new FatalBeanException(
296:                            "Cannot get BeanInfo for object of class ["
297:                                    + beanClass.getName() + "]", ex);
298:                }
299:            }
300:
301:            BeanInfo getBeanInfo() {
302:                return this .beanInfo;
303:            }
304:
305:            Class getBeanClass() {
306:                return this .beanInfo.getBeanDescriptor().getBeanClass();
307:            }
308:
309:            PropertyDescriptor getPropertyDescriptor(String propertyName) {
310:                return (PropertyDescriptor) this.propertyDescriptorCache
311:                        .get(propertyName);
312:            }
313:
314:        }
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