Java tutorial
/** * Copyright (c) 1997-2013, www.tinygroup.org (luo_guo@icloud.com). * * Licensed under the GPL, Version 3.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.gnu.org/licenses/gpl.html * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.tinygroup.beanwrapper; import java.beans.BeanInfo; import java.beans.IntrospectionException; import java.beans.Introspector; import java.beans.PropertyDescriptor; import java.lang.ref.Reference; import java.lang.ref.WeakReference; import java.util.Collections; import java.util.HashMap; import java.util.HashSet; import java.util.Iterator; import java.util.Map; import java.util.Set; import java.util.WeakHashMap; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.beans.BeansException; import org.springframework.beans.FatalBeanException; import org.springframework.core.JdkVersion; import org.springframework.util.ClassUtils; /** * Internal class that caches JavaBeans {@link java.beans.PropertyDescriptor} * information for a Java class. Not intended for direct use by application code. * * <p>Necessary for own caching of descriptors within the application's * ClassLoader, rather than rely on the JDK's system-wide BeanInfo cache * (in order to avoid leaks on ClassLoader shutdown). * * <p>Information is cached statically, so we don't need to create new * objects of this class for every JavaBean we manipulate. Hence, this class * implements the factory design pattern, using a private constructor and * a static {@link #forClass(Class)} factory method to obtain instances. * * @author Rod Johnson * @author Juergen Hoeller * @since 05 May 2001 * @see #acceptClassLoader(ClassLoader) * @see #clearClassLoader(ClassLoader) * @see #forClass(Class) */ public class CachedIntrospectionResults { private static final Log logger = LogFactory.getLog(CachedIntrospectionResults.class); /** * Set of ClassLoaders that this CachedIntrospectionResults class will always * accept classes from, even if the classes do not qualify as cache-safe. */ static final Set acceptedClassLoaders = Collections.synchronizedSet(new HashSet()); /** * Map keyed by class containing CachedIntrospectionResults. * Needs to be a WeakHashMap with WeakReferences as values to allow * for proper garbage collection in case of multiple class loaders. */ static final Map classCache = Collections.synchronizedMap(new WeakHashMap()); /** * Accept the given ClassLoader as cache-safe, even if its classes would * not qualify as cache-safe in this CachedIntrospectionResults class. * <p>This configuration method is only relevant in scenarios where the Spring * classes reside in a 'common' ClassLoader (e.g. the system ClassLoader) * whose lifecycle is not coupled to the application. In such a scenario, * CachedIntrospectionResults would by default not cache any of the application's * classes, since they would create a leak in the common ClassLoader. * <p>Any <code>acceptClassLoader</code> call at application startup should * be paired with a {@link #clearClassLoader} call at application shutdown. * @param classLoader the ClassLoader to accept */ public static void acceptClassLoader(ClassLoader classLoader) { if (classLoader != null) { acceptedClassLoaders.add(classLoader); } } /** * Clear the introspection cache for the given ClassLoader, removing the * introspection results for all classes underneath that ClassLoader, * and deregistering the ClassLoader (and any of its children) from the * acceptance list. * @param classLoader the ClassLoader to clear the cache for */ public static void clearClassLoader(ClassLoader classLoader) { if (classLoader == null) { return; } synchronized (classCache) { for (Iterator it = classCache.keySet().iterator(); it.hasNext();) { Class beanClass = (Class) it.next(); if (isUnderneathClassLoader(beanClass.getClassLoader(), classLoader)) { it.remove(); } } } synchronized (acceptedClassLoaders) { for (Iterator it = acceptedClassLoaders.iterator(); it.hasNext();) { ClassLoader registeredLoader = (ClassLoader) it.next(); if (isUnderneathClassLoader(registeredLoader, classLoader)) { it.remove(); } } } } /** * Create CachedIntrospectionResults for the given bean class. * <P>We don't want to use synchronization here. Object references are atomic, * so we can live with doing the occasional unnecessary lookup at startup only. * @param beanClass the bean class to analyze * @return the corresponding CachedIntrospectionResults * @throws BeansException in case of introspection failure */ static CachedIntrospectionResults forClass(Class beanClass) throws BeansException { CachedIntrospectionResults results = null; Object value = classCache.get(beanClass); if (value instanceof Reference) { Reference ref = (Reference) value; results = (CachedIntrospectionResults) ref.get(); } else { results = (CachedIntrospectionResults) value; } if (results == null) { // can throw BeansException results = new CachedIntrospectionResults(beanClass); if (ClassUtils.isCacheSafe(beanClass, CachedIntrospectionResults.class.getClassLoader()) || isClassLoaderAccepted(beanClass.getClassLoader())) { classCache.put(beanClass, results); } else { if (logger.isDebugEnabled()) { logger.debug("Not strongly caching class [" + beanClass.getName() + "] because it is not cache-safe"); } classCache.put(beanClass, new WeakReference(results)); } } return results; } /** * Check whether this CachedIntrospectionResults class is configured * to accept the given ClassLoader. * @param classLoader the ClassLoader to check * @return whether the given ClassLoader is accepted * @see #acceptClassLoader */ private static boolean isClassLoaderAccepted(ClassLoader classLoader) { // Iterate over array copy in order to avoid synchronization for the entire // ClassLoader check (avoiding a synchronized acceptedClassLoaders Iterator). Object[] acceptedLoaderArray = acceptedClassLoaders.toArray(); for (int i = 0; i < acceptedLoaderArray.length; i++) { ClassLoader registeredLoader = (ClassLoader) acceptedLoaderArray[i]; if (isUnderneathClassLoader(classLoader, registeredLoader)) { return true; } } return false; } /** * Check whether the given ClassLoader is underneath the given parent, * that is, whether the parent is within the candidate's hierarchy. * @param candidate the candidate ClassLoader to check * @param parent the parent ClassLoader to check for */ private static boolean isUnderneathClassLoader(ClassLoader candidate, ClassLoader parent) { if (candidate == null) { return false; } if (candidate == parent) { return true; } ClassLoader classLoaderToCheck = candidate; while (classLoaderToCheck != null) { classLoaderToCheck = classLoaderToCheck.getParent(); if (classLoaderToCheck == parent) { return true; } } return false; } /** The BeanInfo object for the introspected bean class */ private final BeanInfo beanInfo; /** PropertyDescriptor objects keyed by property name String */ private final Map propertyDescriptorCache; /** * Create a new CachedIntrospectionResults instance for the given class. * @param beanClass the bean class to analyze * @throws BeansException in case of introspection failure */ private CachedIntrospectionResults(Class beanClass) throws BeansException { try { if (logger.isTraceEnabled()) { logger.trace("Getting BeanInfo for class [" + beanClass.getName() + "]"); } this.beanInfo = Introspector.getBeanInfo(beanClass); // Immediately remove class from Introspector cache, to allow for proper // garbage collection on class loader shutdown - we cache it here anyway, // in a GC-friendly manner. In contrast to CachedIntrospectionResults, // Introspector does not use WeakReferences as values of its WeakHashMap! Class classToFlush = beanClass; do { Introspector.flushFromCaches(classToFlush); classToFlush = classToFlush.getSuperclass(); } while (classToFlush != null); if (logger.isTraceEnabled()) { logger.trace("Caching PropertyDescriptors for class [" + beanClass.getName() + "]"); } this.propertyDescriptorCache = new HashMap(); // This call is slow so we do it once. PropertyDescriptor[] pds = this.beanInfo.getPropertyDescriptors(); for (int i = 0; i < pds.length; i++) { PropertyDescriptor pd = pds[i]; if (logger.isTraceEnabled()) { logger.trace("Found bean property '" + pd.getName() + "'" + (pd.getPropertyType() != null ? " of type [" + pd.getPropertyType().getName() + "]" : "") + (pd.getPropertyEditorClass() != null ? "; editor [" + pd.getPropertyEditorClass().getName() + "]" : "")); } if (JdkVersion.isAtLeastJava15()) { pd = new GenericTypeAwarePropertyDescriptor(beanClass, pd.getName(), pd.getReadMethod(), pd.getWriteMethod(), pd.getPropertyEditorClass()); } this.propertyDescriptorCache.put(pd.getName(), pd); } } catch (IntrospectionException ex) { throw new FatalBeanException("Cannot get BeanInfo for object of class [" + beanClass.getName() + "]", ex); } } BeanInfo getBeanInfo() { return this.beanInfo; } Class getBeanClass() { return this.beanInfo.getBeanDescriptor().getBeanClass(); } PropertyDescriptor getPropertyDescriptor(String propertyName) { return (PropertyDescriptor) this.propertyDescriptorCache.get(propertyName); } }