/*
* Copyright 2002-2007 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
*
* 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.springframework.beans;
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;
/**
* 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 (isCacheSafe(beanClass) || 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 class is cache-safe,
* i.e. whether it is loaded by the same class loader as the
* CachedIntrospectionResults class or a parent of it.
* <p>Many thanks to Guillaume Poirier for pointing out the
* garbage collection issues and for suggesting this solution.
* @param clazz the class to analyze
*/
private static boolean isCacheSafe(Class clazz) {
ClassLoader target = clazz.getClassLoader();
if (target == null) {
return false;
}
ClassLoader cur = CachedIntrospectionResults.class.getClassLoader();
if (cur == target) {
return true;
}
while (cur != null) {
cur = cur.getParent();
if (cur == target) {
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() + "]" : ""));
}
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);
}
}