Java tutorial
/* * Copyright 2002-2006 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.factory.support; import java.util.ArrayList; import java.util.Iterator; import java.util.List; import java.util.Map; import java.util.Set; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.beans.BeanWrapper; import org.springframework.beans.BeansException; import org.springframework.beans.factory.BeanCreationException; import org.springframework.beans.factory.config.BeanDefinition; import org.springframework.beans.factory.config.BeanDefinitionHolder; import org.springframework.beans.factory.config.RuntimeBeanReference; import org.springframework.beans.factory.config.TypedStringValue; import org.springframework.core.CollectionFactory; /** * Helper class for use by BeanFactory implementations, * resolving values contained in BeanDefinition objects * into the actual values applied to th target bean instance. * * <p>Operates on an AbstractBeanFactory and a plain BeanDefinition object. * Used by AbstractAutowireCapableBeanFactory. * * @author Juergen Hoeller * @since 1.2 * @see AbstractAutowireCapableBeanFactory */ public class BeanDefinitionValueResolver { protected static final Log logger = LogFactory.getLog(BeanDefinitionValueResolver.class); private final AbstractBeanFactory beanFactory; private final String beanName; private final BeanDefinition beanDefinition; /** * Create a new BeanDefinitionValueResolver for the given BeanFactory * and BeanDefinition. * @param beanFactory the BeanFactory to resolve against * @param beanName the name of the bean that we work on * @param beanDefinition the BeanDefinition of the bean that we work on */ public BeanDefinitionValueResolver(AbstractBeanFactory beanFactory, String beanName, BeanDefinition beanDefinition) { this.beanFactory = beanFactory; this.beanName = beanName; this.beanDefinition = beanDefinition; } /** * Given a PropertyValue, return a value, resolving any references to other * beans in the factory if necessary. The value could be: * <li>A BeanDefinition, which leads to the creation of a corresponding * new bean instance. Singleton flags and names of such "inner beans" * are always ignored: Inner beans are anonymous prototypes. * <li>A RuntimeBeanReference, which must be resolved. * <li>A ManagedList. This is a special collection that may contain * RuntimeBeanReferences or Collections that will need to be resolved. * <li>A ManagedSet. May also contain RuntimeBeanReferences or * Collections that will need to be resolved. * <li>A ManagedMap. In this case the value may be a RuntimeBeanReference * or Collection that will need to be resolved. * <li>An ordinary object or <code>null</code>, in which case it's left alone. */ public Object resolveValueIfNecessary(String argName, Object value) throws BeansException { // We must check each value to see whether it requires a runtime reference // to another bean to be resolved. if (value instanceof BeanDefinitionHolder) { // Resolve BeanDefinitionHolder: contains BeanDefinition with name and aliases. BeanDefinitionHolder bdHolder = (BeanDefinitionHolder) value; return resolveInnerBeanDefinition(argName, bdHolder.getBeanName(), bdHolder.getBeanDefinition()); } else if (value instanceof BeanDefinition) { // Resolve plain BeanDefinition, without contained name: use dummy name. BeanDefinition bd = (BeanDefinition) value; return resolveInnerBeanDefinition(argName, "(inner bean)", bd); } else if (value instanceof RuntimeBeanReference) { RuntimeBeanReference ref = (RuntimeBeanReference) value; return resolveReference(argName, ref); } else if (value instanceof ManagedList) { // May need to resolve contained runtime references. return resolveManagedList(argName, (List) value); } else if (value instanceof ManagedSet) { // May need to resolve contained runtime references. return resolveManagedSet(argName, (Set) value); } else if (value instanceof ManagedMap) { // May need to resolve contained runtime references. return resolveManagedMap(argName, (Map) value); } else if (value instanceof TypedStringValue) { // Convert value to target type here. TypedStringValue typedStringValue = (TypedStringValue) value; try { return this.beanFactory.doTypeConversionIfNecessary(typedStringValue.getValue(), typedStringValue.getTargetType()); } catch (Throwable ex) { // Improve the message by showing the context. throw new BeanCreationException(this.beanDefinition.getResourceDescription(), this.beanName, "Error converting typed String value for " + argName, ex); } } else { // No need to resolve value... return value; } } /** * Resolve an inner bean definition. */ private Object resolveInnerBeanDefinition(String argName, String innerBeanName, BeanDefinition innerBd) throws BeansException { if (logger.isDebugEnabled()) { logger.debug("Resolving inner bean definition '" + innerBeanName + "' of bean '" + this.beanName + "'"); } try { RootBeanDefinition mergedInnerBd = this.beanFactory.getMergedBeanDefinition(innerBeanName, innerBd); Object innerBean = this.beanFactory.createBean(innerBeanName, mergedInnerBd, null); if (mergedInnerBd.isSingleton()) { this.beanFactory.registerDependentBean(innerBeanName, this.beanName); } return this.beanFactory.getObjectForSharedInstance(innerBeanName, innerBean); } catch (BeansException ex) { throw new BeanCreationException(this.beanDefinition.getResourceDescription(), this.beanName, "Cannot create inner bean '" + innerBeanName + "' while setting " + argName, ex); } } /** * Resolve a reference to another bean in the factory. */ private Object resolveReference(String argName, RuntimeBeanReference ref) throws BeansException { if (logger.isDebugEnabled()) { logger.debug("Resolving reference from property " + argName + " in bean '" + this.beanName + "' to bean '" + ref.getBeanName() + "'"); } try { if (ref.isToParent()) { if (this.beanFactory.getParentBeanFactory() == null) { throw new BeanCreationException(this.beanDefinition.getResourceDescription(), this.beanName, "Can't resolve reference to bean '" + ref.getBeanName() + "' in parent factory: no parent factory available"); } return this.beanFactory.getParentBeanFactory().getBean(ref.getBeanName()); } else { Object bean = this.beanFactory.getBean(ref.getBeanName()); if (this.beanDefinition.isSingleton()) { this.beanFactory.registerDependentBean(ref.getBeanName(), this.beanName); } return bean; } } catch (BeansException ex) { throw new BeanCreationException(this.beanDefinition.getResourceDescription(), this.beanName, "Cannot resolve reference to bean '" + ref.getBeanName() + "' while setting " + argName, ex); } } /** * For each element in the ManagedList, resolve reference if necessary. */ private List resolveManagedList(String argName, List ml) throws BeansException { List resolved = new ArrayList(ml.size()); for (int i = 0; i < ml.size(); i++) { resolved.add(resolveValueIfNecessary( argName + " with key " + BeanWrapper.PROPERTY_KEY_PREFIX + i + BeanWrapper.PROPERTY_KEY_SUFFIX, ml.get(i))); } return resolved; } /** * For each element in the ManagedList, resolve reference if necessary. */ private Set resolveManagedSet(String argName, Set ms) throws BeansException { Set resolved = CollectionFactory.createLinkedSetIfPossible(ms.size()); int i = 0; for (Iterator it = ms.iterator(); it.hasNext();) { resolved.add(resolveValueIfNecessary( argName + " with key " + BeanWrapper.PROPERTY_KEY_PREFIX + i + BeanWrapper.PROPERTY_KEY_SUFFIX, it.next())); i++; } return resolved; } /** * For each element in the ManagedMap, resolve reference if necessary. */ private Map resolveManagedMap(String argName, Map mm) throws BeansException { Map resolved = CollectionFactory.createLinkedMapIfPossible(mm.size()); Iterator it = mm.entrySet().iterator(); while (it.hasNext()) { Map.Entry entry = (Map.Entry) it.next(); Object resolvedKey = resolveValueIfNecessary(argName, entry.getKey()); Object resolvedValue = resolveValueIfNecessary(argName + " with key " + BeanWrapper.PROPERTY_KEY_PREFIX + entry.getKey() + BeanWrapper.PROPERTY_KEY_SUFFIX, entry.getValue()); resolved.put(resolvedKey, resolvedValue); } return resolved; } }