SpringIOC核心源码学习（二）：容器初始化过程

转至：http://www.iteye.com/topic/1115391

ClassPathXmlApplicationContext 这个容器的实现作为基础，学习容器的初始化过程。

ClassPathXmlApplicationContext 类体系结构

?public void refresh() throws BeansException, IllegalStateException {synchronized (this.startupShutdownMonitor) {// Prepare this context for refreshing.prepareRefresh();// Tell the subclass to refresh the internal bean factory.ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();// Prepare the bean factory for use in this context.prepareBeanFactory(beanFactory);try {// Allows post-processing of the bean factory in context subclasses.postProcessBeanFactory(beanFactory);// Invoke factory processors registered as beans in the context.invokeBeanFactoryPostProcessors(beanFactory);// Register bean processors that intercept bean creation.registerBeanPostProcessors(beanFactory);// Initialize message source for this context.initMessageSource();// Initialize event multicaster for this context.initApplicationEventMulticaster();// Initialize other special beans in specific context subclasses.onRefresh();// Check for listener beans and register them.registerListeners();// Instantiate all remaining (non-lazy-init) singletons.finishBeanFactoryInitialization(beanFactory);// Last step: publish corresponding event.finishRefresh();}catch (BeansException ex) {// Destroy already created singletons to avoid dangling resources.beanFactory.destroySingletons();// Reset 'active' flag.cancelRefresh(ex);// Propagate exception to caller.throw ex;}}}

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解释如下：

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?public void preInstantiateSingletons() throws BeansException {if (this.logger.isInfoEnabled()) {this.logger.info("Pre-instantiating singletons in " + this);}synchronized (this.beanDefinitionMap) {for (Iterator it = this.beanDefinitionNames.iterator(); it.hasNext();) {String beanName = (String) it.next();RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {//对非抽象、单例的和非延迟加载的对象进行实例化。if (isFactoryBean(beanName)) {FactoryBean factory = (FactoryBean) getBean(FACTORY_BEAN_PREFIX + beanName);if (factory instanceof SmartFactoryBean && ((SmartFactoryBean) factory).isEagerInit()) {getBean(beanName);}}else {getBean(beanName);}}}}}

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?<?xml version="1.0" encoding="GB2312"?><!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN" "http://www.springframework.org/dtd/spring-beans-2.0.dtd"><beans default-autowire="byName"><bean id="otherBean" scope="prototype"/><bean id="myBean" lazy-init="true"/><bean id="singletonBean" src="/img/2012/06/25/110320591.gif">?protected Object doGetBean(final String name, final Class requiredType, final Object[] args, boolean typeCheckOnly) throws BeansException {final String beanName = transformedBeanName(name);Object bean = null;// Eagerly check singleton cache for manually registered singletons.Object sharedInstance = getSingleton(beanName);if (sharedInstance != null && args == null) {if (logger.isDebugEnabled()) {if (isSingletonCurrentlyInCreation(beanName)) {logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +"' that is not fully initialized yet - a consequence of a circular reference");}else {logger.debug("Returning cached instance of singleton bean '" + beanName + "'");}}bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);}else {// Fail if we're already creating this bean instance:// We're assumably within a circular reference.if (isPrototypeCurrentlyInCreation(beanName)) {throw new BeanCurrentlyInCreationException(beanName);}// Check if bean definition exists in this factory.BeanFactory parentBeanFactory = getParentBeanFactory();if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {// Not found -> check parent.String nameToLookup = originalBeanName(name);if (args != null) {// Delegation to parent with explicit args.return parentBeanFactory.getBean(nameToLookup, args);}else {// No args -> delegate to standard getBean method.return parentBeanFactory.getBean(nameToLookup, requiredType);}}if (!typeCheckOnly) {markBeanAsCreated(beanName);}final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);checkMergedBeanDefinition(mbd, beanName, args);// Guarantee initialization of beans that the current bean depends on.String[] dependsOn = mbd.getDependsOn();if (dependsOn != null) {for (int i = 0; i < dependsOn.length; i++) {String dependsOnBean = dependsOn[i];getBean(dependsOnBean);registerDependentBean(dependsOnBean, beanName);}}// Create bean instance.if (mbd.isSingleton()) {//单例对象创建过程,间接通过getSingleton方法来创建，里面会实现将单例对象缓存sharedInstance = getSingleton(beanName, new ObjectFactory() {public Object getObject() throws BeansException {try {return createBean(beanName, mbd, args);}catch (BeansException ex) {// Explicitly remove instance from singleton cache: It might have been put there// eagerly by the creation process, to allow for circular reference resolution.// Also remove any beans that received a temporary reference to the bean.destroySingleton(beanName);throw ex;}}});bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);}else if (mbd.isPrototype()) {//非单例对象创建// It's a prototype -> create a new instance.Object prototypeInstance = null;try {beforePrototypeCreation(beanName);prototypeInstance = createBean(beanName, mbd, args);//直接调用createBean}finally {afterPrototypeCreation(beanName);}bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);}else {String scopeName = mbd.getScope();final Scope scope = (Scope) this.scopes.get(scopeName);if (scope == null) {throw new IllegalStateException("No Scope registered for scope '" + scopeName + "'");}try {Object scopedInstance = scope.get(beanName, new ObjectFactory() {public Object getObject() throws BeansException {beforePrototypeCreation(beanName);try {return createBean(beanName, mbd, args);}finally {afterPrototypeCreation(beanName);}}});bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);}catch (IllegalStateException ex) {throw new BeanCreationException(beanName,"Scope '" + scopeName + "' is not active for the current thread; " +"consider defining a scoped proxy for this bean if you intend to refer to it from a singleton",ex);}}}// Check if required type matches the type of the actual bean instance.if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());}return bean;}

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?protected Object createBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)throws BeanCreationException {AccessControlContext acc = AccessController.getContext();return AccessController.doPrivileged(new PrivilegedAction() {public Object run() {if (logger.isDebugEnabled()) {logger.debug("Creating instance of bean '" + beanName + "'");}// Make sure bean class is actually resolved at this point.resolveBeanClass(mbd, beanName);// Prepare method overrides.try {mbd.prepareMethodOverrides();}catch (BeanDefinitionValidationException ex) {throw new BeanDefinitionStoreException(mbd.getResourceDescription(),beanName, "Validation of method overrides failed", ex);}try {// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.Object bean = resolveBeforeInstantiation(beanName, mbd);if (bean != null) {return bean;}}catch (Throwable ex) {throw new BeanCreationException(mbd.getResourceDescription(), beanName,"BeanPostProcessor before instantiation of bean failed", ex);}Object beanInstance = doCreateBean(beanName, mbd, args);if (logger.isDebugEnabled()) {logger.debug("Finished creating instance of bean '" + beanName + "'");}return beanInstance;}}, acc);}

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createBean 会调用 doCreateBean 方法：

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?protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {// Instantiate the bean.BeanWrapper instanceWrapper = null;if (mbd.isSingleton()) {instanceWrapper = (BeanWrapper) this.factoryBeanInstanceCache.remove(beanName);}if (instanceWrapper == null) {instanceWrapper = createBeanInstance(beanName, mbd, args);}final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);Class beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);// Allow post-processors to modify the merged bean definition.synchronized (mbd.postProcessingLock) {if (!mbd.postProcessed) {applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);mbd.postProcessed = true;}}// Eagerly cache singletons to be able to resolve circular references// even when triggered by lifecycle interfaces like BeanFactoryAware.boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&isSingletonCurrentlyInCreation(beanName));if (earlySingletonExposure) {if (logger.isDebugEnabled()) {logger.debug("Eagerly caching bean '" + beanName +"' to allow for resolving potential circular references");}addSingletonFactory(beanName, new ObjectFactory() {public Object getObject() throws BeansException {return getEarlyBeanReference(beanName, mbd, bean);}});}// Initialize the bean instance.Object exposedObject = bean;try {populateBean(beanName, mbd, instanceWrapper);exposedObject = initializeBean(beanName, exposedObject, mbd);}catch (Throwable ex) {if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {throw (BeanCreationException) ex;}else {throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);}}if (earlySingletonExposure) {Object earlySingletonReference = getSingleton(beanName, false);if (earlySingletonReference != null) {if (exposedObject == bean) {exposedObject = earlySingletonReference;}else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {String[] dependentBeans = getDependentBeans(beanName);Set actualDependentBeans = new LinkedHashSet(dependentBeans.length);for (int i = 0; i < dependentBeans.length; i++) {String dependentBean = dependentBeans[i];if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {actualDependentBeans.add(dependentBean);}}if (!actualDependentBeans.isEmpty()) {throw new BeanCurrentlyInCreationException(beanName,"Bean with name '" + beanName + "' has been injected into other beans [" +StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +"] in its raw version as part of a circular reference, but has eventually been " +"wrapped. This means that said other beans do not use the final version of the " +"bean. This is often the result of over-eager type matching - consider using " +"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");}}}}// Register bean as disposable.registerDisposableBeanIfNecessary(beanName, bean, mbd);return exposedObject;}

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?if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {MutablePropertyValues newPvs = new MutablePropertyValues(pvs);// Add property values based on autowire by name if applicable.if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {autowireByName(beanName, mbd, bw, newPvs);}//根据名字注入// Add property values based on autowire by type if applicable.if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {autowireByType(beanName, mbd, bw, newPvs);}//根据类型注入pvs = newPvs;}

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?protected Object initializeBean(String beanName, Object bean, RootBeanDefinition mbd) {if (bean instanceof BeanNameAware) {((BeanNameAware) bean).setBeanName(beanName);}if (bean instanceof BeanClassLoaderAware) {((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());}if (bean instanceof BeanFactoryAware) {((BeanFactoryAware) bean).setBeanFactory(this);}Object wrappedBean = bean;if (mbd == null || !mbd.isSynthetic()) {wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);}try {invokeInitMethods(beanName, wrappedBean, mbd);}catch (Throwable ex) {throw new BeanCreationException((mbd != null ? mbd.getResourceDescription() : null),beanName, "Invocation of init method failed", ex);}if (mbd == null || !mbd.isSynthetic()) {wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);}return wrappedBean;}

?其中invokeInitMethods实现如下：

?protected void invokeInitMethods(String beanName, Object bean, RootBeanDefinition mbd)throws Throwable {boolean isInitializingBean = (bean instanceof InitializingBean);if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {if (logger.isDebugEnabled()) {logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");}((InitializingBean) bean).afterPropertiesSet();//调用afterPropertiesSet方法}String initMethodName = (mbd != null ? mbd.getInitMethodName() : null);if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&!mbd.isExternallyManagedInitMethod(initMethodName)) {invokeCustomInitMethod(beanName, bean, initMethodName, mbd.isEnforceInitMethod());}}

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总结

以上基本描述了 spring 容器的初始化过程和 bean 的创建过程。主要还是从大处着眼，很多细节没有涉及到。代码阅读总体感觉就是 spring 的代码抽象很好，结合结构读起来还是蛮顺利的。后面的学习将从细节着手。

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