Spring源码分析之Bean的加载流程

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spring版本为4.3.6.RELEASE

不管是xml方式配置bean还是基于注解的形式，最终都会调用AbstractApplicationContext的refresh方法：

@Override
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) {if (logger.isWarnEnabled()) {logger.warn("Exception encountered during context initialization - " +"cancelling refresh attempt: " + ex);}// Destroy already created singletons to avoid dangling resources.destroyBeans();// Reset 'active' flag.cancelRefresh(ex);// Propagate exception to caller.throw ex;}finally {// Reset common introspection caches in Spring's core, since we// might not ever need metadata for singleton beans anymore...resetCommonCaches();}}
}

1、prepareRefresh();

刷新的准备工作，记录容器启动的时间，并设置容器处于活跃状态。

2、ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

刷新并获取beanFactory

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {refreshBeanFactory();ConfigurableListableBeanFactory beanFactory = getBeanFactory();if (logger.isDebugEnabled()) {logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);}return beanFactory;
}protected abstract void refreshBeanFactory() throws BeansException, IllegalStateException;@Override
public abstract ConfigurableListableBeanFactory getBeanFactory() throws IllegalStateException;

这个refreshBeanFactory(),getBeanFactory()由子类AbstractRefreshableApplicationContext来实现：

@Override
protected final void refreshBeanFactory() throws BeansException {if (hasBeanFactory()) {destroyBeans();closeBeanFactory();}try {DefaultListableBeanFactory beanFactory = createBeanFactory();beanFactory.setSerializationId(getId());customizeBeanFactory(beanFactory);loadBeanDefinitions(beanFactory);synchronized (this.beanFactoryMonitor) {this.beanFactory = beanFactory;}}catch (IOException ex) {throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);}
}

关键的一个类出来了：

DefaultListableBeanFactory beanFactory = createBeanFactory();

protected DefaultListableBeanFactory createBeanFactory() {return new DefaultListableBeanFactory(getInternalParentBeanFactory());
}

在DefaultListableBeanFactory中有了很多实例变量，其中大多是集合形式，用来保存一些必要的对象。

/** Map of bean definition objects, keyed by bean name */
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(256);

存储Bean名称–>Bean定义映射关系

/** Map of singleton and non-singleton bean names, keyed by dependency type */
private final Map<Class<?>, String[]> allBeanNamesByType = new ConcurrentHashMap<Class<?>, String[]>(64);/** Map of singleton-only bean names, keyed by dependency type */
private final Map<Class<?>, String[]> singletonBeanNamesByType = new ConcurrentHashMap<Class<?>, String[]>(64);

所有单例和非单例类型和bean的名字数组映射关系

/** List of bean definition names, in registration order */
private volatile List<String> beanDefinitionNames = new ArrayList<String>(256);

所有的Bean definition name的集合

直接看AbstractXmlApplicationContext的loadBeanDefinitions

@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {// Create a new XmlBeanDefinitionReader for the given BeanFactory.XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);// Configure the bean definition reader with this context's// resource loading environment.beanDefinitionReader.setEnvironment(this.getEnvironment());beanDefinitionReader.setResourceLoader(this);beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));// Allow a subclass to provide custom initialization of the reader,// then proceed with actually loading the bean definitions.initBeanDefinitionReader(beanDefinitionReader);loadBeanDefinitions(beanDefin   itionReader);
}

创建bean的解析类：XmlBeanDefinitionReader，将bean的解析工作，交给给BeanDefinitionReader处理。

->XmlBeanDefinitionReader.loadBeanDefinitions(EncodedResource encodedResource)

->XmlBeanDefinitionReader.doLoadBeanDefinitions(InputSource inputSource, Resource resource)

->XmlBeanDefinitionReader.registerBeanDefinitions(Document doc, Resource resource)

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();int countBefore = getRegistry().getBeanDefinitionCount();documentReader.registerBeanDefinitions(doc, createReaderContext(resource));return getRegistry().getBeanDefinitionCount() - countBefore;
}

使用DefaultBeanDefinitionDocumentReader来读取并注册beanDefinition：

->DefaultBeanDefinitionDocumentReader.doRegisterBeanDefinitions(Element root)

protected void doRegisterBeanDefinitions(Element root) {BeanDefinitionParserDelegate parent = this.delegate;this.delegate = createDelegate(getReaderContext(), root, parent);if (this.delegate.isDefaultNamespace(root)) {String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);if (StringUtils.hasText(profileSpec)) {String[] specifiedProfiles = StringUtils.tokenizeToStringArray(profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {if (logger.isInfoEnabled()) {logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec +"] not matching: " + getReaderContext().getResource());}return;}}}preProcessXml(root);parseBeanDefinitions(root, this.delegate);postProcessXml(root);this.delegate = parent;}

->DefaultBeanDefinitionDocumentReader.parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate)

->DefaultBeanDefinitionDocumentReader.processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate)

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);if (bdHolder != null) {bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);try {// Register the final decorated instance.BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());}catch (BeanDefinitionStoreException ex) {getReaderContext().error("Failed to register bean definition with name '" +bdHolder.getBeanName() + "'", ele, ex);}// Send registration event.getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));}
}