先看一下这里的refresh()方法
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. destroyBeans(); // Reset 'active' flag. cancelRefresh(ex); // Propagate exception to caller. throw ex; } } }
首先这个方法是同步的,以避免重复刷新。然后刷新的每个步骤,都放在单独的方法里,比较清晰,可以按顺序一个个看
首先是prepareRefresh()方法
protected void prepareRefresh() { this.startupDate = System.currentTimeMillis(); synchronized (this.activeMonitor) { this.active = true; } if (logger.isInfoEnabled()) { logger.info("Refreshing " + this); } // Initialize any placeholder property sources in the context environment initPropertySources(); // Validate that all properties marked as required are resolvable // see ConfigurablePropertyResolver#setRequiredProperties this.environment.validateRequiredProperties(); }
这个方法里做的事情不多,记录了开始时间,输出日志,另外initPropertySources()方法和validateRequiredProperties()方法一般都没有做什么事
然后是核心的obtainFreshBeanFactory()方法,这个方法是初始化BeanFactory,是整个refresh()方法的核心,其中完成了配置文件的加载、解析、注册,后面会专门详细说
这里要说明一下,ApplicationContext实现了BeanFactory接口,并实现了ResourceLoader、MessageSource等接口,可以认为是增强的BeanFactory。但是ApplicationContext并不自己重复实现BeanFactory定义的方法,而是委托给DefaultListableBeanFactory来实现。这种设计思路也是值得学习的
后面的prepareBeanFactory()、postProcessBeanFactory()、invokeBeanFactoryPostProcessors()、registerBeanPostProcessors()、initMessageSource()、initApplicationEventMulticaster()、onRefresh()、registerListeners()、finishBeanFactoryInitialization()、finishRefresh()等方法,是添加一些后处理器、广播、拦截器等,就不一个个细说了。
其中的关键方法是finishBeanFactoryInitialization(),在这个方法中,会对刚才注册的Bean(不延迟加载的),进行实例化,所以也是一个核心方法
从整体上介绍完了流程,接下来就重点看obtainFreshBeanFactory()方法,上文说到,在这个方法里,完成了配置文件的加载、解析、注册
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() { refreshBeanFactory(); ConfigurableListableBeanFactory beanFactory = getBeanFactory(); if (logger.isDebugEnabled()) { logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory); } return beanFactory; }
这个方法做了2件事,首先通过refreshBeanFactory()方法,创建了DefaultListableBeanFactory的实例,并进行初始化。然后返回
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); } }
首先如果已经有BeanFactory实例,就先清空。
然后通过createBeanFactory()方法,创建一个DefaultListableBeanFactory的实例
protected DefaultListableBeanFactory createBeanFactory() { return new DefaultListableBeanFactory(getInternalParentBeanFactory()); }
接下来设置ID唯一标识
beanFactory.setSerializationId(getId());
然后允许用户进行一些自定义的配置
protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) { if (this.allowBeanDefinitionOverriding != null) { beanFactory.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding); } if (this.allowCircularReferences != null) { beanFactory.setAllowCircularReferences(this.allowCircularReferences); } beanFactory.setAutowireCandidateResolver(new QualifierAnnotationAutowireCandidateResolver()); }
最后,就是核心的loadBeanDefinitions()方法
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(beanDefinitionReader); }
这里首先会创建一个XmlBeanDefinitionReader的实例,然后进行初始化
// 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);
这里要说明一下,ApplicationContext并不自己负责配置文件的加载、解析、注册,而是将这些工作委托给XmlBeanDefinitionReader来做。
loadBeanDefinitions(beanDefinitionReader);
这行代码,就是Bean定义读取实际发生的地方。这里的工作,主要是XmlBeanDefinitionReader来完成的,下一篇博客会详细介绍这个过程