spring源码解析（容器的功能扩展）

Spring中还提供了另一个接口ApplicationContext继承了BeanFactory且包含BeanFactory的所有功能并额外提供了一些其他的功能。比如国际化支持、事件机制、AOP支持等等。通过ApplicationContext加载xml文件public static void main(String[] args) { ApplicationContext applicationContext new ClassPathXmlApplicationContext(beans.xml); }进入构造器后主要有两个逻辑public ClassPathXmlApplicationContext( String[] configLocations, boolean refresh, Nullable ApplicationContext parent) throws BeansException { super(parent); setConfigLocations(configLocations);//设置配置路径并支持多个配置文件 if (refresh) { refresh(); } }在setConfigLocations中对路径做了解析比如${var}这样的会从环境变量中取到var的变量进行替换而refresh中基本上包含了ApplicationContext的全部功能。public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // 刷新上下文环境可通过重写initPropertySource设置环境变量 prepareRefresh(); // Tell the subclass to refresh the internal bean factory. // 初始化BeanFactory并进行xml文件读取 ConfigurableListableBeanFactory beanFactory obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. // 对BeanFactory进行各种功能填充 prepareBeanFactory(beanFactory); try { // 空实现可有子类实现提供扩展能力 // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory); // 激活各种BeanFactoryPostProcessors处理器 // Invoke factory processors registered as beans in the context. invokeBeanFactoryPostProcessors(beanFactory); // 注册BeanPostProcessors处理器 // Register bean processors that intercept bean creation. registerBeanPostProcessors(beanFactory); // 国际化支持初始化MessageSource // Initialize message source for this context. initMessageSource(); // 初始化事件广播器用于通知事件Listener // Initialize event multicaster for this context. initApplicationEventMulticaster(); // 空实现由子类实现 // Initialize other special beans in specific context subclasses. onRefresh(); // 查找所有注册的Listener注册到广播器中 // Check for listener beans and register them. registerListeners(); // 初始化生下的单实例非惰性 // Instantiate all remaining (non-lazy-init) singletons. finishBeanFactoryInitialization(beanFactory); // 完成刷新过程并触发ContextRefreshEvent事件通知通知生命周期处理器刷新过程 // 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 Springs core, since we // might not ever need metadata for singleton beans anymore... resetCommonCaches(); } } }在refresh中逻辑还是很多的根据代码块里添加了中文注释的地方逐步解释在prepareRefresh中是做环境的准备的环境变量的初始化以及系统属性的验证可以通过实现initPropertySource方法进行环境变量的赋值操作等protected void prepareRefresh() { // Initialize any placeholder property sources in the context environment. initPropertySources(); // Validate that all properties marked as required are resolvable: // see ConfigurablePropertyResolver#setRequiredProperties getEnvironment().validateRequiredProperties(); }接下来就是加载BeanFactory了前面已经知道默认是使用XmlBeanDefinitionReader来读取xml的protected ConfigurableListableBeanFactory obtainFreshBeanFactory() { refreshBeanFactory(); return getBeanFactory(); } 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); } }实例化DefaultListableBeanFactoryXmlBeanFactory就是继承DefaultListableBeanFactory的在customizeBeanFactory中对BeanFactory进行了定制设置是否允许覆盖同名对象以及是否允许循环依赖并设置支持注解的解析器 QualifierAnnotaionAutowireCandidateResolver在loadBeanDefinitions中就是比较熟悉的了指定XmlBeanDefinitionReader为解析器开始执行xml的解析了。回到前面主流程中接下来是对prepareBeanFacctory进行功能的填充protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) { // Tell the internal bean factory to use the contexts class loader etc. beanFactory.setBeanClassLoader(getClassLoader()); // 设置表达式语言的解析器提供对SPEL语言的支持 beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader())); // 增加属性编辑器 beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment())); // Configure the bean factory with context callbacks. // 在bean初始化后对实现Aware接口的实例提供一些资源 beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this)); // 忽略依赖 beanFactory.ignoreDependencyInterface(EnvironmentAware.class); beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class); beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class); beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class); beanFactory.ignoreDependencyInterface(MessageSourceAware.class); beanFactory.ignoreDependencyInterface(ApplicationContextAware.class); // BeanFactory interface not registered as resolvable type in a plain factory. // MessageSource registered (and found for autowiring) as a bean. // 注册依赖 beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory); beanFactory.registerResolvableDependency(ResourceLoader.class, this); beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this); beanFactory.registerResolvableDependency(ApplicationContext.class, this); // Register early post-processor for detecting inner beans as ApplicationListeners. beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this)); // Detect a LoadTimeWeaver and prepare for weaving, if found. if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) { beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory)); // Set a temporary ClassLoader for type matching. beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader())); } // Register default environment beans. if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) { beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment()); } if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) { beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties()); } if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) { beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment()); } }在setBeanExproeeionResolver中设置了SPEL支持的解析器比如可以通过#{var}这种方式取值在bean进行属性填充的时候会通过这个解析器完成解析在addPropertyEditorRegistrar中增加了属性注册编辑器在ResourceEditorRegistrar中的registerCustomEditors中注册了一系列常用类型的属性编辑器而ResourceEditorRegistrar是通过在AbstractBeanFactory中开始调用的如下代码protected void initBeanWrapper(BeanWrapper bw) { bw.setConversionService(getConversionService()); registerCustomEditors(bw); } protected void registerCustomEditors(PropertyEditorRegistry registry) { PropertyEditorRegistrySupport registrySupport (registry instanceof PropertyEditorRegistrySupport ? (PropertyEditorRegistrySupport) registry : null); if (registrySupport ! null) { registrySupport.useConfigValueEditors(); } if (!this.propertyEditorRegistrars.isEmpty()) { for (PropertyEditorRegistrar registrar : this.propertyEditorRegistrars) { try { // 遍历属性编辑器注册自定义编辑器 registrar.registerCustomEditors(registry); } catch (BeanCreationException ex) { Throwable rootCause ex.getMostSpecificCause(); if (rootCause instanceof BeanCurrentlyInCreationException) { BeanCreationException bce (BeanCreationException) rootCause; String bceBeanName bce.getBeanName(); if (bceBeanName ! null isCurrentlyInCreation(bceBeanName)) { if (logger.isDebugEnabled()) { logger.debug(PropertyEditorRegistrar [ registrar.getClass().getName() ] failed because it tried to obtain currently created bean ex.getBeanName() : ex.getMessage()); } onSuppressedException(ex); continue; } } throw ex; } } } if (!this.customEditors.isEmpty()) { this.customEditors.forEach((requiredType, editorClass) - registry.registerCustomEditor(requiredType, BeanUtils.instantiateClass(editorClass))); } }接下来是addBeanPostProcessor类ApplicationContextAwareProcessor实现了BeanPostProcessor接口即会在bean实例化时候调用的在postProcessBeforeInitialization中的invokeAwareInterfaces中使实现了Aware接口的bean在被初始化之后可以取得一些资源回到主流程在功能填充后即激活BeanFactoryPostProcessor,这个接口和BeanPostProcessor类似 BeanFactoryPostProcessor作用域范围是容器级的允许在容器实际实例化任何其他的bean之前读取配置元数据。典型的应用是PropertyPlaceholderConfigure在实例化bean之前会将 ${}格式进行变量替换。注册BeanPostProcessor, 按照排序顺序进行注册且重复注册情况会先移除在重新注册保证beanPostProcessor的唯一性在bean实例化阶段进行调用在初始化消息 initMessageSource中首先会查找已经定义的messageSource的bean,如果没有则使用默认的DelegationMessageSource并注册到beanFactory中初始化事件广播器和初始化消息差不多去查找applicationEventMulticater的bean,否则使用默认的SimpleApplicationEventMulticater在multicasstEvent中会遍历event的listener进行通知观察者模式的典型应用。初始化广播器后则是注册所有listener来接收广播器的通知即所有实现了ApplicationListener的bean对于单例的bean非lazy的在ApplicationContext中会默认初始化在preInstantiateSingletons中对单例的且非lazy的bean进行加载即调用getBean方法。在finishrefresh中开始生命周期通过实现Lifecycle接口可以在生命周期开始时加载start方法在最后会推送ContextRefreshEvent事件通知