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 Spring's 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DefaultListableBeanFactory，XmlBeanFactory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 context's 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