AbstractApplicationContext一个抽象应用程序上下文，主要实现了上下文初始化的功能，如：定义了初始化BeanFactory，初始化一些BeanFactoryPostProcessors，初始化MessageSource（国际化），还要一些事件广播器ApplicationEventMulticaster等等
AbstractApplicationContext因为是抽象类，其实其中一些初始化操作还是交个子类实现，如初始化BeanFactory，在AbstractApplicationContext只是做了简单的定义，具体实现还是交个子类。子类根据实际情况选择使用那种BeanFactory并进行初始化。
ApplicationContext是一个比BeanFactory更具丰富IOC容器接口，而AbstractApplicationContext是其的一个抽象实现，定义和实现了一系列的初始化流程。
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
//准备上下文刷新
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
//这里创建BeanFactory，具体逻辑交个子类实现（不同的上下文使用不同的BeanFactory）
//加载逻辑还是基本通过BeanDefinitionReader去加载BeanDefinition并注册到BeanFactory中
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
//为BeanFactory在上下文中使用做准备（其实是给BeanFactory配置一些信息）
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
//调用各种BeanFactoryPostProcessor(可以实现BeanFactoryPostProcessor接口制作工厂后置处理器)
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
//注册BeanPostProcessors
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
//初始化MessageSource（国际化）
initMessageSource();
// Initialize event multicaster for this context.
//初始化事件广播器
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
//空实现，交给子类实现，具体是让子类如何刷新上下文
onRefresh();
// Check for listener beans and register them.
//注册监听器
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();
}
}
}
/**
* Tell the subclass to refresh the internal bean factory.
* @return the fresh BeanFactory instance
* @see #refreshBeanFactory()
* @see #getBeanFactory()
*/
//
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
//空实现，具体交给子类实现（因为不同子类根据实际情况用不同的BeanFactory,所以具体实现交个子类）
refreshBeanFactory();
return getBeanFactory();
}
该方法主要用于配置BeanFactory，如：配置BeanClassLoader，配置BeanPostProcessor，忽略一些依赖接口，配置一些环境Bean等等
/**
* Configure the factory's standard context characteristics,
* such as the context's ClassLoader and post-processors.
* @param beanFactory the BeanFactory to configure
*/
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader etc.
beanFactory.setBeanClassLoader(getClassLoader());
//这里增加了SPEL语言支持（使得能解析#{bean.xxx}相关形式的属性值）
//这玩意会在解析Bean时用到
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// Configure the bean factory with context callbacks.
//忽略接口，添加BeanPostProcessor
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
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.
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.
//这里增加对AspectJ的支持
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.
//注册环境bean
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());
}
}