Spring ApplicationContext refresh方法解读(一)

上节中已经讲过AnnotationConfigApplicationContext中初始化了reader,用于加载6个Bean。主要是Processor，我们称之为后置处理器。处理器主要的使用就是在refresh方法中。

refresh方法

refresh方法是Spring ApplicationContext的精髓，ioc,aop都是在此中完成。此方法是在AbstractApplicationContext实现的，子类可以覆盖重写父类中的方法。例如Spring Boot中ServletWebServerApplicationContext 就是覆盖了onRefresh方法，完成refresh方法后启动webServer的功能。
通过阅读refresh方法，可以看出通过使用synchronized加锁，调用类内不同的方法，完成以下工作：属性配置注入，BeanFactory准备，BeanFactory后置处理器调用，注册beanPostProcessor，初始化国际化及事件注册器，完成BeanFactory,完成refresh方法。

@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			////准备工作包括设置启动时间，是否激活标识位，
			// 初始化属性源(property source)配置
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			//返回一个factory 为什么需要返回一个工厂
			//因为要对工厂进行初始化
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			//准备工厂
			prepareBeanFactory(beanFactory);

			try {
				// Allows post-processing of the bean factory in context subclasses.
				// org.springframework.web.context.support.GenericWebApplicationContext.postProcessBeanFactory
				// org.springframework.web.context.support.StaticWebApplicationContext.postProcessBeanFactory
				//这个方法在当前版本的spring是没用任何代码的
				//可能spring期待在后面的版本中去扩展吧
				postProcessBeanFactory(beanFactory);

				// Invoke factory processors registered as beans in the context.
				//在spring的环境中去执行已经被注册的 factory processors
				//设置执行自定义的ProcessBeanFactory 和spring内部自己定义的
				invokeBeanFactoryPostProcessors(beanFactory);

				// Register bean processors that intercept bean creation.
				//注册beanPostProcessor
				registerBeanPostProcessors(beanFactory);

				// Initialize message source for this context.
				initMessageSource();

				// Initialize event multicaster for this context.
				//初始化应用事件广播器
				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();
			}
		}
	}