spring的refresh（）

refresh()方法是spring的核心，在其中完成了容器的初始化

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) {
                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();
            }
        }
    }

1、prepareRefresh();
容器刷新前的准备，设置上下文状态，获取属性，验证必要的属性等

2、ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
获取新的beanFactory，销毁原有beanFactory、为每个bean生成BeanDefinition等

3、prepareBeanFactory(beanFactory);
配置标准的beanFactory，设置ClassLoader，设置SpEL表达式解析器等

4、postProcessBeanFactory(beanFactory);
模板方法，允许在子类中对beanFactory进行后置处理。

5、invokeBeanFactoryPostProcessors(beanFactory);
实例化并调用所有注册的beanFactory后置处理器（实现接口BeanFactoryPostProcessor的bean，在beanFactory标准初始化之后执行）。
例如:
PropertyPlaceholderConfigurer(处理占位符)

6、registerBeanPostProcessors(beanFactory);
实例化和注册beanFactory中扩展了BeanPostProcessor的bean。
例如：
AutowiredAnnotationBeanPostProcessor(处理被@Autowired注解修饰的bean并注入)
RequiredAnnotationBeanPostProcessor(处理被@Required注解修饰的方法)
CommonAnnotationBeanPostProcessor(处理@PreDestroy、@PostConstruct、@Resource等多个注解的作用)等。

7、initMessageSource();
初始化国际化工具类MessageSource

8、initApplicationEventMulticaster();
初始化时间广播器

9、onRefresh();
模板方法，在容器刷新的时候可以自定义逻辑，不同的Spring容器做不同的事情。

10、registerListeners();
注册监听器，广播early application events

11、finishBeanFactoryInitialization(beanFactory);
实例化所有剩余的（非懒加载）单例
比如invokeBeanFactoryPostProcessors方法中根据各种注解解析出来的类，在这个时候都会被初始化。
实例化的过程各种BeanPostProcessor开始起作用。

12、finishRefresh();
refresh做完之后需要做的其他事情。
清除上下文资源缓存（如扫描中的ASM元数据）
初始化上下文的生命周期处理器，并刷新（找出Spring容器中实现了Lifecycle接口的bean并执行start()方法）。
发布ContextRefreshedEvent事件告知对应的ApplicationListener进行响应的操作