本文基于spring 5.2.23.RELEASE版本分析，jar包spring-context:5.1.13.RELEASE.jar
Spring 的核心方法refresh()方法位于AbstractApplicationContext.java类中.

refresh()方法说明

加载和刷新配置的表示形式，这些配置是配置在xml文件、属性文件或者是跟数据库模式相关联的配置信息。
这是一个启动方法，如果启动失败，它将销毁已经创建的单例对象，避免资源浪费。
换句话说，在调用该方法后，应该实例化所有的单例或者不实例化所有的单例。
如果无法初始化bean工厂，则抛出BeansException异常；
如果已经初始化并且不支持多次刷新尝试，多次刷新会抛出IllegalStateException异常。

/*** Load or refresh the persistent representation of the configuration,* which might an XML file, properties file, or relational database schema.* <p>As this is a startup method, it should destroy already created singletons* if it fails, to avoid dangling resources. In other words, after invocation* of that method, either all or no singletons at all should be instantiated.* @throws BeansException if the bean factory could not be initialized* @throws IllegalStateException if already initialized and multiple refresh* attempts are not supported*/void refresh() throws BeansException, IllegalStateException;

refresh()源码

public void refresh() throws BeansException, IllegalStateException {synchronized (this.startupShutdownMonitor) {// 1、准备刷新上下文// 设置其启动日期和活动标志，以及执行任何资源的初始化prepareRefresh();// 2、告诉子类刷新内部bean工厂// 刷新各个子类的bean工厂，执行配置加载// 获取子类的bean工厂ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();// 3、准备bean工厂在上下文中使用prepareBeanFactory(beanFactory);try {// 4、允许在上下文子类中对bean工厂进行后处理.postProcessBeanFactory(beanFactory);// 5、在上下文中调用注册为bean的工厂处理器.invokeBeanFactoryPostProcessors(beanFactory);// 6、注册拦截bean创建的bean处理器registerBeanPostProcessors(beanFactory);// 7、初始化此上下文的消息源initMessageSource();// 8、初始化上下文的事件多路分发器.initApplicationEventMulticaster();// 9、在特定的上下文子类中初始化其他特殊bean.onRefresh();// 10、beans的监听器注册、检查.registerListeners();// 11、实例化所有剩余的（非延迟初始化）单例.finishBeanFactoryInitialization(beanFactory);// 12、最后一步：发布对应的事件finishRefresh();}catch (BeansException ex) {if (logger.isWarnEnabled()) {logger.warn("Exception encountered during context initialization - " +"cancelling refresh attempt: " + ex);}// 销毁所有已经创建的单例避免资源浪费destroyBeans();// 重置'active' 标志.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();}}}

prepareBeanFactory()说明

该方法的作用是配置工厂的标准上下文特征，例如上下文的类加载器和后处理器。

    /*** 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) {// 告诉内部bean工厂使用上下文的类加载器等beanFactory.setBeanClassLoader(getClassLoader());beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));// 使用上下文回调配置bean工厂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接口未在普通工厂中注册为可解析类型// MessageSource已注册（并为自动连接找到）为beanbeanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);beanFactory.registerResolvableDependency(ResourceLoader.class, this);beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);beanFactory.registerResolvableDependency(ApplicationContext.class, this);// 注册早期 后处理器，以便将内部bean检测为应用程序监听器.beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));// 检测LoadTimeWeaver并准备编织（如果发现）if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));// 为类型匹配设置临时类加载器beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));}// R注册默认环境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());}}

initApplicationEventMulticaster说明

初始化ApplicationEventMulticaster，
如果上下文中未定义，则使用SimpleApplicationEventMulticaster。

    /*** Initialize the ApplicationEventMulticaster.* Uses SimpleApplicationEventMulticaster if none defined in the context.* @see org.springframework.context.event.SimpleApplicationEventMulticaster*/protected void initApplicationEventMulticaster() {ConfigurableListableBeanFactory beanFactory = getBeanFactory();if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {this.applicationEventMulticaster =beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);if (logger.isTraceEnabled()) {logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");}}else {this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);if (logger.isTraceEnabled()) {logger.trace("No '" + APPLICATION_EVENT_MULTICASTER_BEAN_NAME + "' bean, using " +"[" + this.applicationEventMulticaster.getClass().getSimpleName() + "]");}}}

registerListeners说明

添加将ApplicationListener实现为监听器的bean。
不会影响其他侦听器，这些侦听器可以添加而不必是bean

    /*** Add beans that implement ApplicationListener as listeners.* Doesn't affect other listeners, which can be added without being beans.*/protected void registerListeners() {// Register statically specified listeners first.for (ApplicationListener<?> listener : getApplicationListeners()) {getApplicationEventMulticaster().addApplicationListener(listener);}// Do not initialize FactoryBeans here: We need to leave all regular beans// uninitialized to let post-processors apply to them!String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);for (String listenerBeanName : listenerBeanNames) {getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);}// Publish early application events now that we finally have a multicaster...Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;this.earlyApplicationEvents = null;if (earlyEventsToProcess != null) {for (ApplicationEvent earlyEvent : earlyEventsToProcess) {getApplicationEventMulticaster().multicastEvent(earlyEvent);}}}