初始化基本流程

SpringApplication的prepareContext准备上下文

这里面有干了很多事，他会将最前面获得的初始化器都初始化，然后广播上下文准备好事件，然后这里居然还设置了不能覆盖同名bean定义，这样就避免了用户去捣乱了。最后会把启动类的注册到bean定义里，然后广播上下文加载完成事件。

private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment,SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {context.setEnvironment(environment);//配置环境postProcessApplicationContext(context);//一些设置处理applyInitializers(context);//初始化监听器进行初始化listeners.contextPrepared(context);//广播上下文准备好的事件ApplicationContextInitializedEventif (this.logStartupInfo) {//控制台打启动信息logStartupInfo(context.getParent() == null);logStartupProfileInfo(context);}// Add boot specific singleton beansConfigurableListableBeanFactory beanFactory = context.getBeanFactory();beanFactory.registerSingleton("springApplicationArguments", applicationArguments);if (printedBanner != null) {beanFactory.registerSingleton("springBootBanner", printedBanner);}if (beanFactory instanceof DefaultListableBeanFactory) {((DefaultListableBeanFactory) beanFactory)//不允许同名的bean定义的覆盖.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);}if (this.lazyInitialization) {context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());}// Load the sourcesSet<Object> sources = getAllSources();//获取启动源集合，就是传给SpringApplication的参数类Assert.notEmpty(sources, "Sources must not be empty");load(context, sources.toArray(new Object[0]));//注册启动类的bean定义listeners.contextLoaded(context);//广播上下文加载完成事件ApplicationPreparedEvent}

postProcessApplicationContext处理

就是提前去注册bean名字生成器，资源加载器，还有前面创建的转换器也要放进来。

	protected void postProcessApplicationContext(ConfigurableApplicationContext context) {if (this.beanNameGenerator != null) {context.getBeanFactory().registerSingleton(AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR,this.beanNameGenerator);}if (this.resourceLoader != null) {if (context instanceof GenericApplicationContext) {((GenericApplicationContext) context).setResourceLoader(this.resourceLoader);}if (context instanceof DefaultResourceLoader) {((DefaultResourceLoader) context).setClassLoader(this.resourceLoader.getClassLoader());}}if (this.addConversionService) {//添加转换器context.getBeanFactory().setConversionService(ApplicationConversionService.getSharedInstance());}}

applyInitializers初始化器初始化

获取最开始创建的初始化器，遍历每一个初始化器，进行初始化。

	protected void applyInitializers(ConfigurableApplicationContext context) {for (ApplicationContextInitializer initializer : getInitializers()) {Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(initializer.getClass(),ApplicationContextInitializer.class);//获取ApplicationContextInitializer接口的泛型类型Assert.isInstanceOf(requiredType, context, "Unable to call initializer.");//context不是requiredType类型是不行的initializer.initialize(context);//初始化}}

load

创建bean定义加载器，进行bean定义的加载，就是把sources注册到bean定义里。

protected void load(ApplicationContext context, Object[] sources) {if (logger.isDebugEnabled()) {logger.debug("Loading source " + StringUtils.arrayToCommaDelimitedString(sources));}BeanDefinitionLoader loader = createBeanDefinitionLoader(getBeanDefinitionRegistry(context), sources);if (this.beanNameGenerator != null) {loader.setBeanNameGenerator(this.beanNameGenerator);}if (this.resourceLoader != null) {loader.setResourceLoader(this.resourceLoader);}if (this.environment != null) {loader.setEnvironment(this.environment);}loader.load();}//遍历每一个加载int load() {int count = 0;for (Object source : this.sources) {count += load(source);}return count;}

根据不同类型加载，最后都是registerBean：

SpringApplication的refreshContext刷新上下文

除了刷新外，还注册了一个钩子

	private void refreshContext(ConfigurableApplicationContext context) {refresh(context);if (this.registerShutdownHook) {try {context.registerShutdownHook();}catch (AccessControlException ex) {// Not allowed in some environments.}}}

refresh

调用当前上下文AbstractApplicationContext类型的refresh，当前上下文是ServletWebServerApplicationContext类型的，所以会调用到他的refresh。

	protected void refresh(ApplicationContext applicationContext) {Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);((AbstractApplicationContext) applicationContext).refresh();}

ServletWebServerApplicationContext的refresh

然后他又调用父类的refresh。

	@Overridepublic final void refresh() throws BeansException, IllegalStateException {try {super.refresh();}catch (RuntimeException ex) {stopAndReleaseWebServer();throw ex;}}

里面就是spring的refresh方法，进行初始化，就不讲了，可以看我写的spring源码文章，其实内部干了不少事情，后面会讲，毕竟前面那么多初始化器初始化了，肯定会对后面spring初始化有所作用。
看看钩子方法，其实就是注册一个关闭线程：

刷新完成后基本没啥事了，就进行启动完成事件通知，还有一些的ApplicationRunner和CommandLineRunner类型的bean要处理，一般是没有的：

最后再通知一个运行事件初始化就完成了：