什么时候创建嵌入式的Servlet容器工厂？什么时候获取嵌入式的Servlet容器并启动Tomcat？

    1、Spring Boot应用启动运行run方法

    2、refreshContext(context)：Spring Boot刷新IOC容器（创建IOC容器对象，并初始化容器，创建容器中的每一个组件）。如果是web应用则创建AnnotationConfigEmbeddedWebApplicationContext，如果不是web应用则创建AnnotationConfigApplicationContext。

    3、refresh(context)：刷新刚才创建好的IOC容器

    1. public void refresh() throws BeansException, IllegalStateException {
    2.        synchronized (this.startupShutdownMonitor) {
    3.           // Prepare this context for refreshing.
    4.         prepareRefresh();
    5.           // Tell the subclass to refresh the internal bean factory.
    6.           ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
    7.           // Prepare the bean factory for use in this context.
    8.           prepareBeanFactory(beanFactory);
    9.           try {
    10.              // Allows post-processing of the bean factory in context subclasses.
    11.              postProcessBeanFactory(beanFactory);
    12.              // Invoke factory processors registered as beans in the context.
    13.              invokeBeanFactoryPostProcessors(beanFactory);
    14.              // Register bean processors that intercept bean creation.
    15.              registerBeanPostProcessors(beanFactory);
    16.              // Initialize message source for this context.
    17.              initMessageSource();
    18.              // Initialize event multicaster for this context.
    19.              initApplicationEventMulticaster();
    20.              // Initialize other special beans in specific context subclasses.
    21.              onRefresh();
    22.              // Check for listener beans and register them.
    23.              registerListeners();
    24.              // Instantiate all remaining (non-lazy-init) singletons.
    25.              finishBeanFactoryInitialization(beanFactory);
    26.              // Last step: publish corresponding event.
    27.              finishRefresh();
    29.         } catch (BeansException ex) {
    30.             if (logger.isWarnEnabled()) {
    31.                 logger.warn("Exception encountered during context initialization - " +
    32.                                           "cancelling refresh attempt: " + ex);
    33.              }
    34.              // Destroy already created singletons to avoid dangling resources.
    35.              destroyBeans();
    36.              // Reset 'active' flag.
    37.              cancelRefresh(ex);
    38.              // Propagate exception to caller.
    39.              throw ex;
    41.         } finally {
    42.          // Reset common introspection caches in Spring's core, since we
    43.          // might not ever need metadata for singleton beans anymore...
    44.          resetCommonCaches();
    45.       }
    46.    }
    47. }

    4、onRefresh()：web的ioc容器重写了onRefresh方法

    5、web ioc容器会创建嵌入式的Servlet容器，createEmbeddedServletContainer()

    6、获取嵌入式的Servlet容器工厂：
    EmbeddedServletContainerFactory containerFactory = getEmbeddedServletContainerFactory()
    从ioc容器中获取EmbeddedServletContainerFactory组件，TomcatEmbeddedServletContainerFactory创建对象，后置处理器一看是这个对象，就获取所有的定制器来先定制Servlet容器的相关配置。

    7、使用容器工厂获取嵌入式的Servlet容器：this.embeddedServletContainer = containerFactory .getEmbeddedServletContainer(getSelfInitializer())

    8、嵌入式的Servlet容器创建对象并启动Servlet容器，先启动嵌入式的Servlet容器，再将ioc容器中剩下没有创建出的对象获取出来。

    IOC容器启动创建嵌入式的Servlet容器