【串线篇】spring boot嵌入式Servlet容器启动原理；

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； 获取嵌入式的Servlet容器工厂：

1）、SpringBoot应用启动运行run方法

2）、refreshContext(context);SpringBoot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 创 建 AnnotationConfigEmbeddedWebApplicationContext， 否 则 ： AnnotationConfigApplicationContext

3）、refresh(context);刷新刚才创建好的ioc容器；

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();
}
}
}

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

5）、webioc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