【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