Spring Boot 嵌入式 Servlet 容器启动原理

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

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，创建容器中的每一个组件），
如果是 WEB 应用
　　创建的是 org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext 容器；
如果不是
　　创建的是 org.springframework.web.context.ConfigurableWebApplicationContext

3）、refresh(context); 刷新上一步创建好的 IOC 容器

public void refresh() throws BeansException, IllegalStateException {
     Object var1 = this.startupShutdownMonitor;
     synchronized(this.startupShutdownMonitor) {
         this.prepareRefresh();
         ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
         this.prepareBeanFactory(beanFactory);

         try {
             this.postProcessBeanFactory(beanFactory);
             this.invokeBeanFactoryPostProcessors(beanFactory);
             this.registerBeanPostProcessors(beanFactory);
             this.initMessageSource();
             this.initApplicationEventMulticaster();
             this.onRefresh();
             this.registerListeners();
             this.finishBeanFactoryInitialization(beanFactory);
             this.finishRefresh();
         } catch (BeansException var9) {
             if (this.logger.isWarnEnabled()) {
                 this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var9);
             }

             this.destroyBeans();
             this.cancelRefresh(var9);
             throw var9;
         } finally {
             this.resetCommonCaches();
         }

     }
 }

4）、this.onRefresh(); WEB 的 IOC 容器重写了 onRefresh() 方法

5）、 WEB 的 IOC 容器会创建 嵌入式的 Servlet 容器

@Override
protected void onRefresh() {
	super.onRefresh();
	try {
		createEmbeddedServletContainer();
	}
	catch (Throwable ex) {
		throw new ApplicationContextException("Unable to start embedded container",
				ex);
	}
}

6）、获取嵌入式的Servlet容器工厂：
EmbeddedServletContainerFactory containerFactory = getEmbeddedServletContainerFactory();

private void createEmbeddedServletContainer() {
	EmbeddedServletContainer localContainer = this.embeddedServletContainer;
	ServletContext localServletContext = getServletContext();
	if (localContainer == null && localServletContext == null) {
		EmbeddedServletContainerFactory containerFactory = getEmbeddedServletContainerFactory();
		this.embeddedServletContainer = containerFactory
				.getEmbeddedServletContainer(getSelfInitializer());
	}
	else if (localServletContext != null) {
		try {
			getSelfInitializer().onStartup(localServletContext);
		}
		catch (ServletException ex) {
			throw new ApplicationContextException("Cannot initialize servlet context",
					ex);
		}
	}
	initPropertySources();
}

从 IOC 容器中获取 EmbeddedServletContainerFactory 组件；此时项目start 里面有哪个的依赖，就创建对应的对象：XXXXEmbeddedServletContainerFactory，后置处理器起作用，获取所有的定制器来定制 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());

private void createEmbeddedServletContainer() {
	EmbeddedServletContainer localContainer = this.embeddedServletContainer;
	ServletContext localServletContext = getServletContext();
	if (localContainer == null && localServletContext == null) {
		EmbeddedServletContainerFactory containerFactory = getEmbeddedServletContainerFactory();
		this.embeddedServletContainer = containerFactory
				.getEmbeddedServletContainer(getSelfInitializer());
	}
	else if (localServletContext != null) {
		try {
			getSelfInitializer().onStartup(localServletContext);
		}
		catch (ServletException ex) {
			throw new ApplicationContextException("Cannot initialize servlet context",
					ex);
		}
	}
	initPropertySources();
}

8）、嵌入式的Servlet容器创建对象并且启动

Spring Boot是先启动嵌入式的Servlet容器，再将IOC 容器中没有创建的对象获取出来

IOC容器启动创建嵌入式Servlet容器