@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)

@Configuration

@ConditionalOnWebApplication  //如果是web应用，当前配置类生效

@Import(BeanPostProcessorsRegistrar.class) //Bean后置处理器的注册器；给容器中注入一些组件
//导入了EmbeddedServletContainerCustomizerBeanPostProcessor
//后置处理器功能：在bean初始化前后（刚创建完对象，还没属性赋值）执行初始化工作

public class EmbeddedServletContainerAutoConfiguration {

    /**

     * Nested configuration if Tomcat is being used.

     */

    @Configuration

    @ConditionalOnClass({ Servlet.class, Tomcat.class }) //判断当前是否引入了Tomcat依赖；

    @ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)  //判断当前容器没有
用户自定义的EmbeddedServletContainerFactory（嵌入式servlet容器工厂）；作用：创建servlet容器；
　　　　

    public static class EmbeddedTomcat {

        @Bean

        public TomcatEmbeddedServletContainerFactory tomcatEmbeddedServletContainerFactory() {

            return new TomcatEmbeddedServletContainerFactory();

        }

    }

public interface EmbeddedServletContainerFactory {
　　　　//获取嵌入式servlet容器

    EmbeddedServletContainer getEmbeddedServletContainer(ServletContextInitializer... var1);

}

    @Override

    public EmbeddedServletContainer getEmbeddedServletContainer(

            ServletContextInitializer... initializers) {
　　　　　　// 创建Tomcat

        Tomcat tomcat = new Tomcat();
　　　　　　//配置Tomcat的基本环境

        File baseDir = (this.baseDirectory != null ? this.baseDirectory

                : createTempDir("tomcat"));

        tomcat.setBaseDir(baseDir.getAbsolutePath());

        Connector connector = new Connector(this.protocol);

        tomcat.getService().addConnector(connector);

        customizeConnector(connector);

        tomcat.setConnector(connector);

        tomcat.getHost().setAutoDeploy(false);

        configureEngine(tomcat.getEngine());

        for (Connector additionalConnector : this.additionalTomcatConnectors) {

            tomcat.getService().addConnector(additionalConnector);

        }

        prepareContext(tomcat.getHost(), initializers);
　　　　　　//将配置好的Tomcat传入进去。返回一个EmbeddedServletContainer 并且启动tomcat容器

        return getTomcatEmbeddedServletContainer(tomcat);

    }

ServerPorperties ,EmbeddedServletContainerCustomizer

//初始化之前   
 @Override

    public Object postProcessBeforeInitialization(Object bean, String beanName)

            throws BeansException {
　　　　　　//如果当前初始化的是一个ConfigurableEmbeddedServletContainer类型的组件

        if (bean instanceof ConfigurableEmbeddedServletContainer) {

            postProcessBeforeInitialization((ConfigurableEmbeddedServletContainer) bean);

        }

        return bean;

    }

private void postProcessBeforeInitialization(
      ConfigurableEmbeddedServletContainer bean) {
　　//获取所有的定制器，调用每一个定制器的customize()方法来给servlet容器进行属性赋值
   for (EmbeddedServletContainerCustomizer customizer : getCustomizers()) {
      customizer.customize(bean);
   }
}
private Collection<EmbeddedServletContainerCustomizer> getCustomizers() {

   if (this.customizers == null) {
      // Look up does not include the parent context
      this.customizers = new ArrayList<EmbeddedServletContainerCustomizer>(
            this.beanFactory
　　　　　　　　//从容器中获取所有这个类型的组件：EmbeddedServletContainerCustomizer
　　　　　　　　//如果要定制一个servlet容器，向容器中添加一个EmbeddedServletContainerCustomizer组件
                  .getBeansOfType(EmbeddedServletContainerCustomizer.class,
                        false, false)
                  .values());
      Collections.sort(this.customizers, AnnotationAwareOrderComparator.INSTANCE);
      this.customizers = Collections.unmodifiableList(this.customizers);
   }
   return this.customizers;
}

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();

            }

        }

    }