@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication
@Import(BeanPostProcessorsRegistrar.class)
//導(dǎo)入BeanPostProcessorsRegistrar：Spring注解版；給容器中導(dǎo)入一些組件
//導(dǎo)入了EmbeddedServletContainerCustomizerBeanPostProcessor：
//后置處理器：bean初始化前后（創(chuàng)建完對(duì)象，還沒賦值賦值）執(zhí)行初始化工作
public class EmbeddedServletContainerAutoConfiguration { 
        .....    
        @Configuration
	@ConditionalOnClass({ Servlet.class, Tomcat.class })//判斷當(dāng)前是否引入了Tomcat依賴；
	@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)//判斷當(dāng)前容器沒有用戶自己定義EmbeddedServletContainerFactory：嵌入式的Servlet容器工廠；作用：創(chuàng)建嵌入式的Servlet容器
	public static class EmbeddedTomcat { 
		@Bean
		public TomcatEmbeddedServletContainerFactory tomcatEmbeddedServletContainerFactory() {
			return new TomcatEmbeddedServletContainerFactory();
		} 
	}    
    /**
	 * Nested configuration if Jetty is being used.
	 */
	@Configuration
	@ConditionalOnClass({ Servlet.class, Server.class, Loader.class,
			WebAppContext.class })
	@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
	public static class EmbeddedJetty {
 
		@Bean
		public JettyEmbeddedServletContainerFactory jettyEmbeddedServletContainerFactory() {
			return new JettyEmbeddedServletContainerFactory();
		} 
	} 
	/**
	 * Nested configuration if Undertow is being used.
	 */
	@Configuration
	@ConditionalOnClass({ Servlet.class, Undertow.class, SslClientAuthMode.class })
	@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
	public static class EmbeddedUndertow {
 
		@Bean
		public UndertowEmbeddedServletContainerFactory undertowEmbeddedServletContainerFactory() {
			return new UndertowEmbeddedServletContainerFactory();
		} 
	}

public interface EmbeddedServletContainerFactory {
 
   //獲取嵌入式的Servlet容器
   EmbeddedServletContainer getEmbeddedServletContainer(
         ServletContextInitializer... initializers);
}

@Override
public EmbeddedServletContainer getEmbeddedServletContainer(
      ServletContextInitializer... initializers) {
    //創(chuàng)建一個(gè)Tomcat
   Tomcat tomcat = new Tomcat();
    
    //配置Tomcat的基本環(huán)節(jié)
   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);
    
    //將配置好的Tomcat傳入進(jìn)去，返回一個(gè)EmbeddedServletContainer；并且啟動(dòng)Tomcat服務(wù)器
   return getTomcatEmbeddedServletContainer(tomcat);
}

//初始化之前
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName)
      throws BeansException {
    //如果當(dāng)前初始化的是一個(gè)ConfigurableEmbeddedServletContainer類型的組件
   if (bean instanceof ConfigurableEmbeddedServletContainer) {
       //
      postProcessBeforeInitialization((ConfigurableEmbeddedServletContainer) bean);
   }
   return bean;
} 
private void postProcessBeforeInitialization(
			ConfigurableEmbeddedServletContainer bean) {
    //獲取所有的定制器，調(diào)用每一個(gè)定制器的customize方法來(lái)給Servlet容器進(jìn)行屬性賦值；
    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
            //從容器中獲取所有這葛類型的組件：EmbeddedServletContainerCustomizer
            //定制Servlet容器，給容器中可以添加一個(gè)EmbeddedServletContainerCustomizer類型的組件
            .getBeansOfType(EmbeddedServletContainerCustomizer.class,
                            false, false)
            .values());
        Collections.sort(this.customizers, AnnotationAwareOrderComparator.INSTANCE);
        this.customizers = Collections.unmodifiableList(this.customizers);
    }
    return this.customizers;
} 
//ServerProperties也是定制器