springboot中如何嵌入servlet容器以及容器启动过程

  最近在学习springboot，抽空记录一下，加强记忆。

springboot兼容Tomcat，jetty，undertow容器，默认兼容Tomcat容器，因为spring-boot-starter-web包含tomcat，因此需要使用的时候，需要先把tomcat排除，再引入其他容器，如下：

	org.springframework.boot
	spring-boot-starter-web
	
		
			spring-boot-starter-tomcat
			org.springframework.boot
		
	


	spring-boot-starter-jetty
	org.springframework.boot

 现在分成2部分，容器注入方式和容器使用

1. ServletWebServerFactoryConfiguration是配置类，里面的@Bean会被自动注入到spring容器中，通过@ConditionalOnClass来判断应该注入哪个servlet容器

   @Configuration(proxyBeanMethods = false)
   @ConditionalOnClass({ Servlet.class, Tomcat.class, UpgradeProtocol.class })//如果系统中存在tomcat相关类，引入tomcat内嵌servlet容器
   @ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
   static class EmbeddedTomcat {
   //自动注入TomcatServletWebServerFactory
   @Bean
   TomcatServletWebServerFactory tomcatServletWebServerFactory(ObjectProvider connectorCustomizers,ObjectProvider contextCustomizers,
   		ObjectProvider> protocolHandlerCustomizers) {
   	TomcatServletWebServerFactory factory = new TomcatServletWebServerFactory();
   	factory.getTomcatConnectorCustomizers().addAll(connectorCustomizers.orderedStream().collect(Collectors.toList()));
   	factory.getTomcatContextCustomizers().addAll(contextCustomizers.orderedStream().collect(Collectors.toList()));
   	factory.getTomcatProtocolHandlerCustomizers().addAll(protocolHandlerCustomizers.orderedStream().collect(Collectors.toList()));
   	return factory;
   }
   
   
   @Configuration(proxyBeanMethods = false)
   @ConditionalOnClass({ Servlet.class, Server.class, Loader.class, WebAppContext.class })//如果系统中存在Jetty相关类，引入Jetty内嵌servlet容器
   @ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
   static class EmbeddedJetty {

   2.springBoot启动时通过SpringApplication.run方法，最终调用onRefresh()方法,取得TomcatServletWebServerFactory，启动容器

   @Override
   protected void onRefresh() {
   	super.onRefresh();
   	try {
   		createWebServer();//创建servlet容器
   	}
   	catch (Throwable ex) {
   		throw new ApplicationContextException("Unable to start web server", ex);
   	}
   }
   
   private void createWebServer() {
   	WebServer webServer = this.webServer;
   	ServletContext servletContext = getServletContext();
   	if (webServer == null && servletContext == null) {
   		ServletWebServerFactory factory = getWebServerFactory();
   		this.webServer = factory.getWebServer(getSelfInitializer());
   	}
   	else if (servletContext != null) {
   		try {
   			getSelfInitializer().onStartup(servletContext);
   		}
   		catch (ServletException ex) {
   			throw new ApplicationContextException("Cannot initialize servlet context", ex);
   		}
   	}
   	initPropertySources();
   }
   
   protected ServletWebServerFactory getWebServerFactory() {
   	// Use bean names so that we don't consider the hierarchy
   	//ServletWebServerFactory.class的实现类正是：TomcatServletWebServerFactory，JettyServletWebServerFactory，UndertowServletWebServerFactory
   	String[] beanNames = getBeanFactory().getBeanNamesForType(ServletWebServerFactory.class);
   	if (beanNames.length == 0) {
   		throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to missing "
   				+ "ServletWebServerFactory bean.");
   	}
   	if (beanNames.length > 1) {
   		throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to multiple "
   				+ "ServletWebServerFactory beans : " + StringUtils.arrayToCommaDelimitedString(beanNames));
   	}
   	return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
   }