springboot中如何嵌入servlet容器以及容器啓動過程

  最近在學習springboot，抽空記錄一下，加強記憶。

springboot兼容Tomcat，jetty，undertow容器，默認兼容Tomcat容器，因爲spring-boot-starter-web包含tomcat，因此需要使用的時候，需要先把tomcat排除，再引入其他容器，如下：

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-web</artifactId>
	<exclusions>
		<exclusion>
			<artifactId>spring-boot-starter-tomcat</artifactId>
			<groupId>org.springframework.boot</groupId>
		</exclusion>
	</exclusions>
</dependency>
<dependency>
	<artifactId>spring-boot-starter-jetty</artifactId>
	<groupId>org.springframework.boot</groupId>
</dependency>

 現在分成2部分，容器注入方式和容器使用

1. ServletWebServerFactoryConfiguration是配置類，裏面的@Bean會被自動注入到spring容器中，通過@ConditionalOnClass來判斷應該注入哪個servlet容器

   @Configuration(proxyBeanMethods = false)
   @ConditionalOnClass({ Servlet.class, Tomcat.class, UpgradeProtocol.class })//如果系統中存在tomcat相關類，引入tomcat內嵌servlet容器
   @ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
   static class EmbeddedTomcat {
   //自動注入TomcatServletWebServerFactory
   @Bean
   TomcatServletWebServerFactory tomcatServletWebServerFactory(ObjectProvider<TomcatConnectorCustomizer> connectorCustomizers,ObjectProvider<TomcatContextCustomizer> contextCustomizers,
   		ObjectProvider<TomcatProtocolHandlerCustomizer<?>> 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 })//如果系統中存在Jetty相關類，引入Jetty內嵌servlet容器
   @ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
   static class EmbeddedJetty {

   2.springBoot啓動時通過SpringApplication.run方法，最終調用onRefresh()方法,取得TomcatServletWebServerFactory，啓動容器

   @Override
   protected void onRefresh() {
   	super.onRefresh();
   	try {
   		createWebServer();//創建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的實現類正是：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);
   }