SpringBoot嵌入式Tomcat的自动配置原理

落日映苍穹つ 2023-08-17 15:28 114阅读 0赞

> 在读本篇文章之前如果你读过这篇文章[SpringBoot自动装配原理解析][SpringBoot]应该会更加轻松

##### 准备工作 #####

我们知道SpringBoot的自动装配的秘密在`org.springframework.boot.autoconfigure`包下的`spring.factories`文件中，而嵌入Tomcat的原理就在这个文件中加载的一个配置类：`org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration`

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 <td><pre>1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 </pre></td> 
 <td><pre>@Configuration @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE) @ConditionalOnClass(ServletRequest.class) @ConditionalOnWebApplication(type = Type.SERVLET) @EnableConfigurationProperties(ServerProperties.class) @Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class, 		ServletWebServerFactoryConfiguration.EmbeddedTomcat.class, 		ServletWebServerFactoryConfiguration.EmbeddedJetty.class, 		ServletWebServerFactoryConfiguration.EmbeddedUndertow.class }) public class ServletWebServerFactoryAutoConfiguration {
 	@Bean 	public ServletWebServerFactoryCustomizer servletWebServerFactoryCustomizer( ServerProperties serverProperties) {
 		return new ServletWebServerFactoryCustomizer(serverProperties); 	} 	@Bean 	@ConditionalOnClass(name = "org.apache.catalina.startup.Tomcat") 	public TomcatServletWebServerFactoryCustomizer tomcatServletWebServerFactoryCustomizer( ServerProperties serverProperties) {
 		return new TomcatServletWebServerFactoryCustomizer(serverProperties); 	} 	/** * Registers a { @link WebServerFactoryCustomizerBeanPostProcessor}. Registered via * { @link ImportBeanDefinitionRegistrar} for early registration. */ 	public static class BeanPostProcessorsRegistrar implements ImportBeanDefinitionRegistrar, BeanFactoryAware {
 		private ConfigurableListableBeanFactory beanFactory; 		@Override 		public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
 			if (beanFactory instanceof ConfigurableListableBeanFactory) {
 				this.beanFactory = (ConfigurableListableBeanFactory) beanFactory; 			} 		} 		@Override 		public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
 			if (this.beanFactory == null) {
 				return; 			} 			registerSyntheticBeanIfMissing(registry, 					"webServerFactoryCustomizerBeanPostProcessor", 					WebServerFactoryCustomizerBeanPostProcessor.class); 			registerSyntheticBeanIfMissing(registry, 					"errorPageRegistrarBeanPostProcessor", 					ErrorPageRegistrarBeanPostProcessor.class); 		} 		private void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry, String name, Class&lt;?&gt; beanClass) {
 			if (ObjectUtils.isEmpty( 					this.beanFactory.getBeanNamesForType(beanClass, true, false))) {
 				RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass); 				beanDefinition.setSynthetic(true); 				registry.registerBeanDefinition(name, beanDefinition); 			} 		} 	} } </pre></td> 
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首先看一下上方的几个注解

1.  `@AutoConfigureOrder`这个注解是决定配置类的加载顺序的，当注解里的值越小越先加载，而`Ordered.HIGHEST_PRECEDENCE`的值是`Integer.MIN_VALUE`也就是说这个类肯定是最先加载的那一批
2.  `@ConditionalOnXXX`在之前的文章中已经无数次提到了，就不再阐述了
3.  `@EnableConfigurationProperties`开启`ServerProperties`类的属性值配置。而这个类里面包含的就是Web服务的配置

这个类的代码太多了，这里就不一一贴出来了，我们平常在`application.properties`中配置的server.xxx就是这个类中属性

1.  `@Import`引入了4个类，看都是什么吧
2.  `BeanPostProcessorsRegistrar`

这个类注册了两个bean：`WebServerFactoryCustomizerBeanPostProcessor`和`ErrorPageRegistrarBeanPostProcessor`关于这两个bean的作用稍后再详细介绍

1.  `EmbeddedTomcat`

这个类会在存在Tomcat相关jar包时添加一个`TomcatServletWebServerFactory`bean

其他两个相信大家都知道怎么回事了

1.  除了这些这个类还注入了两个类`ServletWebServerFactoryCustomizer`和`TomcatServletWebServerFactoryCustomizer`

现在前期准备工作已经做好了，看一下这个Tomcat是如何启动的吧

##### 启动 #####

启动入口在`ServletWebServerApplicationContext`中的`onRefresh`方法

Tomcat的启动就在`createWebServer`方法里面了

首先看一下`getWebServerFactory`

准备环境里注册的bean现在出来一个了。注意，上方还注册了一个后置处理器`EmbeddedServletContainerCustomizerBeanPostProcessor`，获取bean`tomcatServletWebServerFactory`的时候就会执行后置处理器的`postProcessBeforeInitialization`方法

这个处理器的作用是获得所有定制器，然后执行定制器的方法

###### 接着往下看 ######

这个时候就可以启动Tomcat了

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 <td><pre>public WebServer getWebServer(ServletContextInitializer... initializers) {
 		Tomcat tomcat = new Tomcat(); 		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); 		return getTomcatWebServer(tomcat); 	} protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
 		return new TomcatWebServer(tomcat, getPort() &gt;= 0); 	} public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
 		Assert.notNull(tomcat, "Tomcat Server must not be null"); 		this.tomcat = tomcat; 		this.autoStart = autoStart; 		initialize(); 	} private void initialize() throws WebServerException {
 		TomcatWebServer.logger 				.info("Tomcat initialized with port(s): " + getPortsDescription(false)); 		synchronized (this.monitor) {
 			try {
 				addInstanceIdToEngineName(); 				Context context = findContext(); 				context.addLifecycleListener((event) -&gt; {
 					if (context.equals(event.getSource()) 							&amp;&amp; Lifecycle.START_EVENT.equals(event.getType())) {
 						// Remove service connectors so that protocol binding doesn't 						// happen when the service is started. 						removeServiceConnectors(); 					} 				}); 				// Start the server to trigger initialization listeners 				this.tomcat.start(); 				// We can re-throw failure exception directly in the main thread 				rethrowDeferredStartupExceptions(); 				try {
 					ContextBindings.bindClassLoader(context, context.getNamingToken(), 							getClass().getClassLoader()); 				} 				catch (NamingException ex) {
 					// Naming is not enabled. Continue 				} 				// Unlike Jetty, all Tomcat threads are daemon threads. We create a 				// blocking non-daemon to stop immediate shutdown 				startDaemonAwaitThread(); 			} 			catch (Exception ex) {
 				throw new WebServerException("Unable to start embedded Tomcat", ex); 			} 		} 	}</pre></td> 
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