SpringBoot如何实现Tomcat自动配置

2023-07-04 08:18:02 188

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

@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})
publicclassServletWebServerFactoryAutoConfiguration{

	@Bean
	publicServletWebServerFactoryCustomizerservletWebServerFactoryCustomizer(
			ServerPropertiesserverProperties){
		returnnewServletWebServerFactoryCustomizer(serverProperties);
	}

	@Bean
	@ConditionalOnClass(name="org.apache.catalina.startup.Tomcat")
	publicTomcatServletWebServerFactoryCustomizertomcatServletWebServerFactoryCustomizer(
			ServerPropertiesserverProperties){
		returnnewTomcatServletWebServerFactoryCustomizer(serverProperties);
	}

	/**
	*Registersa{@linkWebServerFactoryCustomizerBeanPostProcessor}.Registeredvia
	*{@linkImportBeanDefinitionRegistrar}forearlyregistration.
	*/
	publicstaticclassBeanPostProcessorsRegistrar
			implementsImportBeanDefinitionRegistrar,BeanFactoryAware{

		privateConfigurableListableBeanFactorybeanFactory;

		@Override
		publicvoidsetBeanFactory(BeanFactorybeanFactory)throwsBeansException{
			if(beanFactoryinstanceofConfigurableListableBeanFactory){
				this.beanFactory=(ConfigurableListableBeanFactory)beanFactory;
			}
		}

		@Override
		publicvoidregisterBeanDefinitions(AnnotationMetadataimportingClassMetadata,
				BeanDefinitionRegistryregistry){
			if(this.beanFactory==null){
				return;
			}
			registerSyntheticBeanIfMissing(registry,
					"webServerFactoryCustomizerBeanPostProcessor",
					WebServerFactoryCustomizerBeanPostProcessor.class);
			registerSyntheticBeanIfMissing(registry,
					"errorPageRegistrarBeanPostProcessor",
					ErrorPageRegistrarBeanPostProcessor.class);
		}

		privatevoidregisterSyntheticBeanIfMissing(BeanDefinitionRegistryregistry,
				Stringname,ClassbeanClass){
			if(ObjectUtils.isEmpty(
					this.beanFactory.getBeanNamesForType(beanClass,true,false))){
				RootBeanDefinitionbeanDefinition=newRootBeanDefinition(beanClass);
				beanDefinition.setSynthetic(true);
				registry.registerBeanDefinition(name,beanDefinition);
			}
		}

	}

}

首先看一下上方的几个注解

@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
@ConditionalOnXXX在之前的文章中已经无数次提到了，就不再阐述了
@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

@ConfigurationProperties(prefix="server",ignoreUnknownFields=true)
publicclassServerProperties{

	privateIntegerport;

	privateInetAddressaddress;

	@NestedConfigurationProperty
	privatefinalErrorPropertieserror=newErrorProperties();

	privateBooleanuseForwardHeaders;

	privateStringserverHeader;

	privateintmaxHttpHeaderSize=0;//bytes

	privateDurationconnectionTimeout;

	@NestedConfigurationProperty
	privateSslssl;

	@NestedConfigurationProperty
	privatefinalCompressioncompression=newCompression();

	@NestedConfigurationProperty
	privatefinalHttp2http2=newHttp2();

	privatefinalServletservlet=newServlet();

	privatefinalTomcattomcat=newTomcat();

	privatefinalJettyjetty=newJetty();

	privatefinalUndertowundertow=newUndertow();
}

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

@Import
BeanPostProcessorsRegistrar
publicstaticclassBeanPostProcessorsRegistrar
			implementsImportBeanDefinitionRegistrar,BeanFactoryAware{
		@Override
		publicvoidregisterBeanDefinitions(AnnotationMetadataimportingClassMetadata,
				BeanDefinitionRegistryregistry){
			if(this.beanFactory==null){
				return;
			}
			registerSyntheticBeanIfMissing(registry,
					"webServerFactoryCustomizerBeanPostProcessor",
					WebServerFactoryCustomizerBeanPostProcessor.class);
			registerSyntheticBeanIfMissing(registry,
					"errorPageRegistrarBeanPostProcessor",
					ErrorPageRegistrarBeanPostProcessor.class);
		}

		privatevoidregisterSyntheticBeanIfMissing(BeanDefinitionRegistryregistry,
				Stringname,ClassbeanClass){
			if(ObjectUtils.isEmpty(
					this.beanFactory.getBeanNamesForType(beanClass,true,false))){
				RootBeanDefinitionbeanDefinition=newRootBeanDefinition(beanClass);
				beanDefinition.setSynthetic(true);
				registry.registerBeanDefinition(name,beanDefinition);
			}
		}

	}

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

EmbeddedTomcat

@Configuration
@ConditionalOnClass({Servlet.class,Tomcat.class,UpgradeProtocol.class})
@ConditionalOnMissingBean(value=ServletWebServerFactory.class,search=SearchStrategy.CURRENT)
publicstaticclassEmbeddedTomcat{

@Bean
publicTomcatServletWebServerFactorytomcatServletWebServerFactory(){
returnnewTomcatServletWebServerFactory();
}

}

这个类会在存在Tomcat相关jar包时添加一个TomcatServletWebServerFactorybean

其他两个相信大家都知道怎么回事了

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

protectedvoidonRefresh(){
	super.onRefresh();
try{
	createWebServer();
}
	catch(Throwableex){
		thrownewApplicationContextException("Unabletostartwebserver",ex);
	}
}

Tomcat的启动就在createWebServer方法里面了

privatevoidcreateWebServer(){
WebServerwebServer=this.webServer;
ServletContextservletContext=getServletContext();
//第一次访问的时候两个对象都为空
if(webServer==null&&servletContext==null){
ServletWebServerFactoryfactory=getWebServerFactory();
this.webServer=factory.getWebServer(getSelfInitializer());
}
elseif(servletContext!=null){
try{
getSelfInitializer().onStartup(servletContext);
}
catch(ServletExceptionex){
thrownewApplicationContextException("Cannotinitializeservletcontext",
ex);
}
}
initPropertySources();
}

首先看一下getWebServerFactory

protectedServletWebServerFactorygetWebServerFactory(){
//这里获取的beanname就是上方注册的tomcatServletWebServerFactory了
String[]beanNames=getBeanFactory()
.getBeanNamesForType(ServletWebServerFactory.class);
if(beanNames.length==0){
thrownewApplicationContextException(
"UnabletostartServletWebServerApplicationContextduetomissing"
+"ServletWebServerFactorybean.");
}
if(beanNames.length>1){
thrownewApplicationContextException(
"UnabletostartServletWebServerApplicationContextduetomultiple"
+"ServletWebServerFactorybeans:"
+StringUtils.arrayToCommaDelimitedString(beanNames));
}
returngetBeanFactory().getBean(beanNames[0],ServletWebServerFactory.class);
}

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beantomcatServletWebServerFactory的时候就会执行后置处理器的postProcessBeforeInitialization方法

publicObjectpostProcessBeforeInitialization(Objectbean,StringbeanName)
			throwsBeansException{
	if(beaninstanceofWebServerFactory){
		postProcessBeforeInitialization((WebServerFactory)bean);
	}
	returnbean;
}
privatevoidpostProcessBeforeInitialization(WebServerFactorywebServerFactory){
LambdaSafe
.callbacks(WebServerFactoryCustomizer.class,getCustomizers(),
webServerFactory)
.withLogger(WebServerFactoryCustomizerBeanPostProcessor.class)
.invoke((customizer)->customizer.customize(webServerFactory));
}

privateCollection>getCustomizers(){
if(this.customizers==null){
//Lookupdoesnotincludetheparentcontext
this.customizers=newArrayList<>(getWebServerFactoryCustomizerBeans());
this.customizers.sort(AnnotationAwareOrderComparator.INSTANCE);
this.customizers=Collections.unmodifiableList(this.customizers);
}
returnthis.customizers;
}

@SuppressWarnings({"unchecked","rawtypes"})
privateCollection>getWebServerFactoryCustomizerBeans(){
return(Collection)this.beanFactory
.getBeansOfType(WebServerFactoryCustomizer.class,false,false).values();
}

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

publicWebServergetWebServer(ServletContextInitializer...initializers){
Tomcattomcat=newTomcat();
FilebaseDir=(this.baseDirectory!=null?this.baseDirectory
:createTempDir("tomcat"));
tomcat.setBaseDir(baseDir.getAbsolutePath());
Connectorconnector=newConnector(this.protocol);
tomcat.getService().addConnector(connector);
customizeConnector(connector);
tomcat.setConnector(connector);
tomcat.getHost().setAutoDeploy(false);
configureEngine(tomcat.getEngine());
for(ConnectoradditionalConnector:this.additionalTomcatConnectors){
tomcat.getService().addConnector(additionalConnector);
}
prepareContext(tomcat.getHost(),initializers);
returngetTomcatWebServer(tomcat);
}
protectedTomcatWebServergetTomcatWebServer(Tomcattomcat){
returnnewTomcatWebServer(tomcat,getPort()>=0);
}
publicTomcatWebServer(Tomcattomcat,booleanautoStart){
Assert.notNull(tomcat,"TomcatServermustnotbenull");
this.tomcat=tomcat;
this.autoStart=autoStart;
initialize();
}
privatevoidinitialize()throwsWebServerException{
TomcatWebServer.logger.info("Tomcatinitializedwithport(s):"+getPortsDescription(false));
synchronized(this.monitor){
try{
addInstanceIdToEngineName();

Contextcontext=findContext();
context.addLifecycleListener((event)->{
if(context.equals(event.getSource())
&&Lifecycle.START_EVENT.equals(event.getType())){
//Removeserviceconnectorssothatprotocolbindingdoesn't
//happenwhentheserviceisstarted.
removeServiceConnectors();
}
});

//Starttheservertotriggerinitializationlisteners
this.tomcat.start();

//Wecanre-throwfailureexceptiondirectlyinthemainthread
rethrowDeferredStartupExceptions();

try{
ContextBindings.bindClassLoader(context,context.getNamingToken(),
getClass().getClassLoader());
}
catch(NamingExceptionex){
//Namingisnotenabled.Continue
}

//UnlikeJetty,allTomcatthreadsaredaemonthreads.Wecreatea
//blockingnon-daemontostopimmediateshutdown
startDaemonAwaitThread();
}
catch(Exceptionex){
thrownewWebServerException("UnabletostartembeddedTomcat",ex);
}
}
}

以上就是SpringBoot如何实现Tomcat自动配置的详细内容，更多关于SpringBoot实现Tomcat自动配置的资料请关注毛票票其它相关文章！

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SpringBoot如何实现Tomcat自动配置

准备工作

启动

接着往下看

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