springboot 基于Tomcat容器的自启动流程分析

2023-07-31 18:26:03 303

Springboot内置了Tomcat的容器，我们今天来说一下Springboot的自启动流程。

一、Spring通过注解导入Bean大体可分为四种方式，我们主要来说以下Import的两种实现方法：

1、通过实现ImportSerlector接口，实现Bean加载：

publicclassTestServiceImpl{
publicvoidtestImpl(){
System.out.println("我是通过importSelector导入进来的service");
}
}
publicclassTestServiceimplementsImportSelector{
@Override
publicString[]selectImports(AnnotationMetadataannotationMetadata){
returnnewString[]{"com.ycdhz.service.TestServiceImpl"};
}
}
@Configuration
@Import(value={TestService.class})
publicclassTestConfig{
}
publicclassTestController{
@Autowired
privateTestServiceImpltestServiceImpl;

@RequestMapping("testImpl")
publicStringtestTuling(){
testServiceImpl.testImpl();
return"Ok";
}
}

2、通过实现ImportSerlector接口，实现Bean加载：

publicclassTestService{
publicTestService(){
System.out.println("我是通过ImportBeanDefinitionRegistrar导入进来的组件");
}
}
publicclassTestImportBeanDefinitionRegistrarimplementsImportBeanDefinitionRegistrar{
@Override
publicvoidregisterBeanDefinitions(AnnotationMetadataimportingClassMetadata,BeanDefinitionRegistryregistry){
//定义一个BeanDefinition
RootBeanDefinitionbeanDefinition=newRootBeanDefinition(TestService.class);
//把自定义的bean定义导入到容器中
registry.registerBeanDefinition("testService",beanDefinition);
}
}
@Configuration
@Import(TestImportBeanDefinitionRegistrar.class)
publicclassTestConfig{
}

二、Springboot启动过程中会自动装配

我们从spring-boot-autoconfigure-2.0.6.RELEASE.jar下搜索到Tomcat的相关配置，发现有两个自动装配类，分别包含了三个定制器（面向对象的单一职责原则），还有一个工厂类。

2.1、TomcatWebServerFactoryCustomizer：定制Servlet和Reactive服务器通用的Tomcat特定功能。

publicclassTomcatWebServerFactoryCustomizerimplements
WebServerFactoryCustomizer,Ordered{
@Override
publicvoidcustomize(ConfigurableTomcatWebServerFactoryfactory){
ServerPropertiesproperties=this.serverProperties;
ServerProperties.TomcattomcatProperties=properties.getTomcat();
PropertyMapperpropertyMapper=PropertyMapper.get();
propertyMapper.from(tomcatProperties::getBasedir).whenNonNull()
.to(factory::setBaseDirectory);
propertyMapper.from(tomcatProperties::getBackgroundProcessorDelay).whenNonNull()
.as(Duration::getSeconds).as(Long::intValue)
.to(factory::setBackgroundProcessorDelay);
customizeRemoteIpValve(factory);
propertyMapper.from(tomcatProperties::getMaxThreads).when(this::isPositive)
.to((maxThreads)->customizeMaxThreads(factory,
tomcatProperties.getMaxThreads()));
propertyMapper.from(tomcatProperties::getMinSpareThreads).when(this::isPositive)
.to((minSpareThreads)->customizeMinThreads(factory,minSpareThreads));
propertyMapper.from(()->determineMaxHttpHeaderSize()).when(this::isPositive)
.to((maxHttpHeaderSize)->customizeMaxHttpHeaderSize(factory,
maxHttpHeaderSize));
propertyMapper.from(tomcatProperties::getMaxHttpPostSize)
.when((maxHttpPostSize)->maxHttpPostSize!=0)
.to((maxHttpPostSize)->customizeMaxHttpPostSize(factory,
maxHttpPostSize));
propertyMapper.from(tomcatProperties::getAccesslog)
.when(ServerProperties.Tomcat.Accesslog::isEnabled)
.to((enabled)->customizeAccessLog(factory));
propertyMapper.from(tomcatProperties::getUriEncoding).whenNonNull()
.to(factory::setUriEncoding);
propertyMapper.from(properties::getConnectionTimeout).whenNonNull()
.to((connectionTimeout)->customizeConnectionTimeout(factory,
connectionTimeout));
propertyMapper.from(tomcatProperties::getMaxConnections).when(this::isPositive)
.to((maxConnections)->customizeMaxConnections(factory,maxConnections));
propertyMapper.from(tomcatProperties::getAcceptCount).when(this::isPositive)
.to((acceptCount)->customizeAcceptCount(factory,acceptCount));
customizeStaticResources(factory);
customizeErrorReportValve(properties.getError(),factory);
}
}

2.2、ServletWebServerFactoryCustomizer：WebServerFactoryCustomizer将ServerProperties属性应用于Tomcatweb服务器。

publicclassServletWebServerFactoryCustomizerimplements
WebServerFactoryCustomizer,Ordered{
privatefinalServerPropertiesserverProperties;
publicServletWebServerFactoryCustomizer(ServerPropertiesserverProperties){
this.serverProperties=serverProperties;
}
@Override
publicintgetOrder(){
return0;
}
@Override
publicvoidcustomize(ConfigurableServletWebServerFactoryfactory){
PropertyMappermap=PropertyMapper.get().alwaysApplyingWhenNonNull();
map.from(this.serverProperties::getPort).to(factory::setPort);
map.from(this.serverProperties::getAddress).to(factory::setAddress);
map.from(this.serverProperties.getServlet()::getContextPath)
.to(factory::setContextPath);
map.from(this.serverProperties.getServlet()::getApplicationDisplayName)
.to(factory::setDisplayName);
map.from(this.serverProperties.getServlet()::getSession).to(factory::setSession);
map.from(this.serverProperties::getSsl).to(factory::setSsl);
map.from(this.serverProperties.getServlet()::getJsp).to(factory::setJsp);
map.from(this.serverProperties::getCompression).to(factory::setCompression);
map.from(this.serverProperties::getHttp2).to(factory::setHttp2);
map.from(this.serverProperties::getServerHeader).to(factory::setServerHeader);
map.from(this.serverProperties.getServlet()::getContextParameters)
.to(factory::setInitParameters);
}
}

2.3、ServletWebServerFactoryCustomizer：WebServerFactoryCustomizer将ServerProperties属性应用于Tomcatweb服务器。

publicclassTomcatServletWebServerFactoryCustomizer
implementsWebServerFactoryCustomizer,Ordered{
privatefinalServerPropertiesserverProperties;
publicTomcatServletWebServerFactoryCustomizer(ServerPropertiesserverProperties){
this.serverProperties=serverProperties;
}
@Override
publicvoidcustomize(TomcatServletWebServerFactoryfactory){
ServerProperties.TomcattomcatProperties=this.serverProperties.getTomcat();
if(!ObjectUtils.isEmpty(tomcatProperties.getAdditionalTldSkipPatterns())){
factory.getTldSkipPatterns()
.addAll(tomcatProperties.getAdditionalTldSkipPatterns());
}
if(tomcatProperties.getRedirectContextRoot()!=null){
customizeRedirectContextRoot(factory,
tomcatProperties.getRedirectContextRoot());
}
if(tomcatProperties.getUseRelativeRedirects()!=null){
customizeUseRelativeRedirects(factory,
tomcatProperties.getUseRelativeRedirects());
}
}
}

三、有了TomcatServletWebServerFactory，相当于有了Spring加载的入口

通过AbstractApplicationContext#onReFresh()在IOC容器中的带动tomcat启动，然后在接着执行ioc容器的其他步骤。

我们通过断点可以观察Tomcat加载的整个生命周期，以及三个定制器的加载过程。

@Override
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);
//设置是否自动启动
tomcat.getHost().setAutoDeploy(false);
//创建Tomcat引擎
configureEngine(tomcat.getEngine());
for(ConnectoradditionalConnector:this.additionalTomcatConnectors){
tomcat.getService().addConnector(additionalConnector);
}
//刷新上下文
prepareContext(tomcat.getHost(),initializers);
//准备启动
returngetTomcatWebServer(tomcat);
}

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){
stopSilently();
thrownewWebServerException("UnabletostartembeddedTomcat",ex);
}
}
}

备注：在这个过程中我们需要了解Bean的生命周期，Tomcat的三个定制器均在BeanPostProcessorsRegistrar（Bean后置处理器）过程中加载；

构造方法-->Bean后置处理器Before-->InitializingBean-->init-method-->Bean后置处理器After

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#doCreateBean
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#initializeBean

protectedObjectdoCreateBean(finalStringbeanName,finalRootBeanDefinitionmbd,final@NullableObject[]args)
throwsBeanCreationException{
//Instantiatethebean.
BeanWrapperinstanceWrapper=null;
if(mbd.isSingleton()){
instanceWrapper=this.factoryBeanInstanceCache.remove(beanName);
}
if(instanceWrapper==null){
//构造方法
instanceWrapper=createBeanInstance(beanName,mbd,args);
}
finalObjectbean=instanceWrapper.getWrappedInstance();
ClassbeanType=instanceWrapper.getWrappedClass();
if(beanType!=NullBean.class){
mbd.resolvedTargetType=beanType;
}
//Initializethebeaninstance.
......
returnexposedObject;
}
protectedObjectinitializeBean(finalStringbeanName,finalObjectbean,@NullableRootBeanDefinitionmbd){
if(System.getSecurityManager()!=null){
AccessController.doPrivileged((PrivilegedAction

springboot 基于Tomcat容器的自启动流程分析

一、Spring通过注解导入Bean大体可分为四种方式，我们主要来说以下Import的两种实现方法：

二、Springboot启动过程中会自动装配

三、有了TomcatServletWebServerFactory，相当于有了Spring加载的入口

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