深入讲解spring boot中servlet的启动过程与原理

2023-09-10 21:18:04 65

前言

本文主要介绍了关于springboot中servlet启动过程与原理的相关内容，下面话不多说了，来一起看看详细的介绍吧

启动过程与原理：

1springboot应用启动运行run方法

StopWatchstopWatch=newStopWatch();
stopWatch.start();
ConfigurableApplicationContextcontext=null;
FailureAnalyzersanalyzers=null;
configureHeadlessProperty();
SpringApplicationRunListenerslisteners=getRunListeners(args);
listeners.starting();
try{
ApplicationArgumentsapplicationArguments=newDefaultApplicationArguments(
args);
ConfigurableEnvironmentenvironment=prepareEnvironment(listeners,
applicationArguments);
BannerprintedBanner=printBanner(environment);
//创建一个ApplicationContext容器
context=createApplicationContext();
analyzers=newFailureAnalyzers(context);
prepareContext(context,environment,listeners,applicationArguments,
printedBanner);
//刷新IOC容器
refreshContext(context);
afterRefresh(context,applicationArguments);
listeners.finished(context,null);
stopWatch.stop();
if(this.logStartupInfo){
newStartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(),stopWatch);
}
returncontext;
}
catch(Throwableex){
handleRunFailure(context,listeners,analyzers,ex);
thrownewIllegalStateException(ex);
}

2 createApplicationContext():创建IOC容器,如果是web应用则创建AnnotationConfigEmbeddedWebApplacation的IOC容器,如果不是,则创建AnnotationConfigApplication的IOC容器

publicstaticfinalStringDEFAULT_CONTEXT_CLASS="org.springframework.context."
+"annotation.AnnotationConfigApplicationContext";

/**
*Theclassnameofapplicationcontextthatwillbeusedbydefaultforweb
*environments.
*/
publicstaticfinalStringDEFAULT_WEB_CONTEXT_CLASS="org.springframework."
+"boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext";


protectedConfigurableApplicationContextcreateApplicationContext(){
ClasscontextClass=this.applicationContextClass;
if(contextClass==null){
try{
//根据应用环境,创建不同的IOC容器
contextClass=Class.forName(this.webEnvironment
?DEFAULT_WEB_CONTEXT_CLASS:DEFAULT_CONTEXT_CLASS);
}
catch(ClassNotFoundExceptionex){
thrownewIllegalStateException(
"UnablecreateadefaultApplicationContext,"
+"pleasespecifyanApplicationContextClass",
ex);
}
}
return(ConfigurableApplicationContext)BeanUtils.instantiate(contextClass);
}

3 refreshContext(context)springboot刷新IOC容器(创建容器对象,并初始化容器,创建容器每一个组件)

privatevoidrefreshContext(ConfigurableApplicationContextcontext){
refresh(context);
if(this.registerShutdownHook){
try{
context.registerShutdownHook();
}
catch(AccessControlExceptionex){
//Notallowedinsomeenvironments.
}
}
}

4refresh(context);刷新刚才创建的IOC容器

protectedvoidrefresh(ApplicationContextapplicationContext){
Assert.isInstanceOf(AbstractApplicationContext.class,applicationContext);
((AbstractApplicationContext)applicationContext).refresh();
}

5调用父类的refresh()的方法

publicvoidrefresh()throwsBeansException,IllegalStateException{
Objectvar1=this.startupShutdownMonitor;
synchronized(this.startupShutdownMonitor){
this.prepareRefresh();
ConfigurableListableBeanFactorybeanFactory=this.obtainFreshBeanFactory();
this.prepareBeanFactory(beanFactory);

try{
this.postProcessBeanFactory(beanFactory);
this.invokeBeanFactoryPostProcessors(beanFactory);
this.registerBeanPostProcessors(beanFactory);
this.initMessageSource();
this.initApplicationEventMulticaster();
this.onRefresh();
this.registerListeners();
this.finishBeanFactoryInitialization(beanFactory);
this.finishRefresh();
}catch(BeansExceptionvar9){
if(this.logger.isWarnEnabled()){
this.logger.warn("Exceptionencounteredduringcontextinitialization-cancellingrefreshattempt:"+var9);
}

this.destroyBeans();
this.cancelRefresh(var9);
throwvar9;
}finally{
this.resetCommonCaches();
}

}
}

6 抽象父类AbstractApplicationContext类的子类EmbeddedWebApplicationContext的onRefresh方法

@Override
protectedvoidonRefresh(){
super.onRefresh();
try{
createEmbeddedServletContainer();
}
catch(Throwableex){
thrownewApplicationContextException("Unabletostartembeddedcontainer",
ex);
}
}

7 在createEmbeddedServletContainer放啊发中会获取嵌入式Servlet容器工厂,由容器工厂创建Servlet

privatevoidcreateEmbeddedServletContainer(){
EmbeddedServletContainerlocalContainer=this.embeddedServletContainer;
ServletContextlocalServletContext=getServletContext();
if(localContainer==null&&localServletContext==null){
//获取嵌入式Servlet容器工厂
EmbeddedServletContainerFactorycontainerFactory=getEmbeddedServletContainerFactory();
//根据容器工厂获取对应嵌入式Servlet容器
this.embeddedServletContainer=containerFactory
.getEmbeddedServletContainer(getSelfInitializer());
}
elseif(localServletContext!=null){
try{
getSelfInitializer().onStartup(localServletContext);
}
catch(ServletExceptionex){
thrownewApplicationContextException("Cannotinitializeservletcontext",
ex);
}
}
initPropertySources();
}

8 从IOC容器中获取Servlet容器工厂

//EmbeddedWebApplicationContext#getEmbeddedServletContainerFactory
protectedEmbeddedServletContainerFactorygetEmbeddedServletContainerFactory(){
//Usebeannamessothatwedon'tconsiderthehierarchy
String[]beanNames=getBeanFactory()
.getBeanNamesForType(EmbeddedServletContainerFactory.class);
if(beanNames.length==0){
thrownewApplicationContextException(
"UnabletostartEmbeddedWebApplicationContextduetomissing"
+"EmbeddedServletContainerFactorybean.");
}
if(beanNames.length>1){
thrownewApplicationContextException(
"UnabletostartEmbeddedWebApplicationContextduetomultiple"
+"EmbeddedServletContainerFactorybeans:"
+StringUtils.arrayToCommaDelimitedString(beanNames));
}
returngetBeanFactory().getBean(beanNames[0],
EmbeddedServletContainerFactory.class);
}

9 使用Servlet容器工厂获取嵌入式Servlet容器,具体使用哪一个容器工厂看配置环境依赖

this.embeddedServletContainer=containerFactory
.getEmbeddedServletContainer(getSelfInitializer());

10 上述创建过程首先启动IOC容器,接着启动嵌入式Servlet容器,接着将IOC容器中剩下没有创建的对象获取出来,比如自己创建的controller

//Instantiateallremaining(non-lazy-init)singletons.
finishBeanFactoryInitialization(beanFactory);

protectedvoidfinishBeanFactoryInitialization(ConfigurableListableBeanFactorybeanFactory){
//Initializeconversionserviceforthiscontext.
if(beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME)&&
beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME,ConversionService.class)){
beanFactory.setConversionService(
beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME,ConversionService.class));
}

//Registeradefaultembeddedvalueresolverifnobeanpost-processor
//(suchasaPropertyPlaceholderConfigurerbean)registeredanybefore:
//atthispoint,primarilyforresolutioninannotationattributevalues.
if(!beanFactory.hasEmbeddedValueResolver()){
beanFactory.addEmbeddedValueResolver(newStringValueResolver(){
@Override
publicStringresolveStringValue(StringstrVal){
returngetEnvironment().resolvePlaceholders(strVal);
}
});
}

//InitializeLoadTimeWeaverAwarebeansearlytoallowforregisteringtheirtransformersearly.
String[]weaverAwareNames=beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class,false,false);
for(StringweaverAwareName:weaverAwareNames){
getBean(weaverAwareName);
}

//StopusingthetemporaryClassLoaderfortypematching.
beanFactory.setTempClassLoader(null);

//Allowforcachingallbeandefinitionmetadata,notexpectingfurtherchanges.
beanFactory.freezeConfiguration();

//Instantiateallremaining(non-lazy-init)singletons.
beanFactory.preInstantiateSingletons();
}

看看preInstantiateSingletons方法

publicvoidpreInstantiateSingletons()throwsBeansException{
if(this.logger.isDebugEnabled()){
this.logger.debug("Pre-instantiatingsingletonsin"+this);
}

ListbeanNames=newArrayList(this.beanDefinitionNames);
Iteratorvar2=beanNames.iterator();

while(true){
while(true){
StringbeanName;
RootBeanDefinitionbd;
do{
do{
do{
if(!var2.hasNext()){
var2=beanNames.iterator();

while(var2.hasNext()){
beanName=(String)var2.next();
ObjectsingletonInstance=this.getSingleton(beanName);
if(singletonInstanceinstanceofSmartInitializingSingleton){
finalSmartInitializingSingletonsmartSingleton=(SmartInitializingSingleton)singletonInstance;
if(System.getSecurityManager()!=null){
AccessController.doPrivileged(newPrivilegedAction

深入讲解spring boot中servlet的启动过程与原理

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