SpringBoot内置tomcat启动原理详解

SpringBoot内置tomcat启动原理详解

前言

不得不说SpringBoot的开发者是在为大众程序猿谋福利，把大家都惯成了懒汉，xml不配置了，连tomcat也懒的配置了，典型的一键启动系统，那么tomcat在springboot是怎么启动的呢？

内置tomcat

开发阶段对我们来说使用内置的tomcat是非常够用了，当然也可以使用jetty。

org.springframework.boot

spring-boot-starter-web

2.1.6.RELEASE

@SpringBootApplication

public class MySpringbootTomcatStarter{

public static void main(String[] args) {

Long time=System.currentTimeMillis();

SpringApplication.run(MySpringbootTomcatStarter.class);

System.out.println("===应用启动耗时："+(System.currentTimeMillis()-time)+"===");

}

}

这里是main函数入口，两句代码最耀眼，分别是SpringBootApplication注解和SpringApplication.run()方法。

发布生产

发布的时候，目前大多数的做法还是排除内置的tomcat，打瓦包（war）然后部署在生产的tomcat中，好吧，那打包的时候应该怎么处理？

org.springframework.boot

spring-boot-starter-web

org.springframework.boot

spring-boot-starter-tomcat

javax.servlet

javax.servlet-api

3.1.0

provided

更新main函数，主要是继承SpringBootServletInitializer，并重写configure()方法。

@SpringBootApplication

public class MySpringbootTomcatStarter extends SpringBootServletInitializer {

public static void main(String[] args) {

Long time=System.currentTimeMillis();

SpringApplication.run(MySpringbootTomcatStarter.class);

System.out.println("===应用启动耗时："+(System.currentTimeMillis()-time)+"===");

}

@Override

protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {

return builder.sources(this.getClass());

}

}

从main函数说起

public static ConfigurableApplicationContext run(Class> primarySource, String... args) {

return run(new Class[]{primarySource}, args);

}

--这里run方法返回的是ConfigurableApplicationContext

public static ConfigurableApplicationContext run(Class>[] primarySources, String[] args) {

return (new SpringApplication(primarySources)).run(args);

}

public ConfigurableApplicationContext run(String... args) {

ConfigurableApplicationContext context = null;

Collection exceptionReporters = new ArrayList();

this.configureHeadlessProperty();

SpringApplicationRunListeners listeners = this.getRunListeners(args);

listeners.starting();

Collection exceptionReporters;

try {

ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);

ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);

this.configureIgnoreBeanInfo(environment);

//打印banner，这里你可以自己涂鸦一下，换成自己项目的logo

Banner printedBanner = this.printBanner(environment);

//创建应用上下文

context = this.createApplicationContext();

exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);

//预处理上下文

this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);

//刷新上下文

this.refreshContext(context);

//再刷新上下文

this.afterRefresh(context, applicationArguments);

listeners.started(context);

this.callRunners(context, applicationArguments);

} catch (Throwable var10) {

}

try {

listeners.running(context);

return context;

} catch (Throwable var9) {

}

}

既然我们想知道tomcat在SpringBoot中是怎么启动的，那么run方法中，重点关注创建应用上下文（createApplicationContext）和刷新上下文（refreshContext）。

创建上下文

//创建上下文

protected ConfigurableApplicationContext createApplicationContext() {

Class> contextClass = this.applicationContextClass;

if (contextClass == null) {

try {

switch(this.webApplicationType) {

case SERVLET:

//创建AnnotationConfigServletWebServerApplicationContext

contextClass = Class.forName("org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext");

break;

case REACTIVE:

contextClass = Class.forName("org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext");

break;

default:

contextClass = Class.forName("org.springframework.context.annotation.AnnotationConfigApplicationContext");

}

} catch (ClassNotFoundException var3) {

throw new IllegalStateException("Unable create a default ApplicationContext, please specify an ApplicationContextClass", var3);

}

}

return (ConfigurableApplicationContext)BeanUtils.instantiateClass(contextClass);

}

这里会创建AnnotationConfigServletWebServerApplicationContext类。

而AnnotationConfigServletWebServerApplicationContext类继承了ServletWebServerApplicationContext，而这个类是最终集成了AbstractApplicationContext。

刷新上下文

//SpringApplication.java

//刷新上下文

private void refreshContext(ConfigurableApplicationContext context) {

this.refresh(context);

if (this.registerShutdownHook) {

try {

context.registerShutdownHook();

} catch (AccessControlException var3) {

}

}

}

//这里直接调用最终父类AbstractApplicationContext.refresh()方法

protected void refresh(ApplicationContext applicationContext) {

((AbstractApplicationContext)applicationContext).refresh();

}

//AbstractApplicationContext.java

public void refresh() throws BeansException, IllegalStateException {

synchronized(this.startupShutdownMonitor) {

this.prepareRefresh();

ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();

this.prepareBeanFactory(beanFactory);

try {

this.postProcessBeanFactory(beanFactory);

this.invokeBeanFactoryPostProcessors(beanFactory);

this.registerBeanPostProcessors(beanFactory);

this.initMessageSource();

this.initApplicationEventMulticaster();

//调用各个子类的onRefresh()方法，也就说这里要回到子类：ServletWebServerApplicationContext，调用该类的onRefresh()方法

this.onRefresh();

this.registerListeners();

this.finishBeanFactoryInitialization(beanFactory);

this.finishRefresh();

} catch (BeansException var9) {

this.destroyBeans();

this.cancelRefresh(var9);

throw var9;

} finally {

this.resetCommonCaches();

}

}

}

//ServletWebServerApplicationContext.java

//在这个方法里看到了熟悉的面孔，this.createWebServer，神秘的面纱就要揭开了。

protected void onRefresh() {

super.onRefresh();

try {

this.createWebServer();

} catch (Throwable var2) {

}

}

//ServletWebServerApplicationContext.java

//这里是创建webServer，但是还没有启动tomcat，这里是通过ServletWebServerFactory创建，那么接着看下ServletWebServerFactory

private void createWebServer() {

WebServer webServer = this.webServer;

ServletContext servletContext = this.getServletContext();

if (webServer == null && servletContext == null) {

ServletWebServerFactory factory = this.getWebServerFactory();

this.webServer = factory.getWebServer(new ServletContextInitializer[]{this.getSelfInitializer()});

} else if (servletContext != null) {

try {

this.getSelfInitializer().onStartup(servletContext);

} catch (ServletException var4) {

}

}

this.initPropertySources();

}

//接口

public interface ServletWebServerFactory {

WebServer getWebServer(ServletContextInitializer... initializers);

}

//实现

AbstractServletWebServerFactory

JettyServletWebServerFactory

TomcatServletWebServerFactory

UndertowServletWebServerFactory

这里ServletWebServerFactory接口有4个实现类

而其中我们常用的有两个：TomcatServletWebServerFactory和JettyServletWebServerFactory。

//TomcatServletWebServerFactory.java

//这里我们使用的tomcat，所以我们查看TomcatServletWebServerFactory。到这里总算是看到了tomcat的踪迹。

@Override

public WebServer getWebServer(ServletContextInitializer... initializers) {

Tomcat tomcat = new Tomcat();

File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");

tomcat.setBaseDir(baseDir.getAbsolutePath());

//创建Connector对象

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() >= 0);

}

//Tomcat.java

//返回Engine容器，看到这里，如果熟悉tomcat源码的话，对engine不会感到陌生。

public Engine getEngine() {

Service service = getServer().findServices()[0];

if (service.getContainer() != null) {

return service.getContainer();

}

Engine engine = new StandardEngine();

engine.setName( "Tomcat" );

engine.setDefaultHost(hostname);

engine.setRealm(createDefaultRealm());

service.setContainer(engine);

return engine;

}

//Engine是最高级别容器，Host是Engine的子容器，Context是Host的子容器，Wrapper是Context的子容器

getWebServer这个方法创建了Tomcat对象，并且做了两件重要的事情：把Connector对象添加到tomcat中，configureEngine(tomcat.getEngine());

           getWebServer方法返回的是TomcatWebServer。

//TomcatWebServer.java

//这里调用构造函数实例化TomcatWebServer

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 {

//在控制台会看到这句日志

logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));

synchronized (this.monitor) {

try {

addInstanceIdToEngineName();

Context context = findContext();

context.addLifecycleListener((event) -> {

if (context.equals(event.getSource()) && Lifecycle.START_EVENT.equals(event.getType())) {

removeServiceConnectors();

}

});

//===启动tomcat服务===

this.tomcat.start();

rethrowDeferredStartupExceptions();

try {

ContextBindings.bindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());

}

catch (NamingException ex) {

}

//开启阻塞非守护进程

startDaemonAwaitThread();

}

catch (Exception ex) {

stopSilently();

destroySilently();

throw new WebServerException("Unable to start embedded Tomcat", ex);

}

}

}

//Tomcat.java

public void start() throws LifecycleException {

getServer();

server.start();

}

//这里server.start又会回到TomcatWebServer的

public void stop() throws LifecycleException {

getServer();

server.stop();

}

//TomcatWebServer.java

//启动tomcat服务

@Override

public void start() throws WebServerException {

synchronized (this.monitor) {

if (this.started) {

return;

}

try {

addPreviouslyRemovedConnectors();

Connector connector = this.tomcat.getConnector();

if (connector != null && this.autoStart) {

performDeferredLoadOnStartup();

}

checkThatConnectorsHaveStarted();

this.started = true;

//在控制台打印这句日志，如果在yml设置了上下文，这里会打印

logger.info("Tomcat started on port(s): " + getPortsDescription(true) + " with context path '"

+ getContextPath() + "'");

}

catch (ConnectorStartFailedException ex) {

stopSilently();

throw ex;

}

catch (Exception ex) {

throw new WebServerException("Unable to start embedded Tomcat server", ex);

}

finally {

Context context = findContext();

ContextBindings.unbindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());

}

}

}

//关闭tomcat服务

@Override

public void stop() throws WebServerException {

synchronized (this.monitor) {

boolean wasStarted = this.started;

try {

this.started = false;

try {

stopTomcat();

this.tomcat.destroy();

}

catch (LifecycleException ex) {

}

}

catch (Exception ex) {

throw new WebServerException("Unable to stop embedded Tomcat", ex);

}

finally {

if (wasStarted) {

containerCounter.decrementAndGet();

}

}

}

}

附：tomcat顶层结构图

tomcat最顶层容器是Server，代表着整个服务器，一个Server包含多个Service。从上图可以看除Service主要包括多个Connector和一个Container。Connector用来处理连接相关的事情，并提供Socket到Request和Response相关转化。Container用于封装和管理Servlet，以及处理具体的Request请求。那么上文提到的Engine>Host>Context>Wrapper容器又是怎么回事呢？ 我们来看下图：

综上所述，一个tomcat只包含一个Server，一个Server可以包含多个Service，一个Service只有一个Container，但有多个Connector，这样一个服务可以处理多个连接。

      多个Connector和一个Container就形成了一个Service，有了Service就可以对外提供服务了，但是Service要提供服务又必须提供一个宿主环境，那就非Server莫属了，所以整个tomcat的声明周期都由Server控制。

总结

SpringBoot的启动主要是通过实例化SpringApplication来启动的，启动过程主要做了以下几件事情：配置属性、获取监听器，发布应用开始启动事件初、始化输入参数、配置环境，输出banner、创建上下文、预处理上下文、刷新上下文、再刷新上下文、发布应用已经启动事件、发布应用启动完成事件。在SpringBoot中启动tomcat的工作在刷新上下这一步。而tomcat的启动主要是实例化两个组件：Connector、Container，一个tomcat实例就是一个Server，一个Server包含多个Service，也就是多个应用程序，每个Service包含多个Connector和一个Container，而一个Container下又包含多个子容器。

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