秋刀鱼足迹
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SpringBoot内置tomcat启动原理
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。
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> <version>2.1.6.RELEASE</version> </dependency>
@SpringBootApplicationpublic 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？
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> <!-- 移除嵌入式tomcat插件 --> <exclusions> <exclusion> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-tomcat</artifactId> </exclusion> </exclusions> </dependency> <!--添加servlet-api依赖---> <dependency> <groupId>javax.servlet</groupId> <artifactId>javax.servlet-api</artifactId> <version>3.1.0</version> <scope>provided</scope> </dependency>
更新main函数，主要是继承SpringBootServletInitializer，并重写configure()方法。
@SpringBootApplicationpublic 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ConfigurableApplicationContextpublic static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {return (new SpringApplication(primarySources)).run(args);
}
public ConfigurableApplicationContext run(String... args) {
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> 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.javapublic 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ServletWebServerFactoryprivate 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。@Overridepublic 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TomcatWebServerpublic 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.javapublic 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@Overridepublic 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@Overridepublic 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();
}
}
}
}
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。