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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。Java知音公众号内回复“后端面试”，送你一份Java面试题宝典
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。