Springboot集成mongodbtemplate springboot集成tomcat

前言

不得不说SpringBoot的开发者是在为大众程序员谋福利，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

@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？

org.springframework.boot    spring-boot-starter-web        org.springframework.boot            spring-boot-starter-tomcat        javax.servlet    javax.servlet-api    3.1.0provided

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 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logoBanner 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AbstractServletWebServerFactoryJettyServletWebServerFactoryTomcatServletWebServerFactoryUndertowServletWebServerFactory

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();}}}}

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。从上图可以看出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。