SpringBoot启动流程之tomcat启动流程

我们先上图

我们下面附上源码
1.同样我们还是从SpringApplication.run(WebApplicaiton.class,args);这个入口进入。

public ConfigurableApplicationContext run(String... args) {long startTime = System.nanoTime();DefaultBootstrapContext bootstrapContext = createBootstrapContext();ConfigurableApplicationContext context = null;configureHeadlessProperty();SpringApplicationRunListeners listeners = getRunListeners(args);listeners.starting(bootstrapContext, this.mainApplicationClass);try {ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);configureIgnoreBeanInfo(environment);Banner printedBanner = printBanner(environment);context = createApplicationContext();context.setApplicationStartup(this.applicationStartup);prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);refreshContext(context);afterRefresh(context, applicationArguments);Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);if (this.logStartupInfo) {new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), timeTakenToStartup);}listeners.started(context, timeTakenToStartup);callRunners(context, applicationArguments);}catch (Throwable ex) {handleRunFailure(context, ex, listeners);throw new IllegalStateException(ex);}try {Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime);listeners.ready(context, timeTakenToReady);}catch (Throwable ex) {handleRunFailure(context, ex, null);throw new IllegalStateException(ex);}return context;
}

2.找到refreshContext方法并进入

private void refreshContext(ConfigurableApplicationContext context) {if (this.registerShutdownHook) {shutdownHook.registerApplicationContext(context);}refresh(context);
}

3.找到refresh方法并进入

protected void refresh(ConfigurableApplicationContext applicationContext) {applicationContext.refresh();
}

4.进入到AbstractApplicationContext下的refresh()

@Override
public void refresh() throws BeansException, IllegalStateException {synchronized (this.startupShutdownMonitor) {StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");// Prepare this context for refreshing.prepareRefresh();// Tell the subclass to refresh the internal bean factory.ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();// Prepare the bean factory for use in this context.prepareBeanFactory(beanFactory);try {// Allows post-processing of the bean factory in context subclasses.postProcessBeanFactory(beanFactory);StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");// Invoke factory processors registered as beans in the context.invokeBeanFactoryPostProcessors(beanFactory);// Register bean processors that intercept bean creation.registerBeanPostProcessors(beanFactory);beanPostProcess.end();// Initialize message source for this context.initMessageSource();// Initialize event multicaster for this context.initApplicationEventMulticaster();// Initialize other special beans in specific context subclasses.onRefresh();// Check for listener beans and register them.registerListeners();// Instantiate all remaining (non-lazy-init) singletons.finishBeanFactoryInitialization(beanFactory);// Last step: publish corresponding event.finishRefresh();}catch (BeansException ex) {if (logger.isWarnEnabled()) {logger.warn("Exception encountered during context initialization - " +"cancelling refresh attempt: " + ex);}// Destroy already created singletons to avoid dangling resources.destroyBeans();// Reset 'active' flag.cancelRefresh(ex);// Propagate exception to caller.throw ex;}finally {// Reset common introspection caches in Spring's core, since we// might not ever need metadata for singleton beans anymore...resetCommonCaches();contextRefresh.end();}}
}

5.我们会看到一个钩子方法，用于给子类进行扩展的方法

//钩子方法
protected void onRefresh() throws BeansException {
}

6.我们进入ServletWebServerApplicationContext下的onRefresh方法

@Override
protected void onRefresh() {super.onRefresh();try {//创建webserver容器createWebServer();}catch (Throwable ex) {throw new ApplicationContextException("Unable to start web server", ex);}
}

7.进入createWebServer方法

private void createWebServer() {WebServer webServer = this.webServer;ServletContext servletContext = getServletContext();if (webServer == null && servletContext == null) {StartupStep createWebServer = this.getApplicationStartup().start("spring.boot.webserver.create");//工厂模式 得到一个创建服务的工厂ServletWebServerFactory factory = getWebServerFactory();createWebServer.tag("factory", factory.getClass().toString());//创建一个服务器我们这里举例tomcat 看下方详情代码this.webServer = factory.getWebServer(getSelfInitializer());createWebServer.end();getBeanFactory().registerSingleton("webServerGracefulShutdown",new WebServerGracefulShutdownLifecycle(this.webServer));getBeanFactory().registerSingleton("webServerStartStop",new WebServerStartStopLifecycle(this, this.webServer));}else if (servletContext != null) {try {getSelfInitializer().onStartup(servletContext);}catch (ServletException ex) {throw new ApplicationContextException("Cannot initialize servlet context", ex);}}initPropertySources();
}

8.再进入getWebServer方法

@Override
public WebServer getWebServer(ServletContextInitializer... initializers) {if (this.disableMBeanRegistry) {Registry.disableRegistry();}Tomcat tomcat = new Tomcat();File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");tomcat.setBaseDir(baseDir.getAbsolutePath());for (LifecycleListener listener : this.serverLifecycleListeners) {tomcat.getServer().addLifecycleListener(listener);}Connector connector = new Connector(this.protocol);connector.setThrowOnFailure(true);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);//得到web的服务端return getTomcatWebServer(tomcat);
}

9.得到web的服务端

protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {return new TomcatWebServer(tomcat, getPort() >= 0, getShutdown());
}

public TomcatWebServer(Tomcat tomcat, boolean autoStart, Shutdown shutdown) {Assert.notNull(tomcat, "Tomcat Server must not be null");this.tomcat = tomcat;this.autoStart = autoStart;this.gracefulShutdown = (shutdown == Shutdown.GRACEFUL) ? new GracefulShutdown(tomcat) : null;initialize();
}

11.初始化操作

private void initialize() throws WebServerException {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())) {// Remove service connectors so that protocol binding doesn't// happen when the service is started.removeServiceConnectors();}});// Start the server to trigger initialization listeners//启动tomcatthis.tomcat.start();// We can re-throw failure exception directly in the main threadrethrowDeferredStartupExceptions();try {ContextBindings.bindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());}catch (NamingException ex) {// Naming is not enabled. Continue}// Unlike Jetty, all Tomcat threads are daemon threads. We create a// blocking non-daemon to stop immediate shutdown//创建一个阻塞的非守护进程来停止立即关闭startDaemonAwaitThread();}catch (Exception ex) {stopSilently();destroySilently();throw new WebServerException("Unable to start embedded Tomcat", ex);}}
}

12.启动tomcat

private void startDaemonAwaitThread() {Thread awaitThread = new Thread("container-" + (containerCounter.get())) {@Overridepublic void run() {TomcatWebServer.this.tomcat.getServer().await();}};awaitThread.setContextClassLoader(getClass().getClassLoader());awaitThread.setDaemon(false);awaitThread.start();
}

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