基于源码看Tomcat 在 SpringBoot 中的启动

@SpringBootApplicationpublicclass TomcatdebugApplication {
    public static void main(String[] args) {        SpringApplication.run(TomcatdebugApplication.class, args);    }
}

public ConfigurableApplicationContext run(String... args) {    StopWatch stopWatch = new StopWatch();    stopWatch.start();    ConfigurableApplicationContext context = null;    CollectionexceptionReporters = new ArrayList<>();    //设置系统属性『java.awt.headless』，为true则启用headless模式支持    configureHeadlessProperty();    //通过*SpringFactoriesLoader*检索*META-INF/spring.factories*，       //找到声明的所有SpringApplicationRunListener的实现类并将其实例化，       //之后逐个调用其started()方法，广播SpringBoot要开始执行了    SpringApplicationRunListeners listeners = getRunListeners(args);    //发布应用开始启动事件    listeners.starting();    try {    //初始化参数      ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);      //创建并配置当前SpringBoot应用将要使用的Environment（包括配置要使用的PropertySource以及Profile）,        //并遍历调用所有的SpringApplicationRunListener的environmentPrepared()方法，广播Environment准备完毕。      ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);      configureIgnoreBeanInfo(environment);      //打印banner      Banner printedBanner = printBanner(environment);      //创建应用上下文      context = createApplicationContext();      //通过*SpringFactoriesLoader*检索*META-INF/spring.factories*，获取并实例化异常分析器      exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,          new Class[] { ConfigurableApplicationContext.class }, context);      //为ApplicationContext加载environment，之后逐个执行ApplicationContextInitializer的initialize()方法来进一步封装ApplicationContext，        //并调用所有的SpringApplicationRunListener的contextPrepared()方法，【EventPublishingRunListener只提供了一个空的contextPrepared()方法】，        //之后初始化IoC容器，并调用SpringApplicationRunListener的contextLoaded()方法，广播ApplicationContext的IoC加载完成，        //这里就包括通过**@EnableAutoConfiguration**导入的各种自动配置类。      prepareContext(context, environment, listeners, applicationArguments, printedBanner);      //刷新上下文      refreshContext(context);      //再一次刷新上下文,其实是空方法，可能是为了后续扩展。      afterRefresh(context, applicationArguments);      stopWatch.stop();      if (this.logStartupInfo) {        new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);      }      //发布应用已经启动的事件      listeners.started(context);      //遍历所有注册的ApplicationRunner和CommandLineRunner，并执行其run()方法。        //我们可以实现自己的ApplicationRunner或者CommandLineRunner，来对SpringBoot的启动过程进行扩展。      callRunners(context, applicationArguments);    }    catch (Throwable ex) {      handleRunFailure(context, ex, exceptionReporters, listeners);      throw new IllegalStateException(ex);    }
    try {    //应用已经启动完成的监听事件      listeners.running(context);    }    catch (Throwable ex) {      handleRunFailure(context, ex, exceptionReporters, null);      throw new IllegalStateException(ex);    }    return context;  }

protected ConfigurableApplicationContext createApplicationContext() {    Class contextClass = this.applicationContextClass;    if (contextClass == null) {      try {        switch (this.webApplicationType) {        case SERVLET:          contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);          break;        case REACTIVE:          contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);          break;        default:          contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);




    
        }      }      catch (ClassNotFoundException ex) {        thrownew IllegalStateException(            "Unable create a default ApplicationContext, " + "please specify an ApplicationContextClass",            ex);      }    }    return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);  }

//类：SpringApplication.java
private void refreshContext(ConfigurableApplicationContext context) {    //直接调用刷新方法    refresh(context);    if (this.registerShutdownHook) {      try {        context.registerShutdownHook();      }      catch (AccessControlException ex) {        // Not allowed in some environments.      }    }  }//类：SpringApplication.java
protected void refresh(ApplicationContext applicationContext) {    Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);    ((AbstractApplicationContext) applicationContext).refresh();  }

// 类：AbstractApplicationContextpublic void refresh() throws BeansException, IllegalStateException {    synchronized (this.startupShutdownMonitor) {      // 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);
        // Invoke factory processors registered as beans in the context.        invokeBeanFactoryPostProcessors(beanFactory);
        // Register bean processors that intercept bean creation.        registerBeanPostProcessors(beanFactory);
        // Initialize message source for this context.        initMessageSource();
        // Initialize event multicaster for this context.        initApplicationEventMulticaster();
        // Initialize other special beans in specific context subclasses.这里的意思就是调用各个子类的onRefresh()        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();      }    }  }

//类：ServletWebServerApplicationContextprotected void onRefresh() {    super.onRefresh();    try {      createWebServer();    }    catch (Throwable ex) {      thrownew ApplicationContextException("Unable to start web server", ex);    }  }
private void createWebServer() {    WebServer webServer = this.webServer;    ServletContext servletContext = getServletContext();    if (webServer == null && servletContext == null) {      ServletWebServerFactory factory = getWebServerFactory();      this




    
.webServer = factory.getWebServer(getSelfInitializer());    }    elseif (servletContext != null) {      try {        getSelfInitializer().onStartup(servletContext);      }      catch (ServletException ex) {        thrownew ApplicationContextException("Cannot initialize servlet context", ex);      }    }    initPropertySources();  }

@Override  public WebServer getWebServer(ServletContextInitializer... initializers) {    Tomcat tomcat = new Tomcat();    File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");    tomcat.setBaseDir(baseDir.getAbsolutePath());    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);  }

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;    }

/** If used, an Engine is always the top level Container in a Catalina * hierarchy. Therefore, the implementation's setParent() method * should throw IllegalArgumentException. * * @author Craig R. McClanahan */publicinterface Engine extends Container {    //省略代码}/** *
 * The parent Container attached to a Host is generally an Engine, but may * be some other implementation, or may be omitted if it is not necessary. *

 * The child containers attached to a Host are generally implementations * of Context (representing an individual servlet context). * * @author Craig R. McClanahan */public interface Host extends Container {//省略代码
}/*** 

 * The parent Container attached to a Context is generally a Host, but may * be some other implementation, or may be omitted if it is not necessary. *

 * The child containers attached to a Context are generally implementations * of Wrapper (representing individual servlet definitions). *

 * * @author Craig R. McClanahan */public interface Context extends Container, ContextBind {    //省略代码}/**

 * The parent Container attached to a Wrapper will generally be an * implementation of Context, representing the servlet context (and * therefore the web application) within which this servlet executes. *

 * Child Containers are not allowed on Wrapper implementations, so the * addChild() method should throw an * IllegalArgumentException. * * @author Craig R. McClanahan */publicinterface Wrapper extends Container {
    //省略代码}

//部分源码，其余部分省略。publicclass Tomcat {//设置连接器     public void setConnector(Connector connector) {        Service service = getService();        boolean found = false;        for (Connector serviceConnector : service.findConnectors()) {            if (connector == serviceConnector) {                found = true;            }        }        if (!found) {            service.addConnector(connector);        }    }    //获取service       public Service getService() {        return getServer().findServices()[0];    }    //设置Host容器     public void setHost(Host host) {        Engine engine = getEngine();        boolean found = false;        for (Container engineHost : engine.findChildren()) {            if (engineHost == host) {                found = true;            }        }        if (!found) {            engine.addChild(host);        }    }    //获取Engine容器     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;    }    //获取server       public Server getServer() {
        if (server != null) {            return server;        }
        System.setProperty("catalina.useNaming", "false");
        server = new StandardServer();
        initBaseDir();
        // Set configuration source        ConfigFileLoader.setSource(new CatalinaBaseConfigurationSource(new File(basedir), null));
        server.setPort( -1 );
        Service service = new StandardService();        service.setName("Tomcat");        server.addService(service);        return server;    }
    //添加Context容器      public Context addContext(Host host, String contextPath, String contextName,            String dir) {        silence(host, contextName);        Context ctx = createContext(host, contextPath);