SpringBoot中Tomcat是如何启动的

Copyprotected void onRefresh() {
    super.onRefresh();
    try {
        this.createWebServer();
    } catch (Throwable var2) {
        throw new ApplicationContextException("Unable to start web server", var2);
    }
}

Copypublic class ServletWebServerApplicationContext extends GenericWebApplicationContext implements ConfigurableWebServerApplicationContext {
    //...省略部分代码
    public static final String DISPATCHER_SERVLET_NAME = "dispatcherServlet";
    //内嵌容器
    private volatile WebServer webServer;
    private ServletConfig servletConfig;
   
    //...省略部分代码
    //创建Web容器
    private void createWebServer() {
        WebServer webServer = this.webServer;
        ServletContext servletContext = this.getServletContext();
        //webServer和servletContext都是null，表示还没创建容器，进入创建容器的逻辑
        if (webServer == null && servletContext == null) {
            //获取创建容器的工厂，可以通过WebServerFactoryCustomizer接口对这个工厂进行自定义设置
            ServletWebServerFactory factory = this.getWebServerFactory();
            //具体的创建容器的方法，我们进去具体看下
            this.webServer = factory.getWebServer(new ServletContextInitializer[]{this.getSelfInitializer()});
        } else if (servletContext != null) {
            try {
                this.getSelfInitializer().onStartup(servletContext);
            } catch (ServletException var4) {
                throw new ApplicationContextException("Cannot initialize servlet context", var4);
            }
        }
        this.initPropertySources();
    }
}

Copypublic class TomcatServletWebServerFactory的getWebServer{
//...

@Override
public WebServer getWebServer(ServletContextInitializer... initializers) {
    //创建Tomcat容器
    Tomcat tomcat = new Tomcat();
    File baseDir = (this.baseDirectory != null ? this.baseDirectory
            : createTempDir("tomcat"));
    tomcat.setBaseDir(baseDir.getAbsolutePath());
    //创建连接器，默认NIO模式，可以通过WebServerFactoryCustomizer改变具体模式
    Connector connector = new Connector(this.protocol);
    tomcat.getService().addConnector(connector);
    //自定义连接器
    customizeConnector(connector);
    tomcat.setConnector(connector);
    tomcat.getHost().setAutoDeploy(false);
    configureEngine(tomcat.getEngine());
    //可以通过WebServerFactoryCustomizer添加额外的连接器，这边将这些连接器绑定到Tomcat
    for (Connector additionalConnector : this.additionalTomcatConnectors) {
        tomcat.getService().addConnector(additionalConnector);
    }
    //组测Listener、Filter和Servlet，自定义Context等操作
    //这个方法可以重点看下
    prepareContext(tomcat.getHost(), initializers);
    //创建TomcatWebServer，并调用start方法
    return getTomcatWebServer(tomcat);
}

//内嵌的Tomcat容器
public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
  Assert.notNull(tomcat, "Tomcat Server must not be null");
  this.tomcat = tomcat;
  this.autoStart = autoStart;
        //这边触发Tomcat的启动流程，是Tomcat启动的入口点
  initialize();
}
//...省略部分代码
}

Copy@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass(DispatcherServlet.class)
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)
@EnableConfigurationProperties(ServerProperties.class)
public class DispatcherServletAutoConfiguration {

 /*
  * The bean name for a DispatcherServlet that will be mapped to the root URL "/"
  */
 public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";

 /*
  * The bean name for a ServletRegistrationBean for the DispatcherServlet "/"
  */
 public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration";

 @Configuration
 @Conditional(DefaultDispatcherServletCondition.class)
 @ConditionalOnClass(ServletRegistration.class)
 @EnableConfigurationProperties(WebMvcProperties.class)
 protected static class DispatcherServletConfiguration {

  private final WebMvcProperties webMvcProperties;

  public DispatcherServletConfiguration(WebMvcProperties webMvcProperties) {
   this.webMvcProperties = webMvcProperties;
  }

  @Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
  public DispatcherServlet dispatcherServlet() {
   DispatcherServlet dispatcherServlet = new DispatcherServlet();
   dispatcherServlet.setDispatchOptionsRequest(
     this.webMvcProperties.isDispatchOptionsRequest());
   dispatcherServlet.setDispatchTraceRequest(
     this.webMvcProperties.isDispatchTraceRequest());
   dispatcherServlet.setThrowExceptionIfNoHandlerFound(
     this.webMvcProperties.isThrowExceptionIfNoHandlerFound());
   return dispatcherServlet;
  }

  @Bean
  @ConditionalOnBean(MultipartResolver.class)
  @ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
  public MultipartResolver multipartResolver(MultipartResolver resolver) {
   // Detect if the user has created a MultipartResolver but named it incorrectly
   return resolver;
  }

 }

 @Configuration
 @Conditional(DispatcherServletRegistrationCondition.class)
 @ConditionalOnClass(ServletRegistration.class)
 @EnableConfigurationProperties(WebMvcProperties.class)
 @Import(DispatcherServletConfiguration.class)
 protected static class DispatcherServletRegistrationConfiguration {

  private final ServerProperties serverProperties;

  private final WebMvcProperties webMvcProperties;

  private final MultipartConfigElement multipartConfig;

  public DispatcherServletRegistrationConfiguration(
    ServerProperties serverProperties, WebMvcProperties webMvcProperties,
    ObjectProvider<MultipartConfigElement> multipartConfigProvider) {
   this.serverProperties = serverProperties;
   this.webMvcProperties = webMvcProperties;
   this.multipartConfig = multipartConfigProvider.getIfAvailable();
  }

        //很熟悉的代码有没有，ServletRegistrationBean就是我们上一节中介绍的注册Servlet的方式
        //只不过这边注册的是DispatcherServlet这个特殊的Servlet
  @Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
  @ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
  public ServletRegistrationBean<DispatcherServlet> dispatcherServletRegistration(
    DispatcherServlet dispatcherServlet) {
   ServletRegistrationBean<DispatcherServlet> registration = new ServletRegistrationBean<>(
     dispatcherServlet,
     this.serverProperties.getServlet().getServletMapping());
   registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
   registration.setLoadOnStartup(
     this.webMvcProperties.getServlet().getLoadOnStartup());
   if (this.multipartConfig != null) {
    registration.setMultipartConfig(this.multipartConfig);
   }
   return registration;
  }

 }

//...省略部分代码
}

Copyserver:
  port: ${port:9999}
  tomcat:
    accept-count: 200
    #最好进行这段配置，默认会在tmp目录下创建，Linux有时会有定时任务删除tmp目录下的内容
    basedir: my-tomcat
    accesslog:
      enabled: true
      pattern: '%t %a "%r" %s %S (%b M) (%D ms)'
      max-http-post-size: 2MB
      max-swallow-size: 2M
    uri-encoding: GBK
    threads:
      max: 100
      min-spare: 10