1、DisptachServlet的注册原理

（1）自动配置DisptcherServletAutoConfiguration

  1. @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
  2. @Configuration(proxyBeanMethods = false)
  3. @ConditionalOnWebApplication(type = Type.SERVLET)
  4. @ConditionalOnClass(DispatcherServlet.class)
  5. @AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)
  6. public class DispatcherServletAutoConfiguration {

（2）容器中注册了一个组件DsipatcherServlet

  1.         @Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
  2.         public DispatcherServlet dispatcherServlet(WebMvcProperties webMvcProperties) {
  3.             DispatcherServlet dispatcherServlet = new DispatcherServlet();
  4.             dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest());
  5.             dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest());
  6.             dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound());
  7.             dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents());
  8.             dispatcherServlet.setEnableLoggingRequestDetails(webMvcProperties.isLogRequestDetails());
  9.             return dispatcherServlet;
  10.         }

（3）容器中又使用DispatcherServletRegistrationBean向容器中注册了DispatcherServlet

  1.         @Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
  2.         @ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
  3.         public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet,
  4.                 WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
  5.             DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,
  6.                     webMvcProperties.getServlet().getPath());
  7.             registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
  8.             registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
  9.             multipartConfig.ifAvailable(registration::setMultipartConfig);
  10.             return registration;
  11.         }

  • 1、发现匹配的路径webMvcProperties.getServlet().getPath()=”/“

    public static class Servlet {

      /**
       * Path of the dispatcher servlet. Setting a custom value for this property is not
       * compatible with the PathPatternParser matching strategy.
       */
      private String path = "/";

  • Tomcat-Servlet在匹配路径的时候 如果有多个Servlet可以匹配路径的时候，使用精确匹配优先。

    2、原理

    • SpringBoot应用启动发现当前是Web应用，web场景有有tomcat包
    • web应用创建一个web版的ioc容器ServletWebServerApplicationContext
    • ServletWebServerApplicationContext启动的时候寻找ServletWebServerFactory(Servlet的web服务器工厂->Servlet的web服务器)
    • SpringBoot底层默认有很多的WebServlet服务器工厂TomcatServletWebServerFactory, JettyServletWebServerFactory,or UndertowServletWebServerFactory
    • 底层直接会有一个配置类ServletWebServerFactoryAutoConfiguration
    • ServletWebServerFactoryAutoConfiguration导入了ServletWebServerFactoryConfiguration（配置类）
    • ServletWebServerFactoryConfiguration配置类，genuine动态判断系统中到底导入了哪个Web服务器的包（默认是web-starter导入的是Tomcat服务器），容器中就有TomcatServletWebServerFactory
    • TomcatServletWebServerFactory中创建出Tomcat服务器
    • 内嵌服务器，就是手动把启动武器的代码调用（tomcat核心jar要包含进来）
      @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());
   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);
   return getTomcatWebServer(tomcat);
}

      3、切换内置服务器

      （1）查到响应的服务器启动环境
      https://docs.spring.io/spring-boot/docs/current/reference/html/using.html#using.build-systems.starters
      spring-boot-starter-undertow
      （2）修改pom.xml配置文件，先排除tomcat，再导入对于的服务器
         <dependency>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-starter-web</artifactId>
       <exclusions>
           <exclusion>
               <groupId>org.springframework.boot</groupId>
               <artifactId>spring-boot-starter-tomcat</artifactId>
           </exclusion>
       </exclusions>
   </dependency>
   <dependency>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-starter-undertow</artifactId>
   </dependency>

      3、定制Servlet容器

  • 实现 WebServerFactoryCustomizer

  • 修改配置文件server.xxx（推荐）
  • 自定义ConfigurationServletFactory