DispatcherServlet是由Spring创建，初始化是由Tomcat；

初始化时机

默认第一次调用初始化；

@Configuration
@ComponentScan
@PropertySource("classpath:application.properties")
@EnableConfigurationProperties({WebMvcProperties.class, ServerProperties.class})//绑定配置类中键值spring.mvc.servlet
public class WebConfig {

    // 内嵌web容器工厂
    @Bean
    public TomcatServletWebServerFactory tomcatServletWebServerFactory(ServerProperties serverProperties) {
        return new TomcatServletWebServerFactory(serverProperties.getPort());
    }

    // 创建DispatcherServlet
    @Bean
    public DispatcherServlet dispatcherServlet(){
        return new DispatcherServlet();
    }

    // 注册DispatcherServlet,SpringMVC的入口
    @Bean
    public DispatcherServletRegistrationBean dispatcherServletRegistrationBean(DispatcherServlet dispatcherServlet,
                                                                               WebMvcProperties webMvcProperties){
        DispatcherServletRegistrationBean registrationBean = new DispatcherServletRegistrationBean(dispatcherServlet, "/");
//        registrationBean.setLoadOnStartup(1);//>0就在tomcat启动时就初始化，否则第一次调用初始化
        registrationBean.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
        return registrationBean;
    }
    
}

初始化执行操作

调用DispatcherServlet类中的onRefresh方法；

protected void onRefresh(ApplicationContext context) {
    this.initStrategies(context);
}

protected void initStrategies(ApplicationContext context) {
    this.initMultipartResolver(context);// 初始化文件上传解析器
    this.initLocaleResolver(context);
    this.initThemeResolver(context);
    
    this.initHandlerMappings(context);// 路径映射
    this.initHandlerAdapters(context);// 请求处理 适配器
    this.initHandlerExceptionResolvers(context);// 解析异常
    
    this.initRequestToViewNameTranslator(context);
    this.initViewResolvers(context);
    this.initFlashMapManager(context);
}

处理器映射器

RequestMappingHandlerMapping

负责找到请求 对应的控制器方法；

不使用DispatcherServlet初始化时默认添加的组件，只会将RequestMappingHandlerMapping作为DispatcherServlet的成员变量，不会作为Bean；

DispatcherServlet.properties：

org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping,\
	org.springframework.web.servlet.function.support.RouterFunctionMapping

org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
	org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter,\
	org.springframework.web.servlet.function.support.HandlerFunctionAdapter

webConfig中：

// 如果用 DispatcherServlet 初始化时默认添加的组件, 并不会作为 bean
@Bean
public RequestMappingHandlerMapping requestMappingHandlerMapping(){
    return new RequestMappingHandlerMapping();
}

添加Controller：

@Controller
public class Controller1 {
    private static final Logger log = LoggerFactory.getLogger(Controller1.class);

    @GetMapping("/test1")
    public ModelAndView test1() throws Exception {
        log.debug("test1()");
        return null;
    }

    @PostMapping("/test2")
    public ModelAndView test2(@RequestParam("name") String name) {
        log.debug("test2({})", name);
        return null;
    }

}

测试：

public class Dispatcher_test {
    private static final Logger log = LoggerFactory.getLogger(Dispatcher_test.class);

    public static void main(String[] args) throws Exception {
        AnnotationConfigServletWebServerApplicationContext context =
                new AnnotationConfigServletWebServerApplicationContext(WebConfig.class);
        // 作用 解析 @RequestMapping 以及派生注解，生成路径与控制器方法的映射关系,在初始化时就生成
        RequestMappingHandlerMapping handlerMapping = context.getBean(RequestMappingHandlerMapping.class);
        // 获取映射结果
        Map<RequestMappingInfo, HandlerMethod> handlerMethods = handlerMapping.getHandlerMethods();
        handlerMethods.forEach((k, v) -> {
            System.out.println(k + "=" + v);
        });

        // 请求过来，获取控制器方法，返回处理器执行链对象
        MockHttpServletRequest request = new MockHttpServletRequest("GET", "/test1");
        MockHttpServletResponse response = new MockHttpServletResponse();
        HandlerExecutionChain chain = handlerMapping.getHandler(request);
        System.out.println(chain);
    }
}

{GET [/test1]}=com.Nreal.MVC.dispatcher.Controller1#test1()
{POST [/test2]}=com.Nreal.MVC.dispatcher.Controller1#test2(String)
HandlerExecutionChain with [com.Nreal.MVC.dispatcher.Controller1#test1()] and 0 interceptors

处理器适配器

调用控制器方法；

RequestMappingHandlerAdapter中invokeHandlerMethod为protected，其它类想要调用可以创建其子类修改访问修饰符；

public class MyRequestMappingHandlerAdapter extends RequestMappingHandlerAdapter {
    @Override
    public ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
        return super.invokeHandlerMethod(request, response, handlerMethod);
    }
}

webConfig中：

@Bean
public RequestMappingHandlerAdapter requestMappingHandlerAdapter() {
    return new MyRequestMappingHandlerAdapter();
}

测试代码全部：

public class Dispatcher_test {
    private static final Logger log = LoggerFactory.getLogger(Dispatcher_test.class);

    public static void main(String[] args) throws Exception {
        AnnotationConfigServletWebServerApplicationContext context =
                new AnnotationConfigServletWebServerApplicationContext(WebConfig.class);
        // 作用 解析 @RequestMapping 以及派生注解，生成路径与控制器方法的映射关系,在初始化时就生成
        RequestMappingHandlerMapping handlerMapping = context.getBean(RequestMappingHandlerMapping.class);
        // 获取映射结果
        Map<RequestMappingInfo, HandlerMethod> handlerMethods = handlerMapping.getHandlerMethods();
        handlerMethods.forEach((k, v) -> {
            System.out.println(k + "=" + v);
        });

        // 请求过来，获取控制器方法，返回处理器执行链对象
        MockHttpServletRequest request = new MockHttpServletRequest("GET", "/test1");
        MockHttpServletResponse response = new MockHttpServletResponse();
        HandlerExecutionChain chain = handlerMapping.getHandler(request);
        System.out.println(chain);

        System.out.println(">>>>>>>>>>>>>>>>>>>>>");

        // HandlerAdapter作用:调用控制器方法
        MyRequestMappingHandlerAdapter handlerAdapter = context.getBean(MyRequestMappingHandlerAdapter.class);
        handlerAdapter.invokeHandlerMethod(request, response, (HandlerMethod) chain.getHandler());

        System.out.println(">>>>>>>>>>>>>>>>>>>>> 所有参数解析器");
        for (HandlerMethodArgumentResolver resolver : handlerAdapter.getArgumentResolvers()) {
            System.out.println(resolver);
        }

        System.out.println(">>>>>>>>>>>>>>>>>>>>> 所有返回值解析器");
        for (HandlerMethodReturnValueHandler handler : handlerAdapter.getReturnValueHandlers()) {
            System.out.println(handler);
        }
    }
}