<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-webmvc</artifactId>
    <version>5.3.4</version>
</dependency>

<!--Context 加載監(jiān)聽器 -->
<listener>
     <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<servlet>
     <servlet-name>dispatcherServlet</servlet-name>
     <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
     <init-param>
     	 <param-name>contextConfigLocation</param-name>
         <param-value>classpath:application.xml</param-value>
     </init-param>
     <!--Web服務器一旦啟動，Servlet就會實例化創(chuàng)建對象，然后初始化(預備創(chuàng)建對象)-->
     <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>dispatcherServlet</servlet-name>
    <url-pattern>/</url-pattern>
</servlet-mapping>

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
                           http://www.springframework.org/schema/beans/spring-beans.xsd
                           http://www.springframework.org/schema/context
                           http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/mvc https://www.springframework.org/schema/mvc/spring-mvc.xsd">
    <!--配置spring包掃描路徑，被@Component、@Controller、@Service、@Repository標注的類都會交由Spring托管一個Bean-->
    <context:component-scan base-package="com.ybe.*"/>
    <!--配置視圖解析器-->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/"/>
        <property name="suffix" value=".jsp"></property>
    </bean>
</beans>

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
                           http://www.springframework.org/schema/beans/spring-beans.xsd
                           http://www.springframework.org/schema/context
                           http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/mvc https://www.springframework.org/schema/mvc/spring-mvc.xsd">
</beans>

package com.ybe.controller;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
@Controller
public class HelloController {

    @RequestMapping("/hello")
    public String helloWorld(){
        System.out.println("hello world");
        return "index";
    }
}

// 初始化 MultipartResolver:主要用來處理文件上傳.如果定義過當前類型的bean對象，那么直接獲取，如果沒有的話，可以為null
initMultipartResolver(context);
// 初始化 LocaleResolver:主要用來處理國際化配置,基于URL參數(shù)的配置(AcceptHeaderLocaleResolver)，基于session的配置(SessionLocaleResolver)，基于cookie的配置(CookieLocaleResolver)
initLocaleResolver(context);
// 初始化 ThemeResolver:主要用來設置主題Theme
initThemeResolver(context);
// 初始化 HandlerMapping:映射器，用來將對應的request跟controller進行對應
initHandlerMappings(context);
// 初始化 HandlerAdapter:處理適配器，主要包含Http請求處理器適配器，簡單控制器處理器適配器，注解方法處理器適配器
initHandlerAdapters(context);
// 初始化 HandlerExceptionResolver:基于HandlerExceptionResolver接口的異常處理
initHandlerExceptionResolvers(context);
// 初始化 RequestToViewNameTranslator:當controller處理器方法沒有返回一個View對象或邏輯視圖名稱，并且在該方法中沒有直接往response的輸出流里面寫數(shù)據(jù)的時候，spring將會采用約定好的方式提供一個邏輯視圖名稱
initRequestToViewNameTranslator(context);
// 初始化 ViewResolver: 將ModelAndView選擇合適的視圖進行渲染的處理器
initViewResolvers(context);
// 初始化 FlashMapManager: 提供請求存儲屬性，可供其他請求使用
initFlashMapManager(context);

# Default implementation classes for DispatcherServlet's strategy interfaces.
# Used as fallback when no matching beans are found in the DispatcherServlet context.
# Not meant to be customized by application developers.
org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver
org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver

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
    org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver,org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver

org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator

org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver

org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager

protected void initHandlerMethods() {
    // 遍歷 Bean ，逐個處理
    for (String beanName : getCandidateBeanNames()) {
        // 排除目標代理類，AOP 相關，可查看注釋
        if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
            // 處理 Bean
            processCandidateBean(beanName);
        }
    }
    // 初始化處理器的方法們，目前沒有特殊業(yè)務邏輯，只是打印日志
    handlerMethodsInitialized(getHandlerMethods());
}

@Override
public void afterPropertiesSet() {
    // Do this first, it may add ResponseBody advice beans
    // 初始化注釋了@ControllerAdvice的類的相關屬性
    initControllerAdviceCache();

    // 初始化 argumentResolvers 屬性
    if (this.argumentResolvers == null) {
        List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
        this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
    }
    // 初始化 initBinderArgumentResolvers 屬性
    if (this.initBinderArgumentResolvers == null) {
        List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
        this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
    }
    // 初始化 returnValueHandlers 屬性
    if (this.returnValueHandlers == null) {
        List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
        this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
    }
}

protected void initApplicationContext() throws BeansException {
    // 空實現(xiàn)，交給子類實現(xiàn)，用于注冊自定義的攔截器到interceptors中，目前暫無子類實現(xiàn)
    extendInterceptors(this.interceptors);
    // 掃描已注冊的MappedInterceptor的Bean們，添加到adaptedInterceptors中
    detectMappedInterceptors(this.adaptedInterceptors);
    // 將interceptors初始化成 HandlerInterceptor類型，添加到adaptedInterceptors中
    initInterceptors();
}

protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
    if (this.handlerMappings != null) {
        //遍歷
        for (HandlerMapping mapping : this.handlerMappings) {
            HandlerExecutionChain handler = mapping.getHandler(request);
            if (handler != null) {
                return handler;
            }
        }
    }
    return null;
}

Object handler = getHandlerInternal(request);
if (handler == null) {
	handler = getDefaultHandler();
}
// 如果handler為null 即返回null。說明當前的處理器映射器不匹配。
if (handler == null) {
	return null;
}
// Bean name or resolved handler?
if (handler instanceof String) {
    String handlerName = (String) handler;
    handler = obtainApplicationContext().getBean(handlerName);
}

// Ensure presence of cached lookupPath for interceptors and others
if (!ServletRequestPathUtils.hasCachedPath(request)) {
	initLookupPath(request);
}
//創(chuàng)建處理器鏈
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);

protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
    if (this.handlerAdapters != null) {
        //循環(huán)判斷哪個適配器能處理傳入的處理器
        for (HandlerAdapter adapter : this.handlerAdapters) {
            if (adapter.supports(handler)) {
                return adapter;
            }
        }
    }
    throw new ServletException("No adapter for handler [" + handler +
                               "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}

protected View resolveViewName(String viewName, @Nullable Map<String, Object> model,
                               Locale locale, HttpServletRequest request) throws Exception {
    if (this.viewResolvers != null) {
        for (ViewResolver viewResolver : this.viewResolvers) {
            View view = viewResolver.resolveViewName(viewName, locale);
            if (view != null) {
                return view;
            }
        }
    }
    return null;
}

public void render(@Nullable Map<String, ?> model, HttpServletRequest request,
                   HttpServletResponse response) throws Exception {
    if (logger.isDebugEnabled()) {
        logger.debug("View " + formatViewName() +
                     ", model " + (model != null ? model : Collections.emptyMap()) +
                     (this.staticAttributes.isEmpty() ? "" : ", static attributes " + this.staticAttributes));
    }
    //合并返回結果，將 Model 中的靜態(tài)數(shù)據(jù)和請求中的動態(tài)數(shù)據(jù)進行合并
    Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
    prepareResponse(request, response);
    //進行渲染
    renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
}