图文源码分析Spring MVC请求映射原理、执行流程

约定不等于承诺〃 2023-09-30 05:51 17阅读 0赞

#### 文章目录 ####

*   *  一、Spring MVC执行流程（总结）
     *   *  以GET请求为例：
     *  二、源码分析请求映射原理/执行流程
     *   *  1）doService()
         *  2）doDispatch()
         *  3）getHandler()
         *   *  getHandler()方法是如何获取到具体的HandlerExecutionChain的？
         *  4）getHandlerAdapter()
         *  5）HandlerAdapter\#handle()
         *  6）RequestHandlerMethodAdapter\#invokeHandlerMethod()
         *  processDispatchResult()

### 一、Spring MVC执行流程（总结） ###

![请添加图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA56eD5aS054ix5YGl6Lqr_size_20_color_FFFFFF_t_70_g_se_x_16]

1.  客户端的所有请求都会交给前端控制器`DispatcherServlet`来处理，`DispatcherServlet`会负责调用系统的其他模块来完成用户请求的处理；
2.  即用户发送的请求会先从**`DispatcherServlet`的`doService()`方法**开始；在该方法中会先将webApplicationContext、localeResolver、themeResolver等对象添加到request请求的attribute属性中，接着调用doDispatch()方法；
3.  进入到**doDispatch()方法**中：
    
    1.  首先**检查请求是否为文件的上传/下载请求**（校验的规则是：是否是post并且contenttType是否以multipart为前缀），如果是则将请求包装成`MultipartHttpServletRequest`；
    2.  其次调用**getHandler()**方法**从五个HandlerMapping中找到相应的`HandlerMapping`对象**（以普通HTTP请求为例，HandlerMapping为requestMappingHandlerMapping），**进而获取到该Handler对应的处理链`HandlerExecutionChain`对象**；
    3.  其实在获取`HandlerExecutionChain`时，其内部也获取到了Spring自带的以及我们自定义的MVC拦截器；
    4.  然后通过上面获取到的`HandlerExecutionChain`对象，进而从四个`HandlerAdapter`中获取相应的`HandlerAdapter`处理器适配器（HandlerAdapter是一个适配器，它用统一的接口对各种Handler中的方法进行调用）。
    5.  执行处理链`HandlerExecutionChain`中全部**拦截器的preHandle()**方法，如果返回FALSE，则执行处理链中所有拦截器的afterCompletion()方法并立即返回。
    6.  接着**调用`handlerAdapter`对象的`handle()`方法来执行Controller中的方法；**
        
        1> 其中会获取26个参数解析器`HandlerMethodArgumentResolver`，15个返回值处理器`HandlerMethodReturnValueHandler`；
        
        2> 最后**通过反射，打开Controller相应方法的访问权限，进而调用相应的方法**；
    7.  HandlerAdapter执行完，返回一个ModelAndView给DispatcherServlet；并执行**拦截器的postHandle()**方法；如果出现异常，则有HandlerExceptionHandler处理异常，得到新的ModelAndView对象；
    8.  由于ModelAndView的视图是逻辑视图，DispatcherServlet还要借助**ViewResolver完成从逻辑视图到真实视图对象的解析工作**；
    9.  当得到真正的View视图后，DispatcherServlet会利用这个View视图对象对模型数据ModelAndView进行渲染；
    10. 调用处理链中所有**拦截器的afterCompletion()方法**；
    11. 客户端得到响应，可能是一个普通的HTML页面，也可以是XML或JSON字符串，还可以是一张图片或者一个PDF文件。

**注：在整个SpringMVC的执行流程中，大量使用了模板方法，比如：HandlerAdapter\#handle()方法（具体的handleInternal()逻辑由子类实现），FrameServlet\#processRequest()方法（具体的doService()逻辑由子类实现）**

#### 以GET请求为例： ####

@RestController
    public class TestController {
        
        @GetMapping("/hello")
        public String hello() {
        
            return "hello";
        }
    }

![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA56eD5aS054ix5YGl6Lqr_size_20_color_FFFFFF_t_70_g_se_x_16 1]

### 二、源码分析请求映射原理/执行流程 ###

HTTP请求的入口为DispatcherServlet，`DispatcherServlet`继承自`FrameworkServlet`，在`FrameworkServlet`的doGet()方法便是GET请求的入口。

![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA56eD5aS054ix5YGl6Lqr_size_20_color_FFFFFF_t_70_g_se_x_16 2]

无论是doGet()、doPost()、doPut()、doDelete()都会进入到`processRequest(request, response)`方法处理请求。

protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        
    
        long startTime = System.currentTimeMillis();
        Throwable failureCause = null;
    
        // 构建语言环境
        LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
        LocaleContext localeContext = buildLocaleContext(request);
    
        // 从请求中获取参数
        RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
        // 从servlet中构建参数
        ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);
    
        // 构建web异步管理器
        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
        asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());
    
        // 初始化上下文信息
        initContextHolders(request, localeContext, requestAttributes);
    
        try {
        
            // 决定一个请求过来应该找到哪个Controller
            doService(request, response);
        }
        catch (ServletException | IOException ex) {
        
            failureCause = ex;
            throw ex;
        }
        catch (Throwable ex) {
        
            failureCause = ex;
            throw new NestedServletException("Request processing failed", ex);
        }
    
        finally {
        
            resetContextHolders(request, previousLocaleContext, previousAttributes);
            if (requestAttributes != null) {
        
                requestAttributes.requestCompleted();
            }
            logResult(request, response, failureCause, asyncManager);
            publishRequestHandledEvent(request, response, startTime, failureCause);
        }
    }

由于`FrameworkServlet`的`doService()`是一个抽象方法（这样看processRequest()也是用了模板方法设计模式），我们去`DispatcherServlet`中看具体的实现

#### 1）doService() ####

@Override
    protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
        
        logRequest(request);
    
        // request请求添加属性
        ......
    
        // 将请求的跳转信息保存起来（Controller的return是return到一个接口）
        if (this.flashMapManager != null) {
        
            FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
            if (inputFlashMap != null) {
        
                request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
            }
            request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
            request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
        }
    
        try {
        
            /**
             * 真正分发请求的地方
             */
            doDispatch(request, response);
        }
        finally {
        
            if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
        
                // Restore the original attribute snapshot, in case of an include.
                if (attributesSnapshot != null) {
        
                    restoreAttributesAfterInclude(request, attributesSnapshot);
                }
            }
        }
    }

接着进入到`doDispatch(request, response)`方法，看它是怎么分派的？

#### 2）doDispatch() ####

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        
        HttpServletRequest processedRequest = request;
        HandlerExecutionChain mappedHandler = null;
        boolean multipartRequestParsed = false;
    
        // web异步处理管理类
        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
    
        try {
        
            // 定义最后返回的ModelAndView视图
            ModelAndView mv = null;
            Exception dispatchException = null;
    
            try {
        
                // Case1、检查请求是否为上传/下载请求
                processedRequest = checkMultipart(request);
                multipartRequestParsed = (processedRequest != request);
    
                // Case2、从handlerMappings中获取请求对应的处理器执行链HandlerExecutionChain
                mappedHandler = getHandler(processedRequest);
                if (mappedHandler == null) {
        
                    noHandlerFound(processedRequest, response);
                    return;
                }
    
                // Case3、 从handlerAdapters中获取请求的适配器`HandlerAdapter`
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
    
                // Process last-modified header, if supported by the handler.
                String method = request.getMethod();
                boolean isGet = "GET".equals(method);
                if (isGet || "HEAD".equals(method)) {
        
                    long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
        
                        return;
                    }
                }
    
                // 执行HandlerExecutionHandler处理链中拦截器的preHandle()方法，如果返回false，则执行afterCompletion()方法并立即返回
                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
        
                    return;
                }
    
                // Case1--Case3都为准备阶段
                // Case4、真正执行请求适配器HandlerAdapter
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
    
                if (asyncManager.isConcurrentHandlingStarted()) {
        
                    return;
                }
    
                applyDefaultViewName(processedRequest, mv);
                // 执行HandlerExecutionHandler处理链中拦截器的postHandle()方法
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }
            catch (Exception ex) {
        
                dispatchException = ex;
            }
            catch (Throwable err) {
        
                // As of 4.3, we're processing Errors thrown from handler methods as well,
                // making them available for @ExceptionHandler methods and other scenarios.
                dispatchException = new NestedServletException("Handler dispatch failed", err);
            }
            // 对发送结果进行处理
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        }
        catch (Exception ex) {
        
            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
        }
        catch (Throwable err) {
        
            triggerAfterCompletion(processedRequest, response, mappedHandler,
                                   new NestedServletException("Handler processing failed", err));
        }
        finally {
        
            if (asyncManager.isConcurrentHandlingStarted()) {
        
                // Instead of postHandle and afterCompletion
                if (mappedHandler != null) {
        
                    mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
                }
            }
            else {
        
                // Clean up any resources used by a multipart request.
                if (multipartRequestParsed) {
        
                    cleanupMultipart(processedRequest);
                }
            }
        }
    }

**Case1：判断是否为上传/下载请求：**

以普通的GET请求为例，判断出不是上传/下载请求；  
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**Case2: 通过`getHandler()`方法获取请求对应的处理器执行链HandlerExecutionChain；**

#### 3）getHandler() ####

@Nullable
    protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
        
        // 在Spring初始化的时候会加载所有的handlerMappings
        if (this.handlerMappings != null) {
        
            for (HandlerMapping mapping : this.handlerMappings) {
        
                // 获取请求对应的HandlerExecutionChain
                HandlerExecutionChain handler = mapping.getHandler(request);
                if (handler != null) {
        
                    return handler;
                }
            }
        }
        return null;
    }

**1> 获取所有HandlerMapping类型的Bean：**

Spring启动时会加载五个HandlerMapping类型的Bean到IOC容器中，分别为：

1.  requestMappingHandlerMapping，请求处理器
2.  beanNameHandlerMapping
3.  routerFunctionMapping
4.  resourceHandlerMapping
5.  welcomePageHandlerMapping

其中针对HTTP GET、POST普通请求而言，我们主要看requestMappingHandlerMapping，其中包含所有注册的可以处理请求、以及请求和相应类/方法的映射Mapping。  
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**2> 以普通的GET、POST请求为例，通过`requestMappingHandlerMapping`获取请求对应的`HandlerExecutionChain`：**

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##### getHandler()方法是如何获取到具体的HandlerExecutionChain的？ #####

进入到`AbstractHandlerMapping`\# getHandler()方法看具体的获取`HandlerExecutionChain`逻辑;

/**
     * 在AbstractHandlerMapping类中
     */
    @Override
    @Nullable
    public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
        
        // 1、获取请求对应的HandlerMethod
        Object handler = getHandlerInternal(request);
        if (handler == null) {
        
            handler = getDefaultHandler();
        }
        if (handler == null) {
        
            return null;
        }
        // Bean name or resolved handler?
        if (handler instanceof String) {
        
            String handlerName = (String) handler;
            handler = obtainApplicationContext().getBean(handlerName);
        }
    
        // 2、获取请求对应的HandlerExecutionChain（默认添加两个拦截器）
        HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
    
        if (logger.isTraceEnabled()) {
        
            logger.trace("Mapped to " + handler);
        }
        else if (logger.isDebugEnabled() && !request.getDispatcherType().equals(DispatcherType.ASYNC)) {
        
            logger.debug("Mapped to " + executionChain.getHandler());
        }
    
        if (hasCorsConfigurationSource(handler) || CorsUtils.isPreFlightRequest(request)) {
        
            CorsConfiguration config = (this.corsConfigurationSource != null ? this.corsConfigurationSource.getCorsConfiguration(request) : null);
            CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
            config = (config != null ? config.combine(handlerConfig) : handlerConfig);
            executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
        }
    
        return executionChain;
    }

**1> 获取请求对应的HandlerMethod:**

/**
     * AbstractHandlerMethodMapping#getHandlerInternal()方法
     */
    @Override
    protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
        
        // 从请求中获取请求的路径
        String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
        request.setAttribute(LOOKUP_PATH, lookupPath);
        this.mappingRegistry.acquireReadLock();
        try {
        
            // 根据请求路径查找相应的HandlerMethod
            HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
            return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
        }
        finally {
        
            this.mappingRegistry.releaseReadLock();
        }
    }

先从请求中获取请求的路径，然后根据请求路径和请求通过`lookupHandlerMethod()`方法获取`HandlerMathod`；

@Nullable
    protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
        
        List<Match> matches = new ArrayList<>();
        // 从mappingRegistry的urlLookup中根据urlPath获取匹配的请求路径
        List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
        if (directPathMatches != null) {
        
            // 找到匹配的请求路径，则添加到matches集合中
            addMatchingMappings(directPathMatches, matches, request);
        }
        if (matches.isEmpty()) {
        
            // No choice but to go through all mappings...
            addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
        }
    
        if (!matches.isEmpty()) {
        
            Match bestMatch = matches.get(0);
            if (matches.size() > 1) {
        
                Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
                matches.sort(comparator);
                bestMatch = matches.get(0);
                if (logger.isTraceEnabled()) {
        
                    logger.trace(matches.size() + " matching mappings: " + matches);
                }
                if (CorsUtils.isPreFlightRequest(request)) {
        
                    return PREFLIGHT_AMBIGUOUS_MATCH;
                }
                Match secondBestMatch = matches.get(1);
                if (comparator.compare(bestMatch, secondBestMatch) == 0) {
        
                    Method m1 = bestMatch.handlerMethod.getMethod();
                    Method m2 = secondBestMatch.handlerMethod.getMethod();
                    String uri = request.getRequestURI();
                    throw new IllegalStateException(
                        "Ambiguous handler methods mapped for '" + uri + "': {" + m1 + ", " + m2 + "}");
                }
            }
            request.setAttribute(BEST_MATCHING_HANDLER_ATTRIBUTE, bestMatch.handlerMethod);
            handleMatch(bestMatch.mapping, lookupPath, request);
            return bestMatch.handlerMethod;
        }
        else {
        
            return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
        }
    }

**phase1**：从mappingRegistry的urlLookup中根据urlPath获取匹配的请求路径（`this.mappingRegistry.getMappingsByUrl(lookupPath)`）：

public List<T> getMappingsByUrl(String urlPath) {
        
        return this.urlLookup.get(urlPath);
    }

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**phase2**：如果获取到多个HandlerMethod，从所有匹配的HandlerMethod中找出一个最匹配的（bestMatch）

**2> 获取请求对应的执行链`HandlerExecutionChain`（默认添加两个拦截器）：**

也就是添加一些拦截器对请求执行过滤、拦截。

protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
        
        HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
                                       (HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
    
        String lookupPath = this.urlPathHelper.getLookupPathForRequest(request, LOOKUP_PATH);
        for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
        
            if (interceptor instanceof MappedInterceptor) {
        
                MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
                if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
        
                    chain.addInterceptor(mappedInterceptor.getInterceptor());
                }
            }
            else {
        
                chain.addInterceptor(interceptor);
            }
        }
        return chain;
    }

其中默认添加两个拦截器：

1.  ConversionServiceExposingInterceptor
2.  ResourceUrlProviderExposingInterceptor

**我们项目中自定义的`HandlerInterceptor`也会被加入到HandlerExecutionChain。**

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**Case3: 获取完请求对应的`HandlerExecutionChain`之后，通过`getHandlerAdapter()`进一步获取请求的适配器`HandlerAdapter`；**

#### 4）getHandlerAdapter() ####

对于HTTP请求而言，HandlerAdapter就是`HttpRequestHandlerAdapter`；

protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
        
        if (this.handlerAdapters != null) {
        
            // 1、获取所有HandlerAdapter类型的bean
            for (HandlerAdapter adapter : this.handlerAdapters) {
        
                // 找到具体HandlerAdapter
                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");
    }

**1> 获取所有HandlerAdapter类型的Bean：**

Spring启动时会加载四个HandlerAdapter类型的Bean到IOC容器中，分别为：

1.  RequestMappingHandlerAdapter，HTTP请求的HandlerAdapter
2.  HandlerFunctionAdapter
3.  HttpRequestHandlerAdapter
4.  SimpleControllerHandlerAdapter

**2> 找到符合相应HandlerMethod的HandlerAdapter：**

HandlerAdapter\#supports()方法本质上就是一个`instanceof`类型判断，以`HttpRequestHandlerAdapter`为例：

public class HttpRequestHandlerAdapter implements HandlerAdapter {
        
    
    	@Override
    	public boolean supports(Object handler) {
        
    		return (handler instanceof HttpRequestHandler);
    	}    
        .....
    }

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**Case4: 通过HandlerAdapter\#handle()方法开始真正执行相应的`HandlerAdapter`;**

#### 5）HandlerAdapter\#handle() ####

进入到`AbstractHandlerMethodAdapter#handle()`方法

@Override
    @Nullable
    public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
        throws Exception {
        
    
        return handleInternal(request, response, (HandlerMethod) handler);
    }

这里`AbstractHandlerMethodAdapter#handleInternal()`又是一个抽象方法，即其上层`handle()`方法是一个模板方法

@Nullable
    protected abstract ModelAndView handleInternal(HttpServletRequest request,
                                                   HttpServletResponse response, HandlerMethod handlerMethod) throws Exception;

对于HTTP请求，会进入到`AbstractHandlerMethodAdapter`的子类`RequestHandlerMethodAdapter`\#handlerInternal()方法：

@Override
    protected ModelAndView handleInternal(HttpServletRequest request,
                                          HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
        
    
        ModelAndView mav;
        checkRequest(request);
    
        // Execute invokeHandlerMethod in synchronized block if required.
        if (this.synchronizeOnSession) {
        
            HttpSession session = request.getSession(false);
            if (session != null) {
        
                Object mutex = WebUtils.getSessionMutex(session);
                synchronized (mutex) {
        
                    mav = invokeHandlerMethod(request, response, handlerMethod);
                }
            }
            else {
        
                // No HttpSession available -> no mutex necessary
                mav = invokeHandlerMethod(request, response, handlerMethod);
            }
        }
        else {
        
            // 真正执行适配器adapter的方法
            // No synchronization on session demanded at all...
            mav = invokeHandlerMethod(request, response, handlerMethod);
        }
    
        if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
        
            if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
        
                applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
            }
            else {
        
                prepareResponse(response);
            }
        }
    
        return mav;
    }

进入到`invokeHandlerMethod()`方法，看看Spring MVC是如何执行适配器HandlerAdapter的方法的？

#### 6）RequestHandlerMethodAdapter\#invokeHandlerMethod() ####

@Nullable
    protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
                                               HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
        
    
        ServletWebRequest webRequest = new ServletWebRequest(request, response);
        try {
        
            WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
            ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
    
            ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
            // 解析请求的参数，参数解析器HandlerMethodArgumentResolverComposite有26个
            if (this.argumentResolvers != null) {
        
                invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
            }
            // 返回值处理器
            if (this.returnValueHandlers != null) {
        
                invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
            }
            // 一堆赋值操作
            .....
    
            // 调用方法，然后执行
            invocableMethod.invokeAndHandle(webRequest, mavContainer);
            if (asyncManager.isConcurrentHandlingStarted()) {
        
                return null;
            }
    
            return getModelAndView(mavContainer, modelFactory, webRequest);
        }
        finally {
        
            webRequest.requestCompleted();
        }
    }

**phase1：获取参数解析器HandlerMethodArgumentResolver；**

**参数解析器`HandlerMethodArgumentResolver`**

*  包含两个方法，分别为
 *  **supportsParameter()** —> 判断响应方法参数parameter是否可以被当前HandlerMethodArgumentResolver解析？
 *  **resolveArgument()** —> 进行方法参数解析

public interface HandlerMethodArgumentResolver {
        
        // 判断parameter是不是xxArgumentResolver可以解析的
        boolean supportsParameter(MethodParameter parameter);
    
        @Nullable
        // 方法参数解析的主要逻辑
        @Nullable
        Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
                               NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception;
    }

*  方法参数解析器argumentResolvers一共有26个：  
    ![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA56eD5aS054ix5YGl6Lqr_size_20_color_FFFFFF_t_70_g_se_x_16 3]  
    ![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA56eD5aS054ix5YGl6Lqr_size_20_color_FFFFFF_t_70_g_se_x_16 4]

> 0 = \{RequestParamMethodArgumentResolver@6374\}  
> 1 = \{RequestParamMapMethodArgumentResolver@6375\}  
> 2 = \{PathVariableMethodArgumentResolver@6376\}  
> 3 = \{PathVariableMapMethodArgumentResolver@6377\}  
> 4 = \{MatrixVariableMethodArgumentResolver@6378\}  
> 5 = \{MatrixVariableMapMethodArgumentResolver@6379\}  
> 6 = \{ServletModelAttributeMethodProcessor@6380\}  
> 7 = \{RequestResponseBodyMethodProcessor@6381\}  
> 8 = \{RequestPartMethodArgumentResolver@6382\}  
> 9 = \{RequestHeaderMethodArgumentResolver@6383\}  
> 10 = \{RequestHeaderMapMethodArgumentResolver@6384\}  
> 11 = \{ServletCookieValueMethodArgumentResolver@6385\}  
> 12 = \{ExpressionValueMethodArgumentResolver@6386\}  
> 13 = \{SessionAttributeMethodArgumentResolver@6387\}  
> 14 = \{RequestAttributeMethodArgumentResolver@6388\}  
> 15 = \{ServletRequestMethodArgumentResolver@6389\}  
> 16 = \{ServletResponseMethodArgumentResolver@6390\}  
> 17 = \{HttpEntityMethodProcessor@6391\}  
> 18 = \{RedirectAttributesMethodArgumentResolver@6392\}  
> 19 = \{ModelMethodProcessor@6393\}  
> 20 = \{MapMethodProcessor@6394\}  
> 21 = \{ErrorsMethodArgumentResolver@6395\}  
> 22 = \{SessionStatusMethodArgumentResolver@6396\}  
> 23 = \{UriComponentsBuilderMethodArgumentResolver@6397\}  
> 24 = \{RequestParamMethodArgumentResolver@6398\}  
> 25 = \{ServletModelAttributeMethodProcessor@6399\}

**phase2：获取返回值/结果处理器HandlerMethodReturnValueHandler；**

**返回值/结果处理器`HandlerMethodReturnValueHandler`**

*  包含两个方法，分别为
 *  **supportsReturnType()** —> 判断响应方法放回值是否可以被当前HandlerMethodReturnValueHandler处理？
 *  **handleReturnValue()** —> 进行返回值处理

public interface HandlerMethodReturnValueHandler {
        
        //xxMethodReturnValueHandler是否能处理这个returnType
        boolean supportsReturnType(MethodParameter returnType);
    
        // 处理返回值
        void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
                               ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception;

*  返回值/结果处理器一共有15个：  
    ![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA56eD5aS054ix5YGl6Lqr_size_20_color_FFFFFF_t_70_g_se_x_16 5]  
    ![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA56eD5aS054ix5YGl6Lqr_size_20_color_FFFFFF_t_70_g_se_x_16 6]

> 0 = \{ModelAndViewMethodReturnValueHandler@6417\}  
> 1 = \{ModelMethodProcessor@6418\}  
> 2 = \{ViewMethodReturnValueHandler@6419\}  
> 3 = \{ResponseBodyEmitterReturnValueHandler@6420\}  
> 4 = \{StreamingResponseBodyReturnValueHandler@6421\}  
> 5 = \{HttpEntityMethodProcessor@6422\}  
> 6 = \{HttpHeadersReturnValueHandler@6423\}  
> 7 = \{CallableMethodReturnValueHandler@6424\}  
> 8 = \{DeferredResultMethodReturnValueHandler@6425\}  
> 9 = \{AsyncTaskMethodReturnValueHandler@6426\}  
> 10 = \{ModelAttributeMethodProcessor@6427\}  
> 11 = \{RequestResponseBodyMethodProcessor@6428\}  
> 12 = \{ViewNameMethodReturnValueHandler@6429\}  
> 13 = \{MapMethodProcessor@6430\}

**phase3：执行方法；**

进入到`ServletInvocableHandlerMethod`\#`invokeAndHandle(webRequest, mavContainer)`方法；

public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
                                Object... providedArgs) throws Exception {
        
    
        // 真正执行请求的地方
        Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
        // 下面全部为处理返回结果
        setResponseStatus(webRequest);
    
        if (returnValue == null) {
        
            if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
        
                disableContentCachingIfNecessary(webRequest);
                mavContainer.setRequestHandled(true);
                return;
            }
        }
        else if (StringUtils.hasText(getResponseStatusReason())) {
        
            mavContainer.setRequestHandled(true);
            return;
        }
    
        mavContainer.setRequestHandled(false);
        Assert.state(this.returnValueHandlers != null, "No return value handlers");
        try {
        
            this.returnValueHandlers.handleReturnValue(
                returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
        }
        catch (Exception ex) {
        
            if (logger.isTraceEnabled()) {
        
                logger.trace(formatErrorForReturnValue(returnValue), ex);
            }
            throw ex;
        }
    }

**再进入到`InvocableHandlerMethod`\#`invokeForRequest()`看是如何处理请求的？**

@Nullable
    public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
                                   Object... providedArgs) throws Exception {
        
    
        // 获取方法的入参
        Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
        if (logger.isTraceEnabled()) {
        
            logger.trace("Arguments: " + Arrays.toString(args));
        }
        // 调用真正的Controller
        return doInvoke(args);
    }

再看`doInvoke()`方法如何执行？

*  通过反射、打开Controller相应方法的访问权限，进而调用相应的方法。

@Nullable
    protected Object doInvoke(Object... args) throws Exception {
        
        // 获得被桥接的⽅法（如果是桥接方法，则返回被桥接的方法，否则直接返回 getMethod()），然后打开访问权限
        ReflectionUtils.makeAccessible(getBridgedMethod());
        try {
        
            //  通过反射，调⽤Controller中相应的⽅法
            return getBridgedMethod().invoke(getBean(), args);
        }
        catch (IllegalArgumentException ex) {
        
            ......
        }
    }

**最后再回到DispatcherServlet\#doDispatch()方法中，看其调用processDispatchResult()方法如何处理返回结果？**

#### processDispatchResult() ####

这里会进行异常的处理、视图的渲染、以及HandlerAdapter中所有拦截器的afterCompletion()方法。

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
    		@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
    		@Nullable Exception exception) throws Exception {
        
    
    	boolean errorView = false;
    
    	/** 如果发生了异常，对异常进行处理 */
    	if (exception != null) {
        
    		if (exception instanceof ModelAndViewDefiningException) {
        
    			logger.debug("ModelAndViewDefiningException encountered", exception);
    			mv = ((ModelAndViewDefiningException) exception).getModelAndView();
    		}
    		else {
        
    			Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
    			mv = processHandlerException(request, response, handler, exception);
    			errorView = (mv != null);
    		}
    	}
    
    	/** 处理程序是否返回要渲染的视图？ */
    	if (mv != null && !mv.wasCleared()) {
        
    		/** 进行视图渲染 */
    		// eg3:
    		render(mv, request, response);
    		if (errorView) {
        
    			WebUtils.clearErrorRequestAttributes(request);
    		}
    	}
    	else {
        
    		if (logger.isTraceEnabled()) {
        
    			logger.trace("No view rendering, null ModelAndView returned.");
    		}
    	}
    
    	if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
        
    		// Concurrent handling started during a forward
    		return;
    	}
    
        // 执行HandlerExecutionChain中拦截器的afterCompletion()方法
    	if (mappedHandler != null) {
        
    		mappedHandler.triggerAfterCompletion(request, response, null);
    	}
    }

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