spring源码学习之springMVC（二）

 1 @Override
 2 protected final void doGet(HttpServletRequest request, HttpServletResponse response)
 3         throws ServletException, IOException {
 4 
 5     processRequest(request, response);
 6 }
 7 
 8 @Override
 9 protected final void doPost(HttpServletRequest request, HttpServletResponse response)
10         throws ServletException, IOException {
11 
12     processRequest(request, response);
13 }
14 
15 // 对于不同的方法，spring并没有做特殊处理，而是统一将程序再一次地引导至processRequest(request, response);中
16 org.springframework.web.servlet.FrameworkServlet类中
17 protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
18         throws ServletException, IOException {
19 
20     // 记录当前时间，用于计算web请求的处理时间
21     long startTime = System.currentTimeMillis();
22     Throwable failureCause = null;
23 
24     LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
25     LocaleContext localeContext = buildLocaleContext(request);
26 
27     RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
28     ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);
29 
30     WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
31     asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());
32 
33     initContextHolders(request, localeContext, requestAttributes);
34 
35     try {
36         doService(request, response);
37     }
38     catch (ServletException | IOException ex) {
39         failureCause = ex;
40         throw ex;
41     }
42     catch (Throwable ex) {
43         failureCause = ex;
44         throw new NestedServletException("Request processing failed", ex);
45     }
46 
47     finally {
48         resetContextHolders(request, previousLocaleContext, previousAttributes);
49         if (requestAttributes != null) {
50             requestAttributes.requestCompleted();
51         }
52 
53         if (logger.isDebugEnabled()) {
54             if (failureCause != null) {
55                 this.logger.debug("Could not complete request", failureCause);
56             }
57             else {
58                 if (asyncManager.isConcurrentHandlingStarted()) {
59                     logger.debug("Leaving response open for concurrent processing");
60                 }
61                 else {
62                     this.logger.debug("Successfully completed request");
63                 }
64             }
65         }
66 
67         publishRequestHandledEvent(request, response, startTime, failureCause);
68     }
69 }

 1 @Override
 2 protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
 3     if (logger.isDebugEnabled()) {
 4         String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
 5         logger.debug("DispatcherServlet with name ‘" + getServletName() + "‘" + resumed +
 6                 " processing " + request.getMethod() + " request for [" + getRequestUri(request) + "]");
 7     }
 8 
 9     // Keep a snapshot of the request attributes in case of an include,
10     // to be able to restore the original attributes after the include.
11     Map<String, Object> attributesSnapshot = null;
12     if (WebUtils.isIncludeRequest(request)) {
13         attributesSnapshot = new HashMap<>();
14         Enumeration<?> attrNames = request.getAttributeNames();
15         while (attrNames.hasMoreElements()) {
16             String attrName = (String) attrNames.nextElement();
17             if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
18                 attributesSnapshot.put(attrName, request.getAttribute(attrName));
19             }
20         }
21     }
22 
23     // Make framework objects available to handlers and view objects.
24     request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
25     request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
26     request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
27     request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());
28 
29     if (this.flashMapManager != null) {
30         FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
31         if (inputFlashMap != null) {
32             request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
33         }
34         request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
35         request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
36     }
37 
38     try {
39         doDispatch(request, response);
40     }
41     finally {
42         if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
43             // Restore the original attribute snapshot, in case of an include.
44             if (attributesSnapshot != null) {
45                 restoreAttributesAfterInclude(request, attributesSnapshot);
46             }
47         }
48     }
49 }

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    HttpServletRequest processedRequest = request;
    HandlerExecutionChain mappedHandler = null;
    boolean multipartRequestParsed = false;

    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

    try {
        ModelAndView mv = null;
        Exception dispatchException = null;

        try {
            // 如果是MultipartContext类型的request则转换request为MultipartHttpServletRequest类型的
            processedRequest = checkMultipart(request);
            multipartRequestParsed = (processedRequest != request);

            // Determine handler for the current request.
            // 根据request信息寻找对应的handler
            mappedHandler = getHandler(processedRequest);
            if (mappedHandler == null) {
                // 如果没有找到handler，则通过response反馈错误信息
                noHandlerFound(processedRequest, response);
                return;
            }

            // Determine handler adapter for the current request.
            // 根据当前的Handler寻找对应的HandlerAdapter
            HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

            // Process last-modified header, if supported by the handler.
            // 如果当前handler支持last-modified头处理
            String method = request.getMethod();
            boolean isGet = "GET".equals(method);
            if (isGet || "HEAD".equals(method)) {
                long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                if (logger.isDebugEnabled()) {
                    logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
                }
                if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                    return;
                }
            }

            // 拦截器的preHandler方法的调用
            if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                return;
            }

            // Actually invoke the handler.
            // 真正的激活Handler并返回视图
            mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

            if (asyncManager.isConcurrentHandlingStarted()) {
                return;
            }

            // 视图名称转换应用于需要添加前缀后缀的情况
            applyDefaultViewName(processedRequest, mv);
            // 应用所有拦截器的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);
        }
        // 处理异常视图，根据视图来跳转页面
        processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
    }
    catch (Exception ex) {
        // 完成处理激活触发器
        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);
            }
        }
    }
}

// doDispatch方法中展示了spring请求处理所涉及的主要逻辑，下面是逻辑处理全过程的详细分析：

 1 protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
 2     if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) {
 3         if (WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class) != null) {
 4             logger.debug("Request is already a MultipartHttpServletRequest - if not in a forward, " +
 5                     "this typically results from an additional MultipartFilter in web.xml");
 6         }
 7         else if (hasMultipartException(request)) {
 8             logger.debug("Multipart resolution previously failed for current request - " +
 9                     "skipping re-resolution for undisturbed error rendering");
10         }
11         else {
12             try {
13                 return this.multipartResolver.resolveMultipart(request);
14             }
15             catch (MultipartException ex) {
16                 if (request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) != null) {
17                     logger.debug("Multipart resolution failed for error dispatch", ex);
18                     // Keep processing error dispatch with regular request handle below
19                 }
20                 else {
21                     throw ex;
22                 }
23             }
24         }
25     }
26     // If not returned before: return original request.
27     return request;
28 }

1 <bean id="simpleUrlHandlerMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
2     <property name="mappings">
3         <props>
4             <prop key="/userlist.htm">userController</prop>
5         </props>
6     </property>
7 </bean>

 1 @Nullable
 2 protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
 3     if (this.handlerMappings != null) {
 4         for (HandlerMapping hm : this.handlerMappings) {
 5             if (logger.isTraceEnabled()) {
 6                 logger.trace(
 7                         "Testing handler map [" + hm + "] in DispatcherServlet with name ‘" + getServletName() + "‘");
 8             }
 9             HandlerExecutionChain handler = hm.getHandler(request);
10             if (handler != null) {
11                 return handler;
12             }
13         }
14     }
15     return null;
16 }

 1 @Override
 2 @Nullable
 3 public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
 4     // 根据request获取对应的Handler
 5     Object handler = getHandlerInternal(request);
 6     if (handler == null) {
 7         // 如果没有找到对应的handler 则使用默认的
 8         handler = getDefaultHandler();
 9     }
10     if (handler == null) {
11         // 默认的也没有，则返回null
12         return null;
13     }
14     // Bean name or resolved handler?
15     if (handler instanceof String) {
16         String handlerName = (String) handler;
17         handler = obtainApplicationContext().getBean(handlerName);
18     }
19     // 加入拦截器到执行链
20     HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
21     if (CorsUtils.isCorsRequest(request)) {
22         CorsConfiguration globalConfig = this.globalCorsConfigSource.getCorsConfiguration(request);
23         CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
24         CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
25         executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
26     }
27     return executionChain;
28 }

  1 @Override
  2 @Nullable
  3 protected Object getHandlerInternal(HttpServletRequest request) throws Exception {
  4     // 截取用于匹配的URL路径
  5     String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
  6     // 根据路径寻找handler
  7     Object handler = lookupHandler(lookupPath, request);
  8     if (handler == null) {
  9         // We need to care for the default handler directly, since we need to
 10         // expose the PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE for it as well.
 11         Object rawHandler = null;
 12         if ("/".equals(lookupPath)) {
 13             // 如果请求的路径仅仅是"/"，那么使用RootHandler处理
 14             rawHandler = getRootHandler();
 15         }
 16         if (rawHandler == null) {
 17             // 无法使用handler 则使用默认的handler
 18             rawHandler = getDefaultHandler();
 19         }
 20         if (rawHandler != null) {
 21             // Bean name or resolved handler?
 22             if (rawHandler instanceof String) {
 23                 // 根据beanName获取对应的bean
 24                 String handlerName = (String) rawHandler;
 25                 rawHandler = obtainApplicationContext().getBean(handlerName);
 26             }
 27             validateHandler(rawHandler, request);
 28             // 模板方法
 29             handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null);
 30         }
 31     }
 32     if (handler != null && logger.isDebugEnabled()) {
 33         logger.debug("Mapping [" + lookupPath + "] to " + handler);
 34     }
 35     else if (handler == null && logger.isTraceEnabled()) {
 36         logger.trace("No handler mapping found for [" + lookupPath + "]");
 37     }
 38     return handler;
 39 }
 40 
 41 @Nullable
 42 protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {
 43     // Direct match?
 44     // 直接匹配的情况处理
 45     Object handler = this.handlerMap.get(urlPath);
 46     if (handler != null) {
 47         // Bean name or resolved handler?
 48         if (handler instanceof String) {
 49             String handlerName = (String) handler;
 50             handler = obtainApplicationContext().getBean(handlerName);
 51         }
 52         validateHandler(handler, request);
 53         return buildPathExposingHandler(handler, urlPath, urlPath, null);
 54     }
 55 
 56     // Pattern match?
 57     // 通配符匹配的处理
 58     List<String> matchingPatterns = new ArrayList<>();
 59     for (String registeredPattern : this.handlerMap.keySet()) {
 60         if (getPathMatcher().match(registeredPattern, urlPath)) {
 61             matchingPatterns.add(registeredPattern);
 62         }
 63         else if (useTrailingSlashMatch()) {
 64             if (!registeredPattern.endsWith("/") && getPathMatcher().match(registeredPattern + "/", urlPath)) {
 65                 matchingPatterns.add(registeredPattern + "/");
 66             }
 67         }
 68     }
 69 
 70     String bestMatch = null;
 71     Comparator<String> patternComparator = getPathMatcher().getPatternComparator(urlPath);
 72     if (!matchingPatterns.isEmpty()) {
 73         matchingPatterns.sort(patternComparator);
 74         if (logger.isDebugEnabled()) {
 75             logger.debug("Matching patterns for request [" + urlPath + "] are " + matchingPatterns);
 76         }
 77         bestMatch = matchingPatterns.get(0);
 78     }
 79     if (bestMatch != null) {
 80         handler = this.handlerMap.get(bestMatch);
 81         if (handler == null) {
 82             if (bestMatch.endsWith("/")) {
 83                 handler = this.handlerMap.get(bestMatch.substring(0, bestMatch.length() - 1));
 84             }
 85             if (handler == null) {
 86                 throw new IllegalStateException(
 87                         "Could not find handler for best pattern match [" + bestMatch + "]");
 88             }
 89         }
 90         // Bean name or resolved handler?
 91         if (handler instanceof String) {
 92             String handlerName = (String) handler;
 93             handler = obtainApplicationContext().getBean(handlerName);
 94         }
 95         validateHandler(handler, request);
 96         String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestMatch, urlPath);
 97 
 98         // There might be multiple ‘best patterns‘, let‘s make sure we have the correct URI template variables
 99         // for all of them
100         Map<String, String> uriTemplateVariables = new LinkedHashMap<>();
101         for (String matchingPattern : matchingPatterns) {
102             if (patternComparator.compare(bestMatch, matchingPattern) == 0) {
103                 Map<String, String> vars = getPathMatcher().extractUriTemplateVariables(matchingPattern, urlPath);
104                 Map<String, String> decodedVars = getUrlPathHelper().decodePathVariables(request, vars);
105                 uriTemplateVariables.putAll(decodedVars);
106             }
107         }
108         if (logger.isDebugEnabled()) {
109             logger.debug("URI Template variables for request [" + urlPath + "] are " + uriTemplateVariables);
110         }
111         return buildPathExposingHandler(handler, bestMatch, pathWithinMapping, uriTemplateVariables);
112     }
113 
114     // No handler found...
115     return null;
116 }
117 
118 // 根据URL获取对应的Handler的匹配规则代码实现起来虽然很长，但是并不难理解，考虑了直接匹配与通配符两种情况，其中提及的是buildPathExposingHandler，
119 // 他将Handler封装成HandlerExecutionChain类型
120 
121 protected Object buildPathExposingHandler(Object rawHandler, String bestMatchingPattern,
122         String pathWithinMapping, @Nullable Map<String, String> uriTemplateVariables) {
123 
124     HandlerExecutionChain chain = new HandlerExecutionChain(rawHandler);
125     chain.addInterceptor(new PathExposingHandlerInterceptor(bestMatchingPattern, pathWithinMapping));
126     if (!CollectionUtils.isEmpty(uriTemplateVariables)) {
127         chain.addInterceptor(new UriTemplateVariablesHandlerInterceptor(uriTemplateVariables));
128     }
129     return chain;
130 }

 1 protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
 2     HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
 3             (HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
 4 
 5     String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
 6     for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
 7         if (interceptor instanceof MappedInterceptor) {
 8             MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
 9             if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
10                 chain.addInterceptor(mappedInterceptor.getInterceptor());
11             }
12         }
13         else {
14             chain.addInterceptor(interceptor);
15         }
16     }
17     return chain;
18 }

 1 protected void noHandlerFound(HttpServletRequest request, HttpServletResponse response) throws Exception {
 2     if (pageNotFoundLogger.isWarnEnabled()) {
 3         pageNotFoundLogger.warn("No mapping found for HTTP request with URI [" + getRequestUri(request) +
 4                 "] in DispatcherServlet with name ‘" + getServletName() + "‘");
 5     }
 6     if (this.throwExceptionIfNoHandlerFound) {
 7         throw new NoHandlerFoundException(request.getMethod(), getRequestUri(request),
 8                 new ServletServerHttpRequest(request).getHeaders());
 9     }
10     else {
11         response.sendError(HttpServletResponse.SC_NOT_FOUND);
12     }
13 }

protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
    if (this.handlerAdapters != null) {
        for (HandlerAdapter ha : this.handlerAdapters) {
            if (logger.isTraceEnabled()) {
                logger.trace("Testing handler adapter [" + ha + "]");
            }
            if (ha.supports(handler)) {
                return ha;
            }
        }
    }
    throw new ServletException("No adapter for handler [" + handler +
            "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}

// 通过上面的函数，无非就是遍历所有的适配器来选择合适的适配器并返回它，而某个适配器是否适用于当前的Handler逻辑被封装在具体的适配器中，进一步查看SimpleControllerHandlerAdapter类中的supports方法

@Override
public boolean supports(Object handler) {
    return (handler instanceof Controller);
}

// 分析到这里的话，SimpleControllerHandlerAdapter就是用来处理普通的web请求的，而且对于springMVC来说，我们会把逻辑封装在Controller的子类中，也就是开发人员自己定义的Controller类

 1 @Override
 2 @Nullable
 3 public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
 4         throws Exception {
 5 
 6     return ((Controller) handler).handleRequest(request, response);
 7 }
 8 
 9 org.springframework.web.servlet.mvc.AbstractController中
10 @Override
11 @Nullable
12 public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response)
13         throws Exception {
14 
15     if (HttpMethod.OPTIONS.matches(request.getMethod())) {
16         response.setHeader("Allow", getAllowHeader());
17         return null;
18     }
19 
20     // Delegate to WebContentGenerator for checking and preparing.
21     checkRequest(request);
22     prepareResponse(response);
23 
24     // Execute handleRequestInternal in synchronized block if required.
25     // 如果需要session内的同步执行
26     if (this.synchronizeOnSession) {
27         HttpSession session = request.getSession(false);
28         if (session != null) {
29             Object mutex = WebUtils.getSessionMutex(session);
30             synchronized (mutex) {
31                 // 调用客户的逻辑
32                 return handleRequestInternal(request, response);
33             }
34         }
35     }
36 
37     // 调用客户的逻辑
38     return handleRequestInternal(request, response);
39 }

 1 // processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
 2 
 3 private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
 4         @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
 5         @Nullable Exception exception) throws Exception {
 6 
 7     boolean errorView = false;
 8 
 9     if (exception != null) {
10         if (exception instanceof ModelAndViewDefiningException) {
11             logger.debug("ModelAndViewDefiningException encountered", exception);
12             mv = ((ModelAndViewDefiningException) exception).getModelAndView();
13         }
14         else {
15             Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
16             mv = processHandlerException(request, response, handler, exception);
17             errorView = (mv != null);
18         }
19     }
20 
21     // Did the handler return a view to render?
22     if (mv != null && !mv.wasCleared()) {
23         // 根据视图页面
24         render(mv, request, response);
25         if (errorView) {
26             WebUtils.clearErrorRequestAttributes(request);
27         }
28     }
29     else {
30         if (logger.isDebugEnabled()) {
31             logger.debug("Null ModelAndView returned to DispatcherServlet with name ‘" + getServletName() +
32                     "‘: assuming HandlerAdapter completed request handling");
33         }
34     }
35 
36     if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
37         // Concurrent handling started during a forward
38         return;
39     }
40 
41     if (mappedHandler != null) {
42         mappedHandler.triggerAfterCompletion(request, response, null);
43     }
44 }
45 
46 // processHandlerException方法中异常视图的处理
47 @Nullable
48 protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
49         @Nullable Object handler, Exception ex) throws Exception {
50 
51     // Check registered HandlerExceptionResolvers...
52     ModelAndView exMv = null;
53     if (this.handlerExceptionResolvers != null) {
54         for (HandlerExceptionResolver handlerExceptionResolver : this.handlerExceptionResolvers) {
55             exMv = handlerExceptionResolver.resolveException(request, response, handler, ex);
56             if (exMv != null) {
57                 break;
58             }
59         }
60     }
61     if (exMv != null) {
62         if (exMv.isEmpty()) {
63             request.setAttribute(EXCEPTION_ATTRIBUTE, ex);
64             return null;
65         }
66         // We might still need view name translation for a plain error model...
67         if (!exMv.hasView()) {
68             String defaultViewName = getDefaultViewName(request);
69             if (defaultViewName != null) {
70                 exMv.setViewName(defaultViewName);
71             }
72         }
73         if (logger.isDebugEnabled()) {
74             logger.debug("Handler execution resulted in exception - forwarding to resolved error view: " + exMv, ex);
75         }
76         WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());
77         return exMv;
78     }
79 
80     throw ex;
81 }

 1 protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
 2     // Determine locale for request and apply it to the response.
 3     Locale locale =
 4             (this.localeResolver != null ? this.localeResolver.resolveLocale(request) : request.getLocale());
 5     response.setLocale(locale);
 6 
 7     View view;
 8     String viewName = mv.getViewName();
 9     if (viewName != null) {
10         // We need to resolve the view name.
11         // 解析视图名称
12         view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
13         if (view == null) {
14             throw new ServletException("Could not resolve view with name ‘" + mv.getViewName() +
15                     "‘ in servlet with name ‘" + getServletName() + "‘");
16         }
17     }
18     else {
19         // No need to lookup: the ModelAndView object contains the actual View object.
20         view = mv.getView();
21         if (view == null) {
22             throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +
23                     "View object in servlet with name ‘" + getServletName() + "‘");
24         }
25     }
26 
27     // Delegate to the View object for rendering.
28     if (logger.isDebugEnabled()) {
29         logger.debug("Rendering view [" + view + "] in DispatcherServlet with name ‘" + getServletName() + "‘");
30     }
31     try {
32         if (mv.getStatus() != null) {
33             response.setStatus(mv.getStatus().value());
34         }
35         // 页面跳转
36         view.render(mv.getModelInternal(), request, response);
37     }
38     catch (Exception ex) {
39         if (logger.isDebugEnabled()) {
40             logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name ‘" +
41                     getServletName() + "‘", ex);
42         }
43         throw ex;
44     }
45 }

  1 protected View resolveViewName(String viewName, @Nullable Map<String, Object> model,
  2         Locale locale, HttpServletRequest request) throws Exception {
  3 
  4     if (this.viewResolvers != null) {
  5         for (ViewResolver viewResolver : this.viewResolvers) {
  6             View view = viewResolver.resolveViewName(viewName, locale);
  7             if (view != null) {
  8                 return view;
  9             }
 10         }
 11     }
 12     return null;
 13 }
 14 // 我们以org.springframework.web.servlet.view.AbstractCachingViewResolver.resolveViewName(String, Locale)为例子分析ViewResolver逻辑的解析过程，
 15 
 16 @Override
 17 @Nullable
 18 public View resolveViewName(String viewName, Locale locale) throws Exception {
 19     if (!isCache()) {
 20         // 不存在缓存的情况下直接
 21         return createView(viewName, locale);
 22     }
 23     else {
 24         // 直接从缓存中提取
 25         Object cacheKey = getCacheKey(viewName, locale);
 26         View view = this.viewAccessCache.get(cacheKey);
 27         if (view == null) {
 28             synchronized (this.viewCreationCache) {
 29                 view = this.viewCreationCache.get(cacheKey);
 30                 if (view == null) {
 31                     // Ask the subclass to create the View object.
 32                     view = createView(viewName, locale);
 33                     if (view == null && this.cacheUnresolved) {
 34                         view = UNRESOLVED_VIEW;
 35                     }
 36                     if (view != null) {
 37                         this.viewAccessCache.put(cacheKey, view);
 38                         this.viewCreationCache.put(cacheKey, view);
 39                         if (logger.isTraceEnabled()) {
 40                             logger.trace("Cached view [" + cacheKey + "]");
 41                         }
 42                     }
 43                 }
 44             }
 45         }
 46         return (view != UNRESOLVED_VIEW ? view : null);
 47     }
 48 }
 49 
 50 // org.springframework.web.servlet.view.UrlBasedViewResolver中重写的createView方法
 51 @Override
 52 protected View createView(String viewName, Locale locale) throws Exception {
 53     // If this resolver is not supposed to handle the given view,
 54     // return null to pass on to the next resolver in the chain.
 55     // 如果当前解析器不支持当前解析器 如viewName为空
 56     if (!canHandle(viewName, locale)) {
 57         return null;
 58     }
 59 
 60     // Check for special "redirect:" prefix.
 61     // 处理前缀为redirect:x的情况
 62     if (viewName.startsWith(REDIRECT_URL_PREFIX)) {
 63         String redirectUrl = viewName.substring(REDIRECT_URL_PREFIX.length());
 64         RedirectView view = new RedirectView(redirectUrl,
 65                 isRedirectContextRelative(), isRedirectHttp10Compatible());
 66         String[] hosts = getRedirectHosts();
 67         if (hosts != null) {
 68             view.setHosts(hosts);
 69         }
 70         return applyLifecycleMethods(REDIRECT_URL_PREFIX, view);
 71     }
 72 
 73     // Check for special "forward:" prefix.
 74     // 处理前缀为forward:x的情况 
 75     if (viewName.startsWith(FORWARD_URL_PREFIX)) {
 76         String forwardUrl = viewName.substring(FORWARD_URL_PREFIX.length());
 77         return new InternalResourceView(forwardUrl);
 78     }
 79 
 80     // Else fall back to superclass implementation: calling loadView.
 81     return super.createView(viewName, locale);
 82 }
 83 
 84 //org.springframework.web.servlet.view.AbstractCachingViewResolver父类中的createView
 85 @Nullable
 86 protected View createView(String viewName, Locale locale) throws Exception {
 87     return loadView(viewName, locale);
 88 }
 89 
 90 // org.springframework.web.servlet.view.UrlBasedViewResolver子类中重写loadView
 91 @Override
 92 protected View loadView(String viewName, Locale locale) throws Exception {
 93     AbstractUrlBasedView view = buildView(viewName);
 94     View result = applyLifecycleMethods(viewName, view);
 95     return (view.checkResource(locale) ? result : null);
 96 }
 97 
 98 protected AbstractUrlBasedView buildView(String viewName) throws Exception {
 99     Class<?> viewClass = getViewClass();
100     Assert.state(viewClass != null, "No view class");
101 
102     AbstractUrlBasedView view = (AbstractUrlBasedView) BeanUtils.instantiateClass(viewClass);
103     // 添加前缀以及后缀
104     view.setUrl(getPrefix() + viewName + getSuffix());
105 
106     String contentType = getContentType();
107     if (contentType != null) {
108         // 设置ContentType
109         view.setContentType(contentType);
110     }
111 
112     view.setRequestContextAttribute(getRequestContextAttribute());
113     view.setAttributesMap(getAttributesMap());
114 
115     Boolean exposePathVariables = getExposePathVariables();
116     if (exposePathVariables != null) {
117         view.setExposePathVariables(exposePathVariables);
118     }
119     Boolean exposeContextBeansAsAttributes = getExposeContextBeansAsAttributes();
120     if (exposeContextBeansAsAttributes != null) {
121         view.setExposeContextBeansAsAttributes(exposeContextBeansAsAttributes);
122     }
123     String[] exposedContextBeanNames = getExposedContextBeanNames();
124     if (exposedContextBeanNames != null) {
125         view.setExposedContextBeanNames(exposedContextBeanNames);
126     }
127 
128     return view;
129 }

 1 @Override
 2 public void render(@Nullable Map<String, ?> model, HttpServletRequest request,
 3         HttpServletResponse response) throws Exception {
 4 
 5     if (logger.isTraceEnabled()) {
 6         logger.trace("Rendering view with name ‘" + this.beanName + "‘ with model " + model +
 7             " and static attributes " + this.staticAttributes);
 8     }
 9 
10     Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
11     prepareResponse(request, response);
12     renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
13 }
14 
15 就是把一些需要用到的属性放到request中，createMergedOutputModel就是完成这个操作的
16 protected Map<String, Object> createMergedOutputModel(@Nullable Map<String, ?> model,
17         HttpServletRequest request, HttpServletResponse response) {
18 
19     @SuppressWarnings("unchecked")
20     Map<String, Object> pathVars = (this.exposePathVariables ?
21             (Map<String, Object>) request.getAttribute(View.PATH_VARIABLES) : null);
22 
23     // Consolidate static and dynamic model attributes.
24     int size = this.staticAttributes.size();
25     size += (model != null ? model.size() : 0);
26     size += (pathVars != null ? pathVars.size() : 0);
27 
28     Map<String, Object> mergedModel = new LinkedHashMap<>(size);
29     mergedModel.putAll(this.staticAttributes);
30     if (pathVars != null) {
31         mergedModel.putAll(pathVars);
32     }
33     if (model != null) {
34         mergedModel.putAll(model);
35     }
36 
37     // Expose RequestContext?
38     if (this.requestContextAttribute != null) {
39         mergedModel.put(this.requestContextAttribute, createRequestContext(request, response, mergedModel));
40     }
41 
42     return mergedModel;
43 }