8、SpringMVC源码分析（3）：分析ModelAndView的形成过程

 1 protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
 2     HttpServletRequest processedRequest = request;
 3     HandlerExecutionChain mappedHandler = null;
 4     boolean multipartRequestParsed = false;
 5 
 6     WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
 7 
 8     try {
 9         ModelAndView mv = null;
10         Exception dispatchException = null;
11 
12         try {
13             processedRequest = checkMultipart(request);
14             multipartRequestParsed = (processedRequest != request);
15 
16             // Determine handler for the current request.
17             mappedHandler = getHandler(processedRequest);
18             if (mappedHandler == null || mappedHandler.getHandler() == null) {
19                 noHandlerFound(processedRequest, response);
20                 return;
21             }
22 
23             // Determine handler adapter for the current request.
24             HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
25 
26             // Process last-modified header, if supported by the handler.
27             String method = request.getMethod();
28             boolean isGet = "GET".equals(method);
29             if (isGet || "HEAD".equals(method)) {
30                 long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
31                 if (logger.isDebugEnabled()) {
32                     logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
33                 }
34                 if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
35                     return;
36                 }
37             }
38 
39             if (!mappedHandler.applyPreHandle(processedRequest, response)) {
40                 return;
41             }
42 
43             // Actually invoke the handler.调用handler方法，返回ModelAndView类型的对象
44             mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
45 
46             if (asyncManager.isConcurrentHandlingStarted()) {
47                 return;
48             }
49 　　　　　　　// 设置mv的Object view属性值，是一个String类型（依据request的URI计算，加上一个前缀和后缀得到）
50             applyDefaultViewName(request, mv);
51             mappedHandler.applyPostHandle(processedRequest, response, mv);
52         }
53         catch (Exception ex) {
54             dispatchException = ex;
55         }
56         processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
57     }
58     catch (Exception ex) {
59         triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
60     }
61     catch (Error err) {
62         triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
63     }
64     finally {
65         if (asyncManager.isConcurrentHandlingStarted()) {
66             // Instead of postHandle and afterCompletion
67             if (mappedHandler != null) {
68                 mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
69             }
70         }
71         else {
72             // Clean up any resources used by a multipart request.
73             if (multipartRequestParsed) {
74                 cleanupMultipart(processedRequest);
75             }
76         }
77     }
78 }

 1 /**
 2  * Invoke the RequestMapping handler method preparing a ModelAndView if view resolution is required.
 3  */
 4 private ModelAndView invokeHandleMethod(HttpServletRequest request,
 5         HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
 6 
 7    //step 1、ModelAndView的前世：是一个ModelAndViewContainer实例
 8    ModelAndViewContainer mavContainer = new ModelAndViewContainer();
 9     
10    /*
11    * RequestContextUtils.getInputFlashMap(request)可以获取到request中的attribute，
12    * 并且将所有的request中的attribute放置在mavContainer中，此时使用的是defaultModel
13    */
14     mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
15     modelFactory.initModel(webRequest, mavContainer, requestMappingMethod);
16    /* 
17     * 在RequestMappingHandlerAdapter中ignoreDefaultModelOnRedirect默认为false
18     */
19     mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
20     
21     //省略许多代码...
22     
23     if (asyncManager.hasConcurrentResult()) {
24             //...
25             mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
26             
27             //...
28         }
29 
30     //step 2、调用handler方法，
31     requestMappingMethod.invokeAndHandle(webRequest, mavContainer);
32     
33     //省略许多代码...
34 
35     //step 3、从mavContainer中获取到ModelAndView实例，返回
36     return getModelAndView(mavContainer, modelFactory, webRequest);
37 }

  1 public class ModelAndViewContainer {
  2     /*
  3      * 对这7个属性我们可以将其分为3个部分来看
  4      */
  5 
  6     // 1、两个模型和一个view，其中view可以存放任何java类型
  7     private Object view;
  8 
  9     // * 注意这个是final类型，也就是不能再重新为defaultModel赋值
 10     private final ModelMap defaultModel = new BindingAwareModelMap();
 11 
 12     private ModelMap redirectModel;
 13 
 14     // 2、记录当前的Model使用策略
 15     private boolean ignoreDefaultModelOnRedirect = false;
 16 
 17     private boolean redirectModelScenario = false;
 18 
 19     // 3、记录request和session的处理状态
 20     private final SessionStatus sessionStatus = new SimpleSessionStatus();
 21 
 22     private boolean requestHandled = false;
 23     
 24   //和view属性相关的处理方法
 25   /*
 26    * 对view的处理主要分为String类型和非String类型。如果views是一个
 27    * String类型的对象，那么它就是下面说的isViewReference
 28    */
 29     public void setViewName(String viewName) {
 30         this.view = viewName;
 31     }
 32     
 33     public String getViewName() {
 34         return (this.view instanceof String ? (String) this.view : null);
 35     }
 36     
 37     public void setView(Object view) {
 38         this.view = view;
 39     }
 40     
 41     public Object getView() {
 42         return this.view;
 43     }
 44     
 45     /*
 46      * 注意，如果veiw是一个String类型，那么isViewReference
 47      */
 48     public boolean isViewReference() {
 49         return (this.view instanceof String);
 50     }
 51     
 52     //和model相关的处理方法
 53     /*
 54      * 假设redirectModelScenario = R ，ignoreDefaultModelOnRedirect = I ，（redirectModel == null）= M
 55      * 那么（R, I, M）共有8中组合情况，useDefaultModel返回false（也就是使用redirectModel）只有三种情况：
 56      * （1,1,0）、（1,1,1）、(1,0,0)
 57      * a：如果同时设置了redirectModelScenario和ignoreDefaultModelOnRedirect为true，那么无论redirectModel
 58      *    是否为null，都会使用redirectModel；
 59      * b：如果设置了redirectModelScenario为true，而ignoreDefaultModelOnRedirect为false，同时redirectModel
 60      *    为null，那么也会使用redirectModel；
 61      */
 62     private boolean useDefaultModel() {
 63         return (!this.redirectModelScenario || (!this.ignoreDefaultModelOnRedirect  && this.redirectModel == null));
 64     }
 65     
 66     /*
 67      * 这个方法是重要的，通过设置redirectModelScenario和ignoreDefaultModelOnRedirect来影响该方法的返回值；
 68      * 如果没有初始化redirectModel，那么就会new一个ModelMap对象进行返回；
 69      */
 70     public ModelMap getModel() {
 71         if (useDefaultModel()) {
 72             return this.defaultModel;
 73         }
 74         else {
 75             return (this.redirectModel != null) ? this.redirectModel : new ModelMap();
 76         }
 77     }
 78     
 79     public ModelMap getDefaultModel() {
 80         return this.defaultModel;
 81     }
 82     
 83     public void setRedirectModel(ModelMap redirectModel) {
 84         this.redirectModel = redirectModel;
 85     }
 86     
 87     /**
 88      * Whether the controller has returned a redirect instruction, e.g. a
 89      * "redirect:" prefixed view name, a RedirectView instance, etc.
 90      */
 91     public void setRedirectModelScenario(boolean redirectModelScenario) {
 92         this.redirectModelScenario = redirectModelScenario;
 93     }
 94     
 95     public void setIgnoreDefaultModelOnRedirect(boolean ignoreDefaultModelOnRedirect) {
 96         this.ignoreDefaultModelOnRedirect = ignoreDefaultModelOnRedirect;
 97     }
 98     
 99     //省略一些方法...
100 }

 1 /**
 2  *Invokes the method and handles the return value through one of the configured HandlerMethodReturnValueHandlers.
 3  */
 4 public void invokeAndHandle(ServletWebRequest webRequest,
 5         ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {
 6     
 7     // 调用handler方法，的到返回结果为returnValue
 8     Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
 9     setResponseStatus(webRequest);
10 
11     if (returnValue == null) {//handler返回null
12         if (isRequestNotModified(webRequest) || hasResponseStatus() || mavContainer.isRequestHandled()) {
13             mavContainer.setRequestHandled(true);
14             return;
15         }
16     }else if (StringUtils.hasText(this.responseReason)) {
17         mavContainer.setRequestHandled(true);
18         return;
19     }
20 
21     // 设置标志位，表示当前request请求还没有处理完成
22     mavContainer.setRequestHandled(false);
23     try {
24         // 处理返回结果returnValue
25         this.returnValueHandlers.handleReturnValue(
26                 returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
27     }catch (Exception ex) {
28         if (logger.isTraceEnabled()) {
29             logger.trace(getReturnValueHandlingErrorMessage("Error handling return value", returnValue), ex);
30         }
31         throw ex;
32     }
33 }

 1 public void handleReturnValue(Object returnValue, MethodParameter returnType,
 2         ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
 3 
 4     //寻找能够处理returnType类型的HandlerMethodReturnValueHandler实例
 5     HandlerMethodReturnValueHandler handler = getReturnValueHandler(returnType);
 6     
 7     //如果没有找到对应的HandlerMethodReturnValueHandler，则会返回一个异常
 8     Assert.notNull(handler, "Unknown return value type [" + returnType.getParameterType().getName() + "]");
 9     
10     //用上面寻找到的handler来处理返回结果
11     handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
12 }

 1 /**
 2  * Find a registered HandlerMethodReturnValueHandler that supports the given return type
 3  */
 4 private HandlerMethodReturnValueHandler getReturnValueHandler(MethodParameter returnType) {
 5     /*
 6      * returnValueHandlers是List<HandlerMethodReturnValueHandler>类型，
 7      * 在调试的时候可以看到它共包含了13个对象。还可以增减吗？？如何注
 8      * 册一个returnValueHandler呢？？有待探究。
 9      */
10     for (HandlerMethodReturnValueHandler returnValueHandler : returnValueHandlers) {
11         if (logger.isTraceEnabled()) {
12             logger.trace("Testing if return value handler [" + returnValueHandler + "] supports [" +
13                     returnType.getGenericParameterType() + "]");
14         }
15         if (returnValueHandler.supportsReturnType(returnType)) {
16             return returnValueHandler;
17         }
18     }
19     return null;
20 }

 1 public class ViewNameMethodReturnValueHandler implements HandlerMethodReturnValueHandler {
 2 
 3     private String[] redirectPatterns;
 4 
 5     public void setRedirectPatterns(String... redirectPatterns) {
 6         this.redirectPatterns = redirectPatterns;
 7     }
 8 
 9     public String[] getRedirectPatterns() {
10         return this.redirectPatterns;
11     }
12 
13 
14     @Override
15     public boolean supportsReturnType(MethodParameter returnType) {
16         Class<?> paramType = returnType.getParameterType();
17         return (void.class.equals(paramType) || String.class.equals(paramType));
18     }
19 
20     @Override
21     public void handleReturnValue(Object returnValue, MethodParameter returnType,
22             ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
23 
24         if (returnValue == null) {
25             return;
26         }
27         else if (returnValue instanceof String) {
28             String viewName = (String) returnValue;
29             
30             // 对mavContainer的设置就是将view属性赋值为returnValue
31             mavContainer.setViewName(viewName);
32             
33             /* 如果returnValue指示为redirect（比如说"redirect:"前缀，redirect pattern的设置等）
34              * 则将设置redirectModelScenario为true。
35              */
36             if (isRedirectViewName(viewName)) {
37                 mavContainer.setRedirectModelScenario(true);
38             }
39         }
40         else {
41             // should not happen
42             throw new UnsupportedOperationException("Unexpected return type: " +
43                     returnType.getParameterType().getName() + " in method: " + returnType.getMethod());
44         }
45     }
46 
47     /**
48      * Whether the given view name is a redirect view reference.
49      * The default implementation checks the configured redirect patterns and
50      * also if the view name starts with the "redirect:" prefix.
51      * @param viewName the view name to check, never {@code null}
52      * @return "true" if the given view name is recognized as a redirect view
53      * reference; "false" otherwise.
54      */
55     protected boolean isRedirectViewName(String viewName) {
56         if (PatternMatchUtils.simpleMatch(this.redirectPatterns, viewName)) {
57             return true;
58         }
59         return viewName.startsWith("redirect:");
60     }
61 
62 }

 1 private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,
 2         ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {
 3 
 4     modelFactory.updateModel(webRequest, mavContainer);
 5     if (mavContainer.isRequestHandled()) {
 6         return null;
 7     }
 8     
 9     //得到defaultModel或者是redirectModel
10     ModelMap model = mavContainer.getModel();
11     
12     /*
13      * 注意mavContainer.getViewName()方法，如果mavContainer的Object view是一个String类型，
14      * 则返回该字符串；如果不是，则得到null
15      */
16     ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model);
17     
18     if (!mavContainer.isViewReference()) {
19         mav.setView((View) mavContainer.getView());
20     }
21     if (model instanceof RedirectAttributes) {
22         Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes();
23         HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
24         RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
25     }
26     return mav;
27 }