这篇博文讨论的问题是从ModelAndView如何渲染到页面。
首先要知道每个请求处理完之后都会返回一个ModelAndView对象。
这里我分6种情况来分析，代表6种返回类型：
我先贴出我的测试的后台代码：
<?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/mvc http://www.springframework.org/schema/mvc/spring-mvc-4.0.xsd 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-4.0.xsd"> <!-- 配置扫描的包 --> context:component-scan base-package="com"></context:component-scan> 配置视图解析器，将方法的返回值映射到一个实际的物理视图 bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"> property name="prefix" value="/pages/result/"property="suffix"=".jsp"</beanmvc:default-servlet-handler/> mvc:annotation-driven> beans>
package com.mmc.modelandview; import java.util.Date; java.util.Map; org.springframework.stereotype.Controller; org.springframework.ui.Model; org.springframework.web.bind.annotation.RequestMapping; org.springframework.web.bind.annotation.SessionAttributes; org.springframework.web.servlet.ModelAndView; org.springframework.web.servlet.View; org.springframework.web.servlet.view.InternalResourceView; org.springframework.web.servlet.view.jasperreports.JasperReportsPdfView; com.mmc.common.CommonParam; @Controller public TestModelAndView { @RequestMapping("testModelAndView") public ModelAndView testModelAndView(){ ModelAndView modelAndView=new ModelAndView(CommonParam.SUCCESS); modelAndView.addObject("time", Date()); return modelAndView; } @RequestMapping("testModel" String testModel(Model model){ model.addAttribute("time",1)"> CommonParam.SUCCESS; } @RequestMapping("testMap"public String testMap(Map<String,Object> map){ map.put("person","lixiaolu"); CommonParam.SUCCESS; } @RequestMapping("testView" View testView(View view){ view= JasperReportsPdfView(); view; } @RequestMapping("testString" String testString(){ CommonParam.SUCCESS; } @RequestMapping("testForward" String testForward(){ return "forward:/hello"; } @RequestMapping("testVoid"void testVoid(){ System.out.println("执行testVoid方法"); } }
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 = ; Exception dispatchException = ; { processedRequest = checkMultipart(request); multipartRequestParsed = processedRequest != request; // Determine handler for the current request. mappedHandler = getHandler(processedRequest); if (mappedHandler == null || mappedHandler.getHandler() == ) { noHandlerFound(processedRequest,response); ; } Determine handler adapter for the current request. 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 (logger.isDebugEnabled()) { String requestUri = urlPathHelper.getRequestUri(request); logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified); } if (new ServletWebRequest(request,response).checkNotModified(lastModified) && isGet) { ; } } if (!mappedHandler.applyPreHandle(processedRequest,response)) { { Actually invoke the handler. mv = ha.handle(processedRequest,response,mappedHandler.getHandler()); } finally (asyncManager.isConcurrentHandlingStarted()) { ; } } //检查view有没有设置，如果没有给他设置一个默认的 applyDefaultViewName(request,mv);
//传给我们的拦截器，也就是说在拦截器里我们可以操作视图的映射 mappedHandler.applyPostHandle(processedRequest,mv); } catch (Exception ex) { dispatchException = ex; }
//就是去处理映射了 processDispatchResult(processedRequest,mappedHandler,mv,dispatchException); } (Exception ex) { triggerAfterCompletion(processedRequest,ex); } (Error err) { triggerAfterCompletionWithError(processedRequest,err); } { (asyncManager.isConcurrentHandlingStarted()) { Instead of postHandle and afterCompletion mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest,response); ; } Clean up any resources used by a multipart request. (multipartRequestParsed) { cleanupMultipart(processedRequest); } } }
这个方法进去之后，经过一些判断，会执行到一个render(mv,request,response);方法，这个方法就是渲染视图的方法。这个方法进去之后
protected void render(ModelAndView mv,HttpServletRequest request,HttpServletResponse response) throws Exception { // Determine locale for request and apply it to the response. Locale locale = this.localeResolver.resolveLocale(request);
response.setLocale(locale); View view; (mv.isReference()) { We need to resolve the view name.
//返回一个View对象
view = resolveViewName(mv.getViewName(),mv.getModelInternal(),locale,request); if (view == ) { throw ServletException( "Could not resolve view with name '" + mv.getViewName() + "' in servlet with name '" + getServletName() + "'"); } } else No need to lookup: the ModelAndView object contains the actual View object. view = mv.getView(); new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " + "View object in servlet with name '" + getServletName() + "'"); } } Delegate to the View object for rendering. (logger.isDebugEnabled()) { logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'"); } {
//渲染视图 view.render(mv.getModelInternal(),response); } (Exception ex) { (logger.isDebugEnabled()) { logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'",ex); } throw ex; } }
@Override void render(Map<String,?> model,1)"> Exception { (logger.isTraceEnabled()) { logger.trace("Rendering view with name '" + this.beanName + "' with model " + model + " and static attributes " + this.staticAttributes); } //将我ModelAndView中modelAndView.addObject("time",new Date());的值放入mergeModel中 Map<String,Object> mergedModel = createMergedOutputModel(model,response); //判断是否读取本地缓存 prepareResponse(request,response);
//进一步处理，下面贴出它的代码 renderMergedOutputModel(mergedModel,response); }@Overrivoid renderMergedOutputModel(
Map<String,Object> model,1)"> Exception { Determine which request handle to expose to the RequestDispatcher.
//确定哪些请求处理暴露给RequestDispatcher。
HttpServletRequest requestToExpose = getRequestToExpose(request); Expose the model object as request attributes.
//把model里面的值放入request中
exposeModelAsRequestAttributes(model,requestToExpose); Expose helpers as request attributes,if any. exposeHelpers(requestToExpose); Determine the path for the request dispatcher.
//获取要返回的地址
String dispatcherPath = prepareForRendering(requestToExpose,response); Obtain a RequestDispatcher for the target resource (typically a JSP).
//确定一个请求处理器为这些参数资源
RequestDispatcher rd = getRequestDispatcher(requestToExpose,dispatcherPath); if (rd == ) { new ServletException("Could not get RequestDispatcher for [" + getUrl() + "]: Check that the corresponding file exists within your web application archive!"); } If already included or response already committed,perform include,else forward. (useInclude(requestToExpose,response)) { response.setContentType(getContentType()); (logger.isDebugEnabled()) { logger.debug("Including resource [" + getUrl() + "] in InternalResourceView '" + getBeanName() + "'"); } rd.include(requestToExpose,response); } Note: The forwarded resource is supposed to determine the content type itself. (logger.isDebugEnabled()) { logger.debug("Forwarding to resource [" + getUrl() + "] in InternalResourceView '" + getBeanName() + "'"); } rd.forward(requestToExpose,response); } }
当要转发的地址，和要携带的信息都放入到requestToExpose里之后，就调用rd.forward(requestToExpose,response);转发请求到页面。
InvocableHandlerMethod类中有下面的方法：
final Object invokeForRequest(NativeWebRequest request,ModelAndViewContainer mavContainer,Object... providedArgs) Exception { //mavContainer对象初始化时，会初始化一个默认的BindingAwareModelMap属性。将默认的这个BindingAwareModelMap属性放入arg
Object[] args = getMethodArgumentValues(request,mavContainer,providedArgs); if (logger.isTraceEnabled()) { StringBuilder sb = new StringBuilder("Invoking ["); sb.append(this.getBeanType().getSimpleName()).append("."); sb.append(getMethod().getName()).append("] method with arguments "); sb.append(Arrays.asList(args)); logger.trace(sb.toString()); }
//执行我的业务方法，把arg数组传入，把我里面的mavContainer默认的modelMap赋上值 Object returnValue = invoke(args); (logger.isTraceEnabled()) { logger.trace("Method [" + getMethod().getName() + "] returned [" + returnValue + "]" returnValue; }
然后将model取出来，和我返回的String一起构建ModelAndView对象。
private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,ModelFactory modelFactory,NativeWebRequest webRequest) Exception { modelFactory.updateModel(webRequest,mavContainer); (mavContainer.isRequestHandled()) { return ; }
//取出model ModelMap model = mavContainer.getModel();
//构建对象 ModelAndView mav = new ModelAndView(mavContainer.getViewName(),model); mavContainer.isViewReference()) { mav.setView((View) mavContainer.getView()); } if (model instanceof RedirectAttributes) { Map<String,?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes(); HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.); RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes); } mav; }
需要分析的就是我们加入model中的参数是怎么加入到modelAndView对象的。
其实是和Map类型也是一样的，将
mavContainer对象初始化时，会初始化一个默认的BindingAwareModelMap属性。将默认的这个BindingAwareModelMap属性放入arg，然后把arg传入我们的业务方法，然后业务方法接收到这个参数，往这个参数放值。就像我的例子里那样
CommonParam.SUCCESS;
}
放好之后，model就有值了，然后根据这个model和我返回的字符串一起构建ModelAndView对象。
这种我还没搞懂怎么用
这个类ServletInvocableHandlerMethod的方法里：
final invokeAndHandle(ServletWebRequest webRequest,1)"> Exception { //这里返回我的String类型的值 Object returnValue = invokeForRequest(webRequest,providedArgs); setResponseStatus(webRequest); if (returnValue == if (isRequestNotModified(webRequest) || hasResponseStatus() || mavContainer.isRequestHandled()) { mavContainer.setRequestHandled(true); ; } } else if (StringUtils.hasText(.responseReason)) { mavContainer.setRequestHandled(); ; } mavContainer.setRequestHandled(); {
//进一步处理返回值 .returnValueHandlers.handleReturnValue(returnValue,getReturnValueType(returnValue),webRequest); } (logger.isTraceEnabled()) { logger.trace(getReturnValueHandlingErrorMessage("Error handling return value" ex; } }
然后到ViewNameMethodReturnValueHandler类的这个方法里：
handleReturnValue( Object returnValue,MethodParameter returnType,NativeWebRequest webRequest) ; } if (returnValue String) {
//把返回值赋给mavContainer的ViewName String viewName = (String) returnValue; mavContainer.setViewName(viewName); (isRedirectViewName(viewName)) { mavContainer.setRedirectModelScenario( should not happen new UnsupportedOperationException("Unexpected return type: " + returnType.getParameterType().getName() + " in method: " + returnType.getMethod()); } }
然后通过mavContainer对象来构造一个ModelAndView对象，然后渲染视图。
第五种特别篇：返回值中带有redirect的字符串
在ViewNameMethodReturnValueHandler类中的handleReturnValue方法中：
//同样是把带有redirect的字符串赋给mavContainer对象。 String viewName (String) returnValue; mavContainer.setViewName(viewName); returnType.getMethod()); } }
然后在DispatcherServlet类中有这个方法：
protected View resolveViewName(String viewName,Map<String,1)"> model,Locale locale,HttpServletRequest request) for (ViewResolver viewResolver : .viewResolvers) {
//获取view，View是一个接口，这里的view实际类型是RedirectView View view = viewResolver.resolveViewName(viewName,locale); if (view != view; } } ; }
然后根据View类型的不同，调用的也是不同的renderMergedOutputModel方法，这是RedirectView类的方法：
void renderMergedOutputModel(Map<String,HttpServletResponse response) IOException { String targetUrl = createTargetUrl(model,request); targetUrl = updateTargetUrl(targetUrl,model,response); FlashMap flashMap = RequestContextUtils.getOutputFlashMap(request); CollectionUtils.isEmpty(flashMap)) { UriComponents uriComponents = UriComponentsBuilder.fromUriString(targetUrl).build(); flashMap.setTargetRequestPath(uriComponents.getPath()); flashMap.addTargetRequestParams(uriComponents.getQueryParams()); FlashMapManager flashMapManager = RequestContextUtils.getFlashMapManager(request); if (flashMapManager == new IllegalStateException("FlashMapManager not found despite output FlashMap having been set"); } flashMapManager.saveOutputFlashMap(flashMap,response); } sendRedirect(request,targetUrl,.http10Compatible); }
然后就是response.sendRedirect(encodedRedirectURL);
第五种特别篇之带forward的字符串：
void render(ModelAndView mv,1)"> Determine locale for request and apply it to the response. Locale locale = .localeResolver.resolveLocale(request); response.setLocale(locale); View view; We need to resolve the view name.
//选择不同的类型的视图处理器构建视图对象
{ view.render(mv.getModelInternal(),response); } ex; } }
这个是DispatcherServlet中的resolveViewName方法。
然后是选择了AbstractCachingViewResolver这个视图处理器的resolveViewName方法，去创建视图。然后调用了他的子类UrlBasedViewResolver的创建视图方法：
protected View createView(String viewName,Locale locale) If this resolver is not supposed to handle the given view, return null to pass on to the next resolver in the chain. canHandle(viewName,locale)) { Check for special "redirect:" prefix. (viewName.startsWith(REDIRECT_URL_PREFIX)) { String redirectUrl = viewName.substring(REDIRECT_URL_PREFIX.length()); RedirectView view = RedirectView(redirectUrl,isRedirectContextRelative(),isRedirectHttp10Compatible()); applyLifecycleMethods(viewName,view); } Check for special "forward:" prefix.
//获得一个forwardUrl
if (viewName.startsWith(FORWARD_URL_PREFIX)) { String forwardUrl = viewName.substring(FORWARD_URL_PREFIX.length()); return new InternalResourceView(forwardUrl); } Else fall back to superclass implementation: calling loadView. super.createView(viewName,locale); }
然后调用InternalResourceView类的renderMergedOutputModel方法：
renderMergedOutputModel( Map<String,1)"> Determine which request handle to expose to the RequestDispatcher. HttpServletRequest requestToExpose = Expose the model object as request attributes. Determine the path for the request dispatcher. String dispatcherPath = Obtain a RequestDispatcher for the target resource (typically a JSP). RequestDispatcher rd =); }
//调用转发方法 rd.forward(requestToExpose,response); } }
这时我们需要考虑两个问题，第一：返回值是Void也就是没有返回值，他的ModalAndView对象是什么样的？第二：他将转到哪个页面，还是会直接报错？
带着这两个问题，我们看源码：
以DispatcherServlet中的这句代码往下看，
mv = ha.handle(processedRequest,mappedHandler.getHandler());
一直到ServletInvocableHandlerMethod类的这个方法
Exception { Object returnValue = if (returnValue == null) { if (isRequestNotModified(webRequest) || hasResponseStatus() || mavContainer.isRequestHandled()) { mavContainer.setRequestHandled(true); return; } } {
//主要看这里，handleReturnValue，处理返回值，那我们点进去看看他怎么处理null值 ex; } }
然而结果就是他看到return是null，什么都没处理就返回了，只好再往下看。
; } } //最后发现view为null时，这里处理了 applyDefaultViewName(request,mv); mappedHandler.applyPostHandle(processedRequest,mv); } ex; } processDispatchResult(processedRequest,dispatchException); } (multipartRequestParsed) { cleanupMultipart(processedRequest); } } }
接下来是组装地址的方法：这个是处理地址组装的类UrlBasedViewResolver
protected View loadView(String viewName,1)"> Exception {
//进行组装 AbstractUrlBasedView view buildView(viewName); View result =return (view.checkResource(locale) ? result : ); }
protected AbstractUrlBasedView buildView(String viewName) Exception { AbstractUrlBasedView view = (AbstractUrlBasedView) BeanUtils.instantiateClass(getViewClass());
//对应的我最上方spring.mvc里面的prefix和suffix的配置的地址，把它们连接起来 view.setUrl(getPrefix() + viewName + getSuffix()); String contentType = getContentType(); if (contentType != ) { view.setContentType(contentType); } view.setRequestContextAttribute(getRequestContextAttribute()); view.setAttributesMap(getAttributesMap()); this.exposePathVariables != ) { view.setExposePathVariables(exposePathVariables); } view; }
到此，要转向哪一个地址，ModelAndView对象是什么样都已经大致清楚了。然后就是调用rd.forward(requestToExpose,response);方法，渲染到页面
里面代码很多，思路也不是很清楚。有意义的地方只是给小伙伴们提供了几个方向，要想看springMvc是如何渲染视图的，可以从他的返回类型入手，然后debug一步步的看。源码我是在这里：
https://mvnrepository.com/search?q=spring-ui&p=2 下载的。我这里用的是4.0.0的版本。最后在总结一下吧。
首先，要构造一个ModelAndView对象，这个对象的构建思路是，我创建一个数组，把一个对象放在这个数组里，然后把数组给你，你往这个数组里放值，然后我去取这个数组里的值。然后获取的值我拿来
创建一个ModelAndView对象。
第二步，去渲染视图，有很多的渲染视图的处理器，系统会去判断选择一个处理器，来处理你的请求，大概的不同就是，我最终是调doFord还是doRedirect，我的返回值的header应该设置什么等等。
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