【SpringMvc执行流程】SpringMvc如何处理ModelAndView（十一）

发布日期: 2019-07-20

文章字数: 576

阅读时长: 2 分

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示例

@GetMapping(value = "hello")
public MyModelAndView index(String name, ModelAndView modelAndView) {
    modelAndView.addObject("message",name);
    modelAndView.setViewName("index");
    return modelAndView;
}

返回值的处理

由于返回值类型是ModelAndView,不是简单的字符串。这时返回值的处理不再使用ViewNameMethodReturnValueHandler，而是使用了ModelAndViewMethodReturnValueHandler处理的方式来处理。具体处理方法是

public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {

    ModelAndView mav = (ModelAndView) returnValue;
        String viewName = mav.getViewName();
        mavContainer.setViewName(viewName);
    mavContainer.setStatus(mav.getStatus());
    mavContainer.addAllAttributes(mav.getModel());
}

这里只是简单的把视图名(示例中的index)和mav中的model(示例中的message)放入mavContainer。那我们接着看下这个mavContainer后续是如何处理。
由执行顺序可以在RequestMappingHandlerAdapter的invokeHandlerMethod方法看到，下一个对mavcontainer做处理的是getModelAndView方法。

private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {

    ModelMap model = mavContainer.getModel();
    ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model, mavContainer.getStatus());
    return mav;
}

可见mavContainer好像一个容器，把ModelAndView从返回值放入进去，现在又取出来生成新的ModelAndView。跟踪代码，看下新的ModelAndView又被何时处理。发现是在DispatcherServlet的doDispatch方法中的processDispatchResult方法中进行处理。

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
@Nullable MyHandlerExecutionChain mappedHandler, @Nullable MyModelAndView mv,Exception exception) throws Exception {
    // 获取视图view
    render(mv, request, response);
}

此时就调用了一个render方法。

protected void render(MyModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
  //获取适合的view
  view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
  view.render(mv.getModelInternal(), request, response);
}

resolveViewName获取适合的view
render视图渲染页面。

    public void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response) throws Exception {

        Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
        prepareResponse(request, response);
        renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
    }

createMergedOutputModel创建了一个Map对象mergedModel，把model中的信息放入新对map对象mergedModel中。
renderMergedOutputModel是对新mapmergedModel处理。

protected void renderMergedOutputModel(
        Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
        exposeModelAsRequestAttributes(model, request);
 String dispatcherPath = prepareForRendering(request, response);
        RequestDispatcher rd = getRequestDispatcher(request, dispatcherPath);
    rd.forward(request, response);
}

exposeModelAsRequestAttributes 是把model中的信息放入request中

protected void exposeModelAsRequestAttributes(Map<String, Object> model, HttpServletRequest request) throws Exception {
      model.forEach((modelName, modelValue) -> {
        request.setAttribute(modelName, modelValue); 
      });
  }