SpringMVC工作流程

DispatcherServlet 为 SpringMVC 处理 servlet 的入口.

在 doService 方法中调用 doDispatcher 方法，也就是说业务逻辑主要是在 doDispatcher 中实现.

HandlerMapping 抽象了请求 URL 到请求处理器之间的映射. 当一个请求过来时，DispatcherServlet 会轮询 HandlerMapping 那个请求处理器能处理.

实际上处理请求的是 RequestMappingHandlerMapping 这个类.

HandlerExecutionChain 的字面意思就能够表达清了. 它的概念是 handler 执行的链式结构.

当执行 HandlerExecutionChain handler = hm.getHandler(request); 这段代码后，将调转到 AbstractHandlerMethodMapping.getHandlerInternal 方法.

lookupHandlerMethod 方法返回的是 HandlerMethod 对象. 这个的概念，我理解是类似于反射的机制，用于执行方法.

PS: SpringMVC 的 DispatcherServlet 的设计理念和 OFBiz 关于 Web MVC 的设计很相似，只不过的是 OFBiz 这块的设计是通过 XML 文件实现的，而 Spring MVC 是通过注解实现的. 后续有计划将 OFBiz 有关 XML 的解析替换成注解的方式，来简化工作量.

关于为啥要构造 HandlerExecutionChain 这个对象，是可以在执行实际方法之前，执行某些 HandlerInterceptor.

getHandler 方法会做两步：
1.获取实际的执行方法.
2.构造 HandlerExecutionChain.

经过上面的步骤，我们可以获得 HandlerExecutionChain 对象. 然后进一步的获取 HandlerAdapter 对象.

HandlerAdapter 是啥概念了？HandlerAdapter 是对上面 handler 对象的包装. 或者说 HandlerAdapter 是一个桥梁，承接处理和 ModelView.

然后预执行. 预执行的作用是：比如说我有拦截器，当不满足条件的时候可以跳过. 就不会执行实际的代码.
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}

实际执行.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

承接代码执行和 ModelView.
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {

    return handleInternal(request, response, (HandlerMethod) handler);
}

实际执行(调用方法)
invocableMethod.invokeAndHandle(webRequest, mavContainer);

返回结果.
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);

返回视图.
private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,
ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {

    modelFactory.updateModel(webRequest, mavContainer);
    if (mavContainer.isRequestHandled()) {
        return null;
    }
    ModelMap model = mavContainer.getModel();
    // ModelAndView: reference to view with name '/login.html'; model is {} 为调试信息.
    ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model, mavContainer.getStatus());
    if (!mavContainer.isViewReference()) {
        mav.setView((View) mavContainer.getView());
    }
    if (model instanceof RedirectAttributes) {
        Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes();
        HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
        if (request != null) {
            RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
        }
    }
    return mav;
}

处理视图.
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);

渲染——感觉 Spring 关于 MVC 的处理逻辑和 OFBiz 非常像，后续在做进一步的验证.
protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
View view;
String viewName = mv.getViewName();
if (viewName != null) {
// We need to resolve the view name.
view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
if (view == null) {
throw new ServletException(“Could not resolve view with name '” + mv.getViewName() +
“’ in servlet with name '” + getServletName() + “’”);
}
}

    try {
        if (mv.getStatus() != null) {
            response.setStatus(mv.getStatus().value());
        }
        view.render(mv.getModelInternal(), request, response);
    }
    catch (Exception ex) {
        if (logger.isDebugEnabled()) {
            logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name '" +
                    getServletName() + "'", ex);
        }
        throw ex;
    }
}

protected final void renderMergedOutputModel(
Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {

    if (this.exposeSpringMacroHelpers) {
        if (model.containsKey(SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE)) {
            throw new ServletException(
                    "Cannot expose bind macro helper '" + SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE +
                    "' because of an existing model object of the same name");
        }
        // Expose RequestContext instance for Spring macros.
        model.put(SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE,
                new RequestContext(request, response, getServletContext(), model));
    }

    applyContentType(response);

    renderMergedTemplateModel(model, request, response);
}

补充一点：

Controller 注解和 RequestMapping 注解在哪里被解析的？