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SpingMVC解析

SpingMVC解析

作者: yht_humble | 来源:发表于2017-10-19 18:15 被阅读0次
    springMVC (2).jpg

    这是一个最经典的SpringMVC执行流程图,其中最核心的三个地方是: HandlerMappingHandlerAdapterHttpMessageConverter

    首先,从DispatcherServlet入手,先看下DispatcherServlet继承图:

    DispatcherServlet.png

    从图可以得知,DispatcherServlet本质上就是Servlet,那么Servlet生命周期最主要的的三个方法时:void init(ServletConfig config),void service(ServletRequest request,ServletResponse response),void destroy()。
    看了源代码之后发现DispatcherServlet里面根本没有service这个方法,这个时候找到它的父类FrameworkServlet ,


    sercice.png processRequest.png doService.png

    doDispatch,最主要的方法,用来分发请求,核心的逻辑都在这里面(截图有限,自己看源码吧)

    doDispatcher.png doDispatcher2.png

    主要的:
    1.checkMultipart方法检查是否是二进制的请求(文件上传的请求)

    checkMultipart.png

    2.mappingHandler=getHandler(request)

    doDispatcher (2).png

    返回的是HandlerExecutionChain(处理执行链)

    DispatcherServlet (2).png

    再看DispatcherServlet.properties其实就是包装了不同的Mapping来判断通过何种方式来配置。

    HandlerExecutionChain(处理执行链)包含两部分内容,一部分是请求对应的控制器,一部分是拦截器,真正执行handle之前,有一系列操作,例如数据转换,格式化,数据验证这些,都是由拦截器来做的

    另外需要注意的是,假如你自定义了n个拦截器,会发现HandlerExecutionChain会有n+1个拦截器,说明有一个是他内部有的,从这里我们可以知道它的执行顺序,比如这里要先执行拦截器,再执行我们控制器,所以这个东西被称为处理执行链

    3.ha = getHandlerAdapter(mappedHandler.getHandler());

    ![Uploading applyPreHandler_524696.png . . .]

    getHandlerAdapter.png

    HandlerAdapater(处理器适配器),用来执行handler(控制器,即contorller)
    这里判断handler适不适合这个RequestMappingAdapter,适合就返回

    if(ha.supports(handler))
             return ha;
    

    获取方法类型

    String method = reqyest,getMethod();
    
     if(!mappedHandler.applyPreHandle(processedRequest, response)){
                return;
      }
    
    applyPreHandler.png

    这里主要遍历拦截器。

    // Actually invoke the handler.
      mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
    

    这里去调用handler方法,这个方法会做很多事情,比如参数自动装入。

    然后是

        @RequestMapping(value = "/golist.do")
        public ModelAndView golist(HttpServletRequest request) {
            return new ModelAndView("/views/module/advise/list.jsp");
        }
    

    再继续

    //默认视图名称
     applyDefaultViewName(request, mv);
    

    像下面这个 返回的只有model 没有 view

    @RequestMapping(value = "/saveEntity.do")
        public @ResponseBody AjaxResult saveByEntity(HttpServletRequest request, Advise entity) {
            LoginUser loginUser = LoginUserUtil.getCurrentUser(request);
            adviseService.saveEntity(loginUser, entity);
            return AjaxResult.warpAjaxResult(true);
    }
    

    继续往下

     mappedHandler.applyPostHandle(processedRequest, response, mv);
    
     void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv)
            throws Exception
        {
            if(getInterceptors() == null)
                return;
            for(int i = getInterceptors().length - 1; i >= 0; i--)
            {
                HandlerInterceptor interceptor = getInterceptors()[i];
                interceptor.postHandle(request, response, handler, mv);
            }
        }
    

    从这里我们知道,Interceptor的执行顺序是反过来的:如图

    Interceptor.png

    再继续

     processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
    
      private void processDispatchResult(HttpServletRequest request, HttpServletResponse response, HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception)
            throws Exception
        {
            boolean errorView = false;
            if(exception != null)
                if(exception instanceof ModelAndViewDefiningException)
                {
                    logger.debug("ModelAndViewDefiningException encountered", exception);
                    mv = ((ModelAndViewDefiningException)exception).getModelAndView();
                } else
                {
                    Object handler = mappedHandler == null ? null : mappedHandler.getHandler();
                    mv = processHandlerException(request, response, handler, exception);
                    errorView = mv != null;
                }
            if(mv != null && !mv.wasCleared())
            {
                render(mv, request, response);
                if(errorView)
                    WebUtils.clearErrorRequestAttributes(request);
            } else
            if(logger.isDebugEnabled())
                logger.debug((new StringBuilder()).append("Null ModelAndView returned to DispatcherServlet with name '").append(getServletName()).append("': assuming HandlerAdapter completed request handling").toString());
            if(WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted())
                return;
            if(mappedHandler != null)
                mappedHandler.triggerAfterCompletion(request, response, null);
        }
    
     protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response)
            throws Exception
        {
            Locale locale = localeResolver.resolveLocale(request);
            response.setLocale(locale);
            View view;
            if(mv.isReference())
            {
                view = resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request);
                if(view == null)
                    throw new ServletException((new StringBuilder()).append("Could not resolve view with name '").append(mv.getViewName()).append("' in servlet with name '").append(getServletName()).append("'").toString());
            } else
            {
                view = mv.getView();
                if(view == null)
                    throw new ServletException((new StringBuilder()).append("ModelAndView [").append(mv).append("] neither contains a view name nor a ").append("View object in servlet with name '").append(getServletName()).append("'").toString());
            }
            if(logger.isDebugEnabled())
                logger.debug((new StringBuilder()).append("Rendering view [").append(view).append("] in DispatcherServlet with name '").append(getServletName()).append("'").toString());
            try
            {
                //这里决定究竟是转发还是重定向,或者说变成其他视图
                view.render(mv.getModelInternal(), request, response);
            }
            catch(Exception ex)
            {
                if(logger.isDebugEnabled())
                    logger.debug((new StringBuilder()).append("Error rendering view [").append(view).append("] in DispatcherServlet with name '").append(getServletName()).append("'").toString(), ex);
                throw ex;
            }
        }
    
      public void render(Map model, HttpServletRequest request, HttpServletResponse response)
            throws Exception
        {
            if(logger.isTraceEnabled())
                logger.trace((new StringBuilder()).append("Rendering view with name '").append(beanName).append("' with model ").append(model).append(" and static attributes ").append(staticAttributes).toString());
            Map mergedModel = createMergedOutputModel(model, request, response);
            prepareResponse(request, response);
            renderMergedOutputModel(mergedModel, request, response);
        }
    

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