【SpringMVC 笔记】6、请求处理的大致流程

请求处理的大致流程

1）所有请求过来，DispatcherServlet收到请求
2）调用doDispatch()方法进行处理

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 = null;
        Object dispatchException = null;

        try {
            //1.首先判断当前请求是否是文件上传请求
            processedRequest = this.checkMultipart(request);
            multipartRequestParsed = processedRequest != request;

            //2.getHandler()获取能够处理该请求的前端控制器
   /*ioc容器启动时创建每个组件对象时
     会扫描每个Cintroller对象的RequestMapping收集其可以处理的请求，并将这些信息保存在HandlerMapping的HandlerMap中
    当请求过来时查看哪个HandlerMap有对应的处理请求，则返回该处理请求所在的前端控制器

   */
            mappedHandler = this.getHandler(processedRequest);

            //3.如果没找到合适的处理器就404，或者抛异常
            if (mappedHandler == null) {
                this.noHandlerFound(processedRequest, response);
                return;
            }

            //4、getHandlerAdapter()拿到能够执行这个类的所有方法的适配器（反射工具AnnotationMethodHandlerAdapter能解析注解方法的适配器）
            HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());

            //5、获取请求方式：POST、GET等
            String method = request.getMethod();
            boolean isGet = "GET".equals(method);

            if (isGet || "HEAD".equals(method)) {
                long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                if (this.logger.isDebugEnabled()) {
                    this.logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
                }

                if ((new ServletWebRequest(request, response)).checkNotModified(lastModified) && isGet) {
                    return;
                }
            }

            if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                return;
            }

            //6.用适配器执行目标方法，方法返回值作为视图名，设置保存到ModelAndView中
              //目标方法无论怎么写，最终适配器执行完成后都会将执行完成的结果封装成ModelAndView
            mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
            if (asyncManager.isConcurrentHandlingStarted()) {
                return;
            }

            this.applyDefaultViewName(processedRequest, mv);
            mappedHandler.applyPostHandle(processedRequest, response, mv);
        } catch (Exception var20) {
            dispatchException = var20;
        } catch (Throwable var21) {
            dispatchException = new NestedServletException("Handler dispatch failed", var21);
        }

        //7.根据方法最终执行完后的封装的ModelAndView:转发到对应页面，而且ModelAndView中的数据可以在请求域中获取
        this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException);
    } catch (Exception var22) {
        this.triggerAfterCompletion(processedRequest, response, mappedHandler, var22);
    } catch (Throwable var23) {
        this.triggerAfterCompletion(processedRequest, response, mappedHandler, new NestedServletException("Handler processing failed", var23));
    } finally {
        if (asyncManager.isConcurrentHandlingStarted()) {
            if (mappedHandler != null) {
                mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
            }
        } else if (multipartRequestParsed) {
            this.cleanupMultipart(processedRequest);
        }

    }
}