Spring Mvc 请求流程

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protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    ... 
    try {
        ...
        try {
            // 检查是否为文件上传
            processedRequest = checkMultipart(request);

            // 获取 HandlerMapping  
            mappedHandler = getHandler(processedRequest);
            if (mappedHandler == null) {
                // 40
                noHandlerFound(processedRequest, response);
                return;
            }
            // 获取 HandlerAdapter
            HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
            ...
            // 执行 HandlerInterceptor#preHandle
            if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                return;
            }
            // 执行请求
            mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
            ...
            // 执行 HandlerInterceptor#postHandle
            mappedHandler.applyPostHandle(processedRequest, response, mv);
        }
        catch (Exception ex) {
            dispatchException = ex;
        }
        catch (Throwable err) {
            dispatchException = new NestedServletException("Handler dispatch failed", err);
        }
        // 处理异常，然后执行 HandlerInterceptor#afterCompletion
        processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
    }
    catch (Exception ex) {
        // 执行 HandlerInterceptor#afterCompletion
        triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
    }
    catch (Throwable err) {
        // 执行 HandlerInterceptor#afterCompletion
        triggerAfterCompletion(processedRequest, response, mappedHandler,
                new NestedServletException("Handler processing failed", err));
    }
    finally {
        ...
    }
}