springMVC doDispatch方法

最新推荐文章于 2025-05-23 19:56:09 发布

yushuifirst

最新推荐文章于 2025-05-23 19:56:09 发布

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分类专栏： spring

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本文详细解析了Spring MVC框架中核心组件DispatcherServlet的工作流程。从请求处理到响应生成，包括拦截器的应用、视图渲染等关键步骤。

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protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    HttpServletRequest processedRequest = request;
    HandlerExecutionChain mappedHandler = null;
    int interceptorIndex = -1;

    // Expose current LocaleResolver and request as LocaleContext.
    LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
    LocaleContextHolder.setLocaleContext(buildLocaleContext(request), this.threadContextInheritable);

    // Expose current RequestAttributes to current thread.
    RequestAttributes previousRequestAttributes = RequestContextHolder.getRequestAttributes();
    ServletRequestAttributes requestAttributes = new ServletRequestAttributes(request);
    RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable);

    if (logger.isTraceEnabled()) {
        logger.trace("Bound request context to thread: " + request);
    }

    try {
        ModelAndView mv = null;
        boolean errorView = false;

        try {
            processedRequest = checkMultipart(request);//检查是否是multipartrequest请求，如果是，就形成将request封装为multipartrequest，如果不是就返回原request

            // Determine handler for the current request.
            mappedHandler = getHandler(processedRequest, false);//通过handlermapping得到mappedhandler
            if (mappedHandler == null || mappedHandler.getHandler() == null) {
                noHandlerFound(processedRequest, response);
                return;
            }

            // Apply preHandle methods of registered interceptors.执行拦截器的prehandle方法。
            HandlerInterceptor[] interceptors = mappedHandler.getInterceptors();
            if (interceptors != null) {
                for (int i = 0; i < interceptors.length; i++) {
                    HandlerInterceptor interceptor = interceptors[i];
                    if (!interceptor.preHandle(processedRequest, response, mappedHandler.getHandler())) {
                        triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);
                        return;
                    }
                    interceptorIndex = i;
                }
            }

            // Actually invoke the handler.得到handleradapter
            HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
            mv = ha.handle(processedRequest, response, mappedHandler.getHandler());//执行相关操作

            // Do we need view name translation?
            if (mv != null && !mv.hasView()) {
                mv.setViewName(getDefaultViewName(request));
            }

            // Apply postHandle methods of registered interceptors.执行拦截器的posthandle方法。
            if (interceptors != null) {
                for (int i = interceptors.length - 1; i >= 0; i--) {
                    HandlerInterceptor interceptor = interceptors[i];
                    interceptor.postHandle(processedRequest, response, mappedHandler.getHandler(), mv);
                }
            }
        }
        catch (ModelAndViewDefiningException ex) {
            logger.debug("ModelAndViewDefiningException encountered", ex);
            mv = ex.getModelAndView();
        }
        catch (Exception ex) {
            Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
            mv = processHandlerException(processedRequest, response, handler, ex);
            errorView = (mv != null);
        }

        // Did the handler return a view to render?//渲染视图
        if (mv != null && !mv.wasCleared()) {
            render(mv, processedRequest, response);
            if (errorView) {
                WebUtils.clearErrorRequestAttributes(request);
            }
        }
        else {
            if (logger.isDebugEnabled()) {
                logger.debug("Null ModelAndView returned to DispatcherServlet with name '" +
                        getServletName() + "': assuming HandlerAdapter completed request handling");
            }
        }

        // Trigger after-completion for successful outcome.
        triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);//执行拦截器的AfterCompletion方法。
    }

    catch (Exception ex) {
        // Trigger after-completion for thrown exception.
        triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex);
        throw ex;
    }
    catch (Error err) {
        ServletException ex = new NestedServletException("Handler processing failed", err);
        // Trigger after-completion for thrown exception.
        triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex);
        throw ex;
    }

    finally {
        // Clean up any resources used by a multipart request.
        if (processedRequest != request) {
            cleanupMultipart(processedRequest);
        }

        // Reset thread-bound context.
        RequestContextHolder.setRequestAttributes(previousRequestAttributes, this.threadContextInheritable);
        LocaleContextHolder.setLocaleContext(previousLocaleContext, this.threadContextInheritable);

        // Clear request attributes.
        requestAttributes.requestCompleted();
        if (logger.isTraceEnabled()) {
            logger.trace("Cleared thread-bound request context: " + request);
        }
    }
}