FrameworkServlet.processRequest() 中为什么要获取上个请求的RequestAttributes？

Question

springmvc中的FrameworkServlet的processRequest方法中为什么要先获取上一个请求保存的LocaleContext和RequestAttributes，最后在finally中还要还原LocaleContext和RequestAttributes？这么做有什么意义？

附上源码和疑点注释：

//org.springframework.web.servlet.FrameworkServlet#processRequest

protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        long startTime = System.currentTimeMillis();
        Throwable failureCause = null;


        //获取上一个请求保存的LocaleContext
        LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
        //建立新的LocaleContext
        LocaleContext localeContext = buildLocaleContext(request);
        //获取上一个请求保存的RequestAttributes
        RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
        //建立新的RequestAttributes
        ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);



        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
        asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());

        initContextHolders(request, localeContext, requestAttributes);

        try {
            doService(request, response);
        }
        catch (ServletException ex) {
            failureCause = ex;
            throw ex;
        }
        catch (IOException ex) {
            failureCause = ex;
            throw ex;
        }
        catch (Throwable ex) {
            failureCause = ex;
            throw new NestedServletException("Request processing failed", ex);
        }

        finally {
            //恢复previousLocaleContext和previousAttributes
            resetContextHolders(request, previousLocaleContext, previousAttributes);
            if (requestAttributes != null) {
                requestAttributes.requestCompleted();
            }

            if (logger.isDebugEnabled()) {
                if (failureCause != null) {
                    this.logger.debug("Could not complete request", failureCause);
                }
                else {
                    if (asyncManager.isConcurrentHandlingStarted()) {
                        logger.debug("Leaving response open for concurrent processing");
                    }
                    else {
                        this.logger.debug("Successfully completed request");
                    }
                }
            }

            publishRequestHandledEvent(request, response, startTime, failureCause);
        }
    }