很清楚，我也把FileUploadStatus这个Bean存取于Session中。

        Servlet实现：BackGroundService这个Servlet类负责接收Form Post数据、回应状态轮询请求、处理取消文件上传的请求。尽管可以把这些功能相互分离开来（比如构造一个FileUploadManager类），但出于简单明了、便于阅读之目的，还是将它们放到Servlet中，只是由不同的方法进行分割。
        {BackGroundService中的processFileUpload方法用于处理文件上传请求}：

/**
* 处理文件上传
* @param request
* @param response
* @throws IOException
* @throws ServletException
*/
private void processFileUpload(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException{
      DiskFileItemFactory factory = new DiskFileItemFactory();
      //设置内存阀值，超过后写入临时文件
      factory.setSizeThreshold(10240000);
      //设置临时文件存储位置
      factory.setRepository(new File(request.getRealPath("/upload/temp")));
      ServletFileUpload upload = new ServletFileUpload(factory);
      //设置单个文件的最大上传size
      upload.setFileSizeMax(10240000);
      //设置整个request的最大size
      upload.setSizeMax(10240000);
      upload.setProgressListener(new FileUploadListener(request.getSession()));
      //保存初始化后的FileUploadStatus Bean
        storeFileUploadStatusBean(request.getSession(),initFileUploadStatusBean(request));
                
        String forwardURL="";
        try {
             List items = upload.parseRequest(request);
             //获得返回url
               for(int i=0;i<items.size();i++){
                   FileItem item=(FileItem)items.get(i);
                   if (item.isFormField()){
                      logger.debug("form Field["+item.getFieldName()+"]="+item.getString());
                      forwardURL=item.getString();
                      break;
                                }
                        }
            //处理文件上传
              for(int i=0;i<items.size();i++){
                 FileItem item=(FileItem)items.get(i);

                   //取消上传
                 if (takeOutFileUploadStatusBean(request.getSession()).getCancel()){
                     deleteUploadedFile(request);
                     break;
                    }
                   //保存文件
                 else if (!item.isFormField() && item.getName().length()>0){
                         String fileName=takeOutFileName(item.getName());
                         logger.debug("处理文件["+fileName+"]:保存路径为"
                         +request.getRealPath(UPLOAD_DIR)+File.separator+fileName);
                         File uploadedFile =
new File(request.getRealPath(UPLOAD_DIR)+File.separator+fileName);
                         item.write(uploadedFile);
                         //更新上传文件列表
                         FileUploadStatus fUploadStatus=takeOutFileUploadStatusBean
(request.getSession());
                         fUploadStatus.getUploadFileUrlList().add(fileName);
                         storeFileUploadStatusBean(request.getSession(),fUploadStatus);
                         Thread.sleep(500);
                          }
                 }
                
       } catch (FileUploadException e) {
              logger.error("上传文件时发生错误:"+e.getMessage());
              e.printStackTrace();
              uploadExceptionHandle(request,"上传文件时发生错误:"+e.getMessage());
        } catch (Exception e) {
               // TODO Auto-generated catch block
               logger.error("保存上传文件时发生错误:"+e.getMessage());
               e.printStackTrace();
               uploadExceptionHandle(request,"保存上传文件时发生错误:"+e.getMessage());
         }
          if (forwardURL.length()==0){
             forwardURL=DEFAULT_UPLOAD_FAILURE_URL;
                }
        request.getRequestDispatcher(forwardURL).forward(request,response);
        }


        {BackGroundService中的responseFileUploadStatusPoll方法用于处理对文件上传状态的轮询请求}：

/**
* 回应上传状态查询
* @param request
* @param response
* @throws IOException
*/
private void responseFileUploadStatusPoll(HttpServletRequest request,HttpServletResponse response)
throws IOException{
response.setContentType("text/xml");
response.setCharacterEncoding("UTF-8");
response.setHeader("Cache-Control", "no-cache");
logger.debug("发送上传状态回应");
response.getWriter().write(XmlUnSerializer.serializeBean(
          request.getSession().getAttribute(UPLOAD_STATUS)));
}


        {BackGroundService中的processCancelFileUpload方法用于处理取消文件上传的请求}：

/**
* 处理取消文件上传
* @param request
* @param response
* @throws IOException
*/
private void processCancelFileUpload(HttpServletRequest request,HttpServletResponse response)
throws IOException{
FileUploadStatus fUploadStatus=(FileUploadStatus)request.getSession().getAttribute(UPLOAD_STATUS);
fUploadStatus.setCancel(true);
request.getSession().setAttribute(UPLOAD_STATUS, fUploadStatus);
responseFileUploadStatusPoll(request,response);
 }


Web客户端代码：


Prototype给开发者更多的自由选择

web客户端使用了基于Prototype的AjaxWrapper类和XMLDomForAjax类，前者实现了对Ajax.Request功能的封装，而后者实现了对来自服务器的XML Response的反序列化（反序列化为JavaScript对象）。

 

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