code: public Collection getUploadFileID(HttpServletRequest request) {
      Collection set = null;
      Debug.logVerbose("[JdonFramework]--> enter session filter ", module);
      try {
         //保证一个id只有一个
  
        //从下一个Filter取出ID集合，没有重复
        Collection list = imageFilter.getUploadFileID(request);
        if (list == null)
          set = new LinkedHashSet();
        else
          set = new LinkedHashSet(list);
  
        HttpSession session = request.getSession();
        Collection sessionList = (Collection) session.getAttribute(PIC_NAME_PACKAGE);
        if (sessionList == null) return set;
  
        //确保Session中的ID覆盖下一个Filter中ID
        Iterator  iter = sessionList.iterator();
        while (iter.hasNext()) {
          UploadFile uploadFile = (UploadFile) iter.next();
          if ( (uploadFile.getId() != null) && (!uploadFile.getId().equals(""))) {
            set.add(uploadFile.getId());
          } else { //如果Session有多于下一个Filter的ID，以排列TempId加入
            set.add(uploadFile.getTempId());
          }
        }
      } catch (Exception ex) {
        Debug.logError("[JdonFramework] getUploadFileID error" + ex, module);
      }
      return set;
  
    }
docs: 将HttpSession中的ID集合和老的imageFilterID集合合并
  
  保证每个ID只有一个。
  
  @param request
  @return