code: @WebOperationMethod
      public Map<String,Object> download(Map<String, Object> params, HttpServletRequest request, HttpServletResponse response) throws Exception {
          String database = Objects.get(params, "database");
          String collection = Objects.get(params, "collection", COLLECTION);
          String id = Objects.get(params, "id");
  
          FileStorage.FileReadBean b = null;
          try{
              b = FileStorage.read(new Id(database,collection,id));
              response.setContentType(b.getMeta().getContentType());
              try {
                  IOUtils.copy(b.getInputStream(), response.getOutputStream());
              } catch (IOException e) {
                  throw S1SystemError.wrap(e);
              }
          }catch (NotFoundException e) {
              response.setStatus(404);
          }finally {
              FileStorage.closeAfterRead(b);
          }
          return null;
      }
docs: Download file
  
  @param params   {group:"...default is GROUP...", id:"..."}
  @param response