code: public void changeGroup(String group, String file)
          throws IOException, ServerException {
          String arguments = group + " " + file;
          Command cmd = new Command("SITE CHGRP", arguments);
          try {
              controlChannel.execute(cmd);
          } catch (UnexpectedReplyCodeException urce) {
              throw ServerException.embedUnexpectedReplyCodeException(urce);
          } catch (FTPReplyParseException rpe) {
              throw ServerException.embedFTPReplyParseException(rpe);
          }
      }
docs: Change the Unix group membership of a file.
  
  @param group the name or ID of the group
  @param file the file whose group membership should be changed
  @exception ServerException if an error occurred.