code: private String[] expandAtFiles(String args[]) throws CmdLineException {
          List<String> result = new ArrayList<String>();
          for (String arg : args) {
              if (arg.startsWith("@")) {
                  File file = new File(arg.substring(1));
                  if (!file.exists())
                      throw new CmdLineException(this,Messages.NO_SUCH_FILE,file.getPath());
                  try {
                      result.addAll(readAllLines(file));
                  } catch (IOException ex) {
                      throw new CmdLineException(this, "Failed to parse "+file,ex);
                  }
              } else {
                  result.add(arg);
              }
          }
          return result.toArray(new String[result.size()]);
      }
docs: Expands every entry prefixed with the AT sign by
  reading the file. The AT sign is used to reference
  another file that contains command line options separated
  by line breaks.
  @param args the command line arguments to be preprocessed.
  @return args with the @ sequences replaced by the text files referenced
  by the @ sequences, split around the line breaks.
  @throws CmdLineException