code: public static String parent(String file) {
        if (StringUtils.isNullOrBlank(file)) {
           return StringUtils.EMPTY;
        }
        file = StringUtils.trim(file);
        String path = path(file);
        int index = indexOfLastSeparator(path);
        if (index <= 0) {
           return SystemInfo.isUnix() ? Character.toString(UNIX_SEPARATOR) : Character.toString(WINDOWS_SEPARATOR);
        }
        return path.substring(0, index);
     }
docs: Returns the parent directory for the given file. If the file passed in is actually a directory it will get the
  directory's parent.
  
  @param file The file
  @return The parent or null if the file is null or empty