docs: protected static boolean isValidFilename(String filename) {
  		if (filename == null || filename.length() == 0) {
  			throw new NullPointerException("文件名不能为空.");
  		}
  		if (filename.indexOf("..") != -1) {
  			throw new IllegalArgumentException("文件名称不能包含'..'");
  		}
  		Matcher m = FILENAME_PATTERN.matcher(filename);
  		return m.matches();
  	}