code: public static String generateCharsSymbolsString(int lenght) {
          StringBuffer buf = new StringBuffer(lenght);
          SecureRandom rand = new SecureRandom();
          for (int i = 0; i < lenght; i++) {
              buf.append(charsSymbols[rand.nextInt(charsSymbols.length)]);
          }
          return buf.toString();
      }
docs: Generates random string that contains chars (a-z, A-Z) and some symbols(_,-,#,=).
  
  @param lenght the length of the generated string
  @return random string