code: protected String generateToken() {
          StringBuilder sb = new StringBuilder();
          for (int i = 0; i < TOKEN_MIDDLE_LEN; i++) {
              sb.append(TOKEN_DICT.charAt(random.nextInt(TOKEN_DICT.length())));
          }
          return TOKEN_PREFIX + sb.toString() + TOKEN_SUFFIX;
      }
docs: Generate a new token used in describeInstanceResponse while paging enabled.
  
  @return a random string as a token