public static String randomNumeric(int length) {
        int leftLimit = 48; // letter '0'
        int rightLimit = 57; // letter '9'
        Random random = new Random();

        return random.ints(leftLimit, rightLimit + 1)
                .limit(length)
                .collect(StringBuilder::new, StringBuilder::appendCodePoint, StringBuilder::append)
                .toString();
    }
@Test
    public void testNumeric() {
        System.out.println(ByteUtil.randomNumeric(100));
    }