生成订单号

	public static BigInteger generateRandom(int length) {
	    Random random = new Random();
	    char[] digits = new char[length];
	    digits[0] = (char) (random.nextInt(9) + '1');
	    for (int i = 1; i < length; i++) {
	        digits[i] = (char) (random.nextInt(10) + '0');
	    }
	    return new BigInteger(new String(digits));
	}