public static String getRandomString(int length) {
        length = length < 0 ? -length : length;
        char[] chs = new char[length];
        Random ran = new Random();
        for(int i = 0; i < chs.length; i++) {
            chs[i] = (char)(ran.nextInt(10) + '0');
        }
        return new String(chs);
    }

------解决方案--------------------
Java code

  /**
     * 返回一个随机数
     *
     * @param i
     * @return 一个随机数
     */
    public static String getRandom(int i) {
        Random random = new Random();

        // int suiJiShu = jjj.nextInt(9);
        if (i == 0) {
            return "";
        }

        String strRandom = "";

        for (int k = 0; k < i; k++) {
            strRandom = strRandom + random.nextInt(9);
        }

        return strRandom;
    }