生成指定长度的随机字符串

/**
     * 生成指定长度的随机字符串
     * 
     * @param length
     * @return
     */
    private String generateLenString(int length) {
        char[] cResult = new char[length];
        int[] flag = { 0, 0, 0 }; // A-Z, a-z, 0-9
        int i = 0;
        while (flag[0] == 0 || flag[1] == 0 || flag[2] == 0 || i < length) {
            i = i % length;
            int f = (int) (Math.random() * 3 % 3);
            if (f == 0)
                cResult[i] = (char) ('A' + Math.random() * 26);
            else if (f == 1)
                cResult[i] = (char) ('a' + Math.random() * 26);
            else
                cResult[i] = (char) ('0' + Math.random() * 10);
            flag[f] = 1;
            i++;
        }
        return new String(cResult);
    }