创建指定数量的随机字符串的工具类

第一种：随机生成n位数字做验证码

public class RandomCodeUtil
{
  public static String getRandomNumber(int length)
  {
    String result = "";
    for (int i = 0; i < length; i++) {
      result = result + (int)(Math.random() * 9.0D);
    }
    return result;
  }
}

第二种：创建指定数量的随机字符串

/**
     * 创建指定数量的随机字符串
     * @param numberFlag 是否是纯数字
     * @param length 随机数位数
     * @return String
     */
    public  static String createRandom(boolean numberFlag, int length){
        String retStr = "";
        String strTable = numberFlag ? "1234567890" : "1234567890abcdefghijkmnpqrstuvwxyz";
        int len = strTable.length();
        boolean bDone = true;
        do {
            retStr = "";
            int count = 0;
            for (int i = 0; i < length; i++) {
                double dblR = Math.random() * len;
                int intR = (int) Math.floor(dblR);
                char c = strTable.charAt(intR);
                if (('0' <= c) && (c <= '9')) {
                    count++;
                }
                retStr += strTable.charAt(intR);
            }
            if (count >= 2) {
                bDone = false;
            }
        } while (bDone);
        return retStr;
    }