Java随机生成手机短信验证码的方法

/*** 创建指定数量的随机字符串* @param numberFlag 是否是数字* @param length* @return*/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;}