/**
  * 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;
 }