Java random generation of SMS verification code method

This article illustrates the method of Java random generation of SMS verification code. Share with you for your reference, as follows:

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;
}

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