PHP生成短信验证码

简单版本

<?php
 function generate_code($length = 6) {
    $min = pow(10 , ($length - 1));
    $max = pow(10, $length) - 1;
    return rand($min, $max);
 }

复杂版本（java）

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;
 }