lotto 당첨번호 파싱

try {
   for(int i=340;;i++) {
    URL url = new URL("http://www.645lotto.net/Confirm/number.asp?sltSeq="+i);
    Reader r = new InputStreamReader(url.openStream());
    BufferedReader br = new BufferedReader(r);
   
    String prefix = "<img src=\"../images/Comm/s";
    String number  = "";
    String t;
    while((t = br.readLine()) != null) {
     if(t.indexOf(prefix) > -1) {
      String num = t.trim().substring(prefix.length(), prefix.length() + 2);
      if(!num.equals("pl")) number += (number.equals("") ? "" : ",") + num;
     }
    }
    if(number.equals("")) break;
    System.out.println(i + " -> " + number);
   }
  } catch (Exception e) {
   e.printStackTrace();
  }