Android :: Need To Display Android Downloading Progress?

I'm writing a function to download file:
URL _url = new URL("http://kevin95800.free.fr/Music/Jay%20Sean%20-%20Down%20(ft.%20Lil%20Wayne).mp3");
URLConnection conn = _url.openConnection();
conn.connect();
throw new RuntimeException("stream is null");}
byte buf[] = new byte[128];
do
{int numread = is.read(buf);Log.i("html2" , numread+" ");
if(numread <=0)
break;
fos.write(buf , 0 , numread);}while(true);.close();
My question is , how do i know the total byte of the file i'm downloading? because , i wanna display the downloading progress. could someone teach me