The following uses Amazon web services and works for me.
import java.net.*;
import java.io.*;
public class IPTest{
public static void main(String args[]) throws Exception{
URL whatismyip = new URL("http://checkip.amazonaws.com/");
BufferedReader in = new BufferedReader(new InputStreamReader(
whatismyip.openStream()));
String ip = in.readLine(); //you get the IP as a String
System.out.println("My IP address:"+ip);
}
}