how to fetch base url from the given url using java

I am trying to fetch base URL using java. I have used jtidy parser in my code to fetch the title. I am getting the title properly using jtidy, but I am not getting the base url from the given URL.

I have some URL as input:

String s1 = "http://staff.unak.is/andy/GameProgramming0910/new_page_2.htm";
String s2 = "http://www.complex.com/pop-culture/2011/04/10-hottest-women-in-fast-and-furious-movies";

From the first string, I want to fetch "http://staff.unak.is/andy/GameProgramming0910/" as a base URL and from the second string, I want "http://www.complex.com/" as a base URL.

I am using code:

URL url = new URL(s1);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
InputStream in = conn.getInputStream();
Document doc = new Tidy().parseDOM(in, null);
String titleText = doc.getElementsByTagName("title").item(0).getFirstChild()
.getNodeValue();

I am getting titletext, but please can let me know how to get base URL from above given URL?