public URLNormalizer addWWW() {
        String host = toURL().getHost();
        if (!host.toLowerCase().startsWith("www.")) {
            url = StringUtils.replaceOnce(url, host, "www." + host);
        }
        return this;
    }
@Test
    public void testAddWWW() {
        s = "http://example.com/foo.html";
        t = "http://www.example.com/foo.html";
        assertEquals(t, n(s).addWWW().toString());
        s = "http://wwwexample.com/foo.html";
        t = "http://www.wwwexample.com/foo.html";
        assertEquals(t, n(s).addWWW().toString());
        s = "http://www.example.com/foo.html";
        t = "http://www.example.com/foo.html";
        assertEquals(t, n(s).addWWW().toString());
    }