Please change in: com.redfin.sitemapgenerator.SitemapGenerator

in method: private void writeSiteMap(OutputStreamWriter out) throws IOException

out.write("<urlset xmlns=\"http://www.sitemaps.org/schemas/sitemap/0.9\" ");

TO:

out.write("<urlset xmlns=\"http://www.sitemaps.org/schemas/sitemap/0.9\" " + " xmlns:xsi=\"http://www.w3.org/2001/XMLSchema- instance\"" + "
xsi:schemaLocation=\"http://www.sitemaps.org/schemas/sitemap/0.9&quot; + "
http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd\"");

Could you please open a pull request with the fix at https://github.com/dfabulich/sitemapgen4j ?