Since you are using embedded Jetty (not running it in Jetty) so you should put your configuration file on the classpath i.e src/main/resources, which is a standard Maven location.
According to this tutorial you should then load the resource file and initialize Jetty with it:
public class FileServerXml
{
public static void main(String[] args) throws Exception
{
Resource fileserver_xml = Resource.newSystemResource("fileserver.xml");
XmlConfiguration configuration = new XmlConfiguration(fileserver_xml.getInputStream());
Server server = (Server)configuration.configure();
server.start();
server.join();
}
}
The example is for a file server but I imagine it is similar for any other.