private boolean
findProperty() {
	String prop;
	List lserver = new ArrayList(0);
	List lsearch = new ArrayList(0);

	// add dns server in Google
	addServer("8.8.8.8", lserver);
	//StringTokenizer st;

	//prop = System.getProperty("dns.server");
	//if (prop != null) {
	//	st = new StringTokenizer(prop, ",");
	//	while (st.hasMoreTokens())
	//		addServer(st.nextToken(), lserver);
	//}

	//prop = System.getProperty("dns.search");
	//if (prop != null) {
	//	st = new StringTokenizer(prop, ",");
	//	while (st.hasMoreTokens())
	//		addSearch(st.nextToken(), lsearch);
	//}
	configureFromLists(lserver, lsearch);
	return (servers != null && searchlist != null);
}
Looks in the system properties to find servers and a search path.
Servers are defined by dns.server=server1,server2...
The search path is defined by dns.search=domain1,domain2...
src/main/java/core/org/xbill/DNS/ResolverConfig.java