Mock DNS Server in Java - application code

LookupUtil.java

import org.xbill.DNS.Lookup;
import org.xbill.DNS.Name;
import org.xbill.DNS.Record;
import org.xbill.DNS.Resolver;
import org.xbill.DNS.TextParseException;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class LookupUtil {
    

    public static List<String> forNameType(Resolver resolver, String nameStr, int type) {
        Name name;

        try {
            name = Name.fromString(nameStr);
        } catch (TextParseException e) {
            throw new IllegalArgumentException();
        }
        Lookup lookup = new Lookup(name, type);
        lookup.setResolver(resolver);
        lookup.setCache(null);
        lookup.run();

        if (lookup.getResult() != Lookup.SUCCESSFUL) {
            throw new RuntimeException(lookup.getErrorString());
        }
        return Arrays.stream(lookup.getAnswers())
                .map(Record::rdataToString)
                .collect(Collectors.toList());
    }
}