URL에서 domain 가져오기

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class DomainUrlUtils {
    private static String[] TLD = {"com", "net"}; // top-level domain
    private static String[] SLD = {"co\\.kr"}; // second-level domain

    /**
     * 도메인 가져오기
     * 주의: 새로운 top-level, second-level이 있다면 TLD, SLD에 추가할 것
     *
     * @param url
     * @return domain
     */
    public static String getDomainName(String url) {
        Pattern pattern = Pattern.compile("(?<=)[^(\\.|\\/)]\\w+\\.(" + joinTldAndSld("|") + ")$");
        Matcher match = pattern.matcher(url);

        return match.find() ? match.group() : null;
    }

    /**
     * TLD, SLD를 delimiter로 이어주기
     *
     * @param delimiter
     * @return
     */
    private static String joinTldAndSld(String delimiter) {
        String t = String.join(delimiter, TLD);
        String s = String.join(delimiter, SLD);

        return new StringBuilder(t).append(s.isEmpty() ? "" : "|" + s).toString();
    }
}

public class DomainUrlUtilsTest {

    @Test
    public void getDomainName() throws Exception {
        // given
        String[][] domainUrls = {
            {
                "test.com",
                "sub1.test.com",
                "sub1.sub2.test.com",
                "https://sub1.test.com",
                "http://sub1.sub2.test.com"
            },
            {
                "https://domain.com",
                "https://sub.domain.com"
            },
            {
                "http://domain.co.kr",
                "http://sub.domain.co.kr",
                "http://local.sub.domain.co.kr",
                "http://local-test.sub.domain.co.kr",
                "sub.domain.co.kr",
                "domain.co.kr",
                "test.sub.domain.co.kr"
            }
        };

        String[] expectedUrls = {
            "test.com",
            "domain.com",
            "domain.co.kr"
        };

        // when
        // then
        for (int domainIndex = 0; domainIndex < domainUrls.length; domainIndex++) {
            for (String url : domainUrls[domainIndex]) {
                String convertedUrl = DomainUrlUtils.getDomainName(url);

                if (expectedUrls[domainIndex].equals(convertedUrl)) {
                    System.out.println(url + " -> " + convertedUrl);
                } else {
                    Assert.fail("origin Url: " + url + " / converted Url: " + convertedUrl);
                }
            }
        }
    }
}

test.com -> test.com
sub1.test.com -> test.com
sub1.sub2.test.com -> test.com
https://sub1.test.com -> test.com
http://sub1.sub2.test.com -> test.com
https://domain.com -> domain.com
https://sub.domain.com -> domain.com
http://domain.co.kr -> domain.co.kr
http://sub.domain.co.kr -> domain.co.kr
http://local.sub.domain.co.kr -> domain.co.kr
http://local-test.sub.domain.co.kr -> domain.co.kr
sub.domain.co.kr -> domain.co.kr