import com.google.common.net.InternetDomainName;

public static void main(String[] args) {    InternetDomainName top =         InternetDomainName.from("keyupgrade.spaceforupdate.download").topPrivateDomain();    System.out.println(top);  }

比如我写的：

private String extractDomain(String domain) {        try {            return InternetDomainName.from(domain).topPrivateDomain().name();        } catch (java.lang.IllegalStateException e) {            String[] levels = domain.split("\\.");//            if (levels.length > 1) {//                return levels[levels.length - 2] + "." + levels[levels.length - 1];//            } else {
                    return levels[levels.length-1];//            }        } catch (java.lang.IllegalArgumentException e){            String[] levels = domain.split("\\.");            return levels[levels.length-1];        }    }

参考：

https://stackoverflow.com/questions/45046265/internetdomainname-and-publicsuffix-list

https://github.com/google/guava/blob/master/guava/src/com/google/common/net/InternetDomainName.java

https://stackoverflow.com/questions/7217271/extract-main-domain-name-from-a-given-url