How to get domain name from incoming hit to my java web app

Question

• I believe, someone out there can solve my problem. I have developed web Java App, this app will process the request base on domain name, the case as follows: (not real domain) www.salesdept.com www.inventory.com www.maintenance.com www.office.com, all of above domain will redirect to my server Java web app

  // after googling, I found a code as follows:

  public static String getDomainName(String url) throws URISyntaxException {
  URI uri = new URI(url);
  String domain = uri.getHost();
  return domain.startsWith("www.") ? domain.substring(4) : domain;
  }
  

  // As we can see, String url needs to specify the value.

Question: How to do it in Java to catch the domain name programatically from incoming hit to my web app?, honestly, I dont have idea how to do it.