code: public static void lookupHostname(ErrorReporter errorReporter) {
          String myHostName = getProperty(PROPERTY_LOGSTASH_GELF_HOSTNAME, "unknown");
          String myFQDNHostName = getProperty(PROPERTY_LOGSTASH_GELF_FQDN_HOSTNAME, "unknown");
          String myAddress = "";
  
          if (!Boolean.parseBoolean(getProperty(PROPERTY_LOGSTASH_GELF_SKIP_HOSTNAME_RESOLUTION, "false"))) {
  
              try {
  
                  String resolutionOrder = getProperty(PROPERTY_LOGSTASH_GELF_HOSTNAME_RESOLUTION_ORDER,
                          RESOLUTION_ORDER_NETWORK_LOCALHOST_FALLBACK);
  
                  InetAddress inetAddress = null;
                  if (resolutionOrder.equals(RESOLUTION_ORDER_NETWORK_LOCALHOST_FALLBACK)) {
                      inetAddress = getInetAddressWithHostname();
                  }
  
                  if (resolutionOrder.equals(RESOLUTION_ORDER_LOCALHOST_NETWORK_FALLBACK)) {
                      if (isQualified(InetAddress.getLocalHost())) {
                          inetAddress = InetAddress.getLocalHost();
                      } else {
                          inetAddress = getInetAddressWithHostname();
                      }
                  }
  
                  if (inetAddress == null) {
                      inetAddress = InetAddress.getLocalHost();
                  }
  
                  myHostName = getHostname(inetAddress, false);
                  myFQDNHostName = getHostname(inetAddress, true);
                  myAddress = inetAddress.getHostAddress();
              } catch (IOException e) {
                  errorReporter.reportError("Cannot resolve hostname", e);
              }
          }
  
          FQDN_HOSTNAME = myFQDNHostName;
          HOSTNAME = myHostName;
          ADDRESS = myAddress;
      }
docs: Triggers the hostname lookup.
  @param errorReporter the error reporter