code: package io.ray.runtime.util;
  
  import com.google.common.base.Strings;
  import java.net.Inet6Address;
  import java.net.InetAddress;
  import java.net.NetworkInterface;
  import java.util.Enumeration;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  public class NetworkUtil {
  
    private static final Logger LOGGER = LoggerFactory.getLogger(NetworkUtil.class);
  
    public static String getIpAddress(String interfaceName) {
      try {
        Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
        while (interfaces.hasMoreElements()) {
          NetworkInterface current = interfaces.nextElement();
          if (!current.isUp() || current.isLoopback() || current.isVirtual()) {
            continue;
          }
          if (!Strings.isNullOrEmpty(interfaceName)
              && !interfaceName.equals(current.getDisplayName())) {
            continue;
          }
          Enumeration<InetAddress> addresses = current.getInetAddresses();
          while (addresses.hasMoreElements()) {
            InetAddress addr = addresses.nextElement();
            if (addr.isLoopbackAddress()) {
              continue;
            }
            if (addr instanceof Inet6Address) {
              continue;
            }
            return addr.getHostAddress();
          }
        }
        LOGGER.warn("You need to correctly specify [ray.java] net_interface in config.");
      } catch (Exception e) {
        LOGGER.error("Can't get ip address, use 127.0.0.1 as default.", e);
      }
  
      return "127.0.0.1";
    }
  
    public static String localhostIp() {
      return "127.0.0.1";
    }
  }
  