How to Retrieve the Current Machine's IP Address in Java?

Question

How to retrieve the current machine's IP address in Java?

public class IPAddressRetriever {
    public static void main(String[] args) throws Exception {
        enumerationNetworkInterfaces();
    }

    public static void enumerationNetworkInterfaces() throws Exception {
        Enumeration<NetworkInterface> networkInterfaces = NetworkInterface.getNetworkInterfaces();
        while (networkInterfaces.hasMoreElements()) {
            NetworkInterface networkInterface = networkInterfaces.nextElement();
            Enumeration<InetAddress> inetAddresses = networkInterface.getInetAddresses();
            while (inetAddresses.hasMoreElements()) {
                InetAddress inetAddress = inetAddresses.nextElement();
                System.out.println(inetAddress.getHostAddress());
            }
        }
    }
}

Answer

Retrieving the current machine's IP address in Java can be essential for networking applications. This guide will help you distinguish between local and public IP addresses for various use cases.

import java.net.*;
import java.util.*;

public class IPAddressRetriever {
    public static void main(String[] args) throws Exception {
        enumerationNetworkInterfaces();
    }

    public static void enumerationNetworkInterfaces() throws Exception {
        Enumeration<NetworkInterface> networkInterfaces = NetworkInterface.getNetworkInterfaces();
        while (networkInterfaces.hasMoreElements()) {
            NetworkInterface networkInterface = networkInterfaces.nextElement();
            Enumeration<InetAddress> inetAddresses = networkInterface.getInetAddresses();
            while (inetAddresses.hasMoreElements()) {
                InetAddress inetAddress = inetAddresses.nextElement();
                String ip = inetAddress.getHostAddress();
                // Check if it's a loopback address or a private address
                if (inetAddress.isLoopbackAddress()) {
                    System.out.println("Loopback IP: " + ip);
                } else if (inetAddress instanceof Inet4Address && !networkInterface.isVirtual()) {
                    System.out.println("Public or LAN IP: " + ip);
                }
            }
        }
    }
}

Causes

Local IP addresses are often returned instead of public IPs by default methods.
Multiple network interfaces can be present on a machine, complicating IP retrieval.

Solutions

Use the `NetworkInterface` class to enumerate all network interfaces and their associated IP addresses.
Identify the desired IP address based on your criteria (PPP, LAN, or localhost).

Common Mistakes

Mistake: Assuming InetAddress.getLocalHost() will always return the public IP address.

Solution: Use NetworkInterface.getNetworkInterfaces() to get all network interfaces and filter by desired IP type.

Mistake: Not distinguishing between local and public IPs.

Solution: Explicitly check networkInterface.isVirtual() and address types such as isLoopbackAddress() for filtering.

Helpers

Java IP address retrieval
get machine IP address Java
NetworkInterface Java
public and local IP in Java
Socket connection Java