java InetAddress.getLocalHost(); returns 127.0.0.1 ... how to get REAL IP?

Question

I'm writing a simple networking app. I need to know the real IP of my machine on the network, like 192.168.1.3 . getLocalHost returns 127.0.0.1 (on Linux, I don't know if it is the same on windows). How to do it?

Answer 1

If you actually want to work with all of the IP addresses on the machine you can get those with the NetworkInterface class. Of course, then you need to which one you actually want to use, but that's going to be different depending on what you're using it for, or you might need to expand the way you're using it to account for multiple addresses.

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

public class ShowInterfaces
{
        public static void main(String[] args) throws Exception
        {
                System.out.println("Host addr: " + InetAddress.getLocalHost().getHostAddress());  // often returns "127.0.0.1"
                Enumeration<NetworkInterface> n = NetworkInterface.getNetworkInterfaces();
                for (; n.hasMoreElements();)
                {
                        NetworkInterface e = n.nextElement();
                        System.out.println("Interface: " + e.getName());
                        Enumeration<InetAddress> a = e.getInetAddresses();
                        for (; a.hasMoreElements();)
                        {
                                InetAddress addr = a.nextElement();
                                System.out.println("  " + addr.getHostAddress());
                        }
                }
        }
}

Answer 2

As the machine might have multiple addresses, it's hard to determine which one is the one for you. Normally, you want the system to assign an IP based on its routing table. As the result depends on the IP you'd like to connect to, there is a simple trick: Simply create a connection and see what address you've got from the OS:

// output on my machine: "192.168.1.102"
Socket s = new Socket("192.168.1.1", 80);
System.out.println(s.getLocalAddress().getHostAddress());
s.close();

// output on my machine: "127.0.1.1"
System.out.println(InetAddress.getLocalHost().getHostAddress());

I'm not sure whether it's possible to do this without establishing a connection though. I think I've once managed to do it with Perl (or C?), but don't ask me about Java. I think it might be possible to create a UDP socket (DatagramSocket) without actually connecting it.

If there is a NAT router on the way you won't be able to get the IP that remote hosts will see though. However, as you gave 192.* as an example, I think you don't care.

Answer 3

To fix it:

1. Find your host name. Type: hostname. For example, you find your hostname is mycomputer.xzy.com

2. Put your host name in your hosts file. /etc/hosts . Such as

   10.50.16.136 mycomputer.xzy.com
   

Answer 4

Here is a way to avoid IPv6 and Loopback results.

public InetAddress getCurrentIp() {
            try {
                Enumeration<NetworkInterface> networkInterfaces = NetworkInterface
                        .getNetworkInterfaces();
                while (networkInterfaces.hasMoreElements()) {
                    NetworkInterface ni = (NetworkInterface) networkInterfaces
                            .nextElement();
                    Enumeration<InetAddress> nias = ni.getInetAddresses();
                    while(nias.hasMoreElements()) {
                        InetAddress ia= (InetAddress) nias.nextElement();
                        if (!ia.isLinkLocalAddress() 
                         && !ia.isLoopbackAddress()
                         && ia instanceof Inet4Address) {
                            return ia;
                        }
                    }
                }
            } catch (SocketException e) {
                LOG.error("unable to get current IP " + e.getMessage(), e);
            }
            return null;
        }

Answer 5

I wrote this code:

import java.net.InterfaceAddress;
import java.net.NetworkInterface;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;


private String[] getHostAddresses() {
  Set<String> HostAddresses = new HashSet<>();
  try {
    for (NetworkInterface ni : Collections.list(NetworkInterface.getNetworkInterfaces())) {
      if (!ni.isLoopback() && ni.isUp() && ni.getHardwareAddress() != null) {
        for (InterfaceAddress ia : ni.getInterfaceAddresses()) {
          if (ia.getBroadcast() != null) {  //If limited to IPV4
            HostAddresses.add(ia.getAddress().getHostAddress());
          }
        }
      }
    }
  } catch (SocketException e) { }
  return HostAddresses.toArray(new String[0]);
}

Check it!

For me:

• Must be not LoopBack!
• Must be UP!
• Must have MAC Address (is not null)

Answer 6

Your computer may have multiple IPs. How do you know which one? The way I do it is to have a very simple CGI running on another machine that reports back the IP it's seen, and I hit that when I need to know what my IP looks like to the outside world.

Answer 7

Instead of using InetAddress.getHostAddress(), I call the getHost4Address routine that I wrote to get the first non-loopback address...

/**
 * Returns this host's non-loopback IPv4 addresses.
 * 
 * @return
 * @throws SocketException 
 */
private static List<Inet4Address> getInet4Addresses() throws SocketException {
    List<Inet4Address> ret = new ArrayList<Inet4Address>();

    Enumeration<NetworkInterface> nets = NetworkInterface.getNetworkInterfaces();
    for (NetworkInterface netint : Collections.list(nets)) {
        Enumeration<InetAddress> inetAddresses = netint.getInetAddresses();
        for (InetAddress inetAddress : Collections.list(inetAddresses)) {
            if (inetAddress instanceof Inet4Address && !inetAddress.isLoopbackAddress()) {
                ret.add((Inet4Address)inetAddress);
            }
        }
    }

    return ret;
}

/**
 * Returns this host's first non-loopback IPv4 address string in textual
 * representation.
 * 
 * @return
 * @throws SocketException
 */
private static String getHost4Address() throws SocketException {
    List<Inet4Address> inet4 = getInet4Addresses();
    return !inet4.isEmpty()
            ? inet4.get(0).getHostAddress()
            : null;
}

Answer 8

Get the current request from the current instance

HttpServletRequest httpServletRequest = (HttpServletRequest) FacesContext.getCurrentInstance().getExternalContext().getRequest();

then get the address from the request

ip = httpServletRequest.getRemoteAddr();

Answer 9

Get the ip address of the current box matching a pattern:

import java.io.*; 
import java.util.*; 
import java.util.regex.Pattern; 

String ipPattern = "(192.1.200.)(\\d){1,3}";      //your organization pattern 
try{ 
    Enumeration en = NetworkInterface.getNetworkInterfaces(); 
    while (en.hasMoreElements()) { 
        NetworkInterface ni = (NetworkInterface) en.nextElement(); 
        Enumeration ee = ni.getInetAddresses(); 
        while (ee.hasMoreElements()) { 
            InetAddress ia = (InetAddress) ee.nextElement(); 
            String ip = ia.getHostAddress(); 
            System.out.println("ip: '" + ip + "'\n"); 
            boolean matched = Pattern.matches(ipPattern, ip); 
            if (matched) { 
                System.out.println("matched\n"); 
            }
        } 
    } 
} 
catch(Exception e){ } 

Result:

ip: 'fe80:0:0:0:510a:528b:7204:39d0%enp0s25'
ip: '192.1.200.3'
matched
ip: '0:0:0:0:0:0:0:1%lo'
ip: '127.0.0.1'

Answer 10

In case you want to get the IP address of your PC, you have to use the "InetAddress" object, which exists in "java.net.InetAddress" library.

The following method returns your IP:

public String getIp() {

    String myIp = "";
    InetAddress ip;

    try {
        ip = InetAddress.getLocalHost();
        myIp = ip.getHostAddress();      // This method returns the IP.
    } catch (UnknownHostException e) {
        e.printStackTrace();
    }

    return myIp;
}