Getting the 'external' IP address in Java

Question

I\'m not too sure how to go about getting the external IP address of the machine as a computer outside of a network would see it.

My following IPAddress class only g

Answer 1

One of the comments by @stivlo deserves to be an answer:

You can use the Amazon service http://checkip.amazonaws.com

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;

public class IpChecker {

    public static String getIp() throws Exception {
        URL whatismyip = new URL("http://checkip.amazonaws.com");
        BufferedReader in = null;
        try {
            in = new BufferedReader(new InputStreamReader(
                    whatismyip.openStream()));
            String ip = in.readLine();
            return ip;
        } finally {
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

Answer 2

As @Donal Fellows wrote, you have to query the network interface instead of the machine. This code from the javadocs worked for me:

The following example program lists all the network interfaces and their addresses on a machine:

import java.io.*;
import java.net.*;
import java.util.*;
import static java.lang.System.out;

public class ListNets {

    public static void main(String args[]) throws SocketException {
        Enumeration<NetworkInterface> nets = NetworkInterface.getNetworkInterfaces();
        for (NetworkInterface netint : Collections.list(nets))
            displayInterfaceInformation(netint);
    }

    static void displayInterfaceInformation(NetworkInterface netint) throws SocketException {
        out.printf("Display name: %s\n", netint.getDisplayName());
        out.printf("Name: %s\n", netint.getName());
        Enumeration<InetAddress> inetAddresses = netint.getInetAddresses();
        for (InetAddress inetAddress : Collections.list(inetAddresses)) {
            out.printf("InetAddress: %s\n", inetAddress);
        }
        out.printf("\n");
     }
} 

The following is sample output from the example program:

Display name: TCP Loopback interface
Name: lo
InetAddress: /127.0.0.1

Display name: Wireless Network Connection
Name: eth0
InetAddress: /192.0.2.0

From docs.oracle.com

Answer 3

An alternative solution is to execute an external command, obviously, this solution limits the portability of the application.

For example, for an application that runs on Windows, a PowerShell command can be executed through jPowershell, as shown in the following code:

public String getMyPublicIp() {
    // PowerShell command
    String command = "(Invoke-WebRequest ifconfig.me/ip).Content.Trim()";
    String powerShellOut = PowerShell.executeSingleCommand(command).getCommandOutput();

    // Connection failed
    if (powerShellOut.contains("InvalidOperation")) {
        powerShellOut = null;
    }
    return powerShellOut;
}

Answer 4

It's not that easy since a machine inside a LAN usually doesn't care about the external IP of its router to the internet.. it simply doesn't need it!

I would suggest you to exploit this by opening a site like http://www.whatismyip.com/ and getting the IP number by parsing the html results.. it shouldn't be that hard!

Answer 5

http://jstun.javawi.de/ will do it - provided your gateway device does STUN )most do)

Answer 6

System.out.println(pageCrawling.getHtmlFromURL("http://ipecho.net/plain"));