Get default gateway in java

Question

I want to fetch default gateway for local machine using java. I know how to get it by executing dos or shell commands, but is there any another way to fetch? Also need to fetch primary and secondary dns ip.

Answer 1

My way is:

try(DatagramSocket s=new DatagramSocket())
{
    s.connect(InetAddress.getByAddress(new byte[]{1,1,1,1}), 0);
    return NetworkInterface.getByInetAddress(s.getLocalAddress()).getHardwareAddress();
}

Because of using datagram (UDP), it isn't connecting anywhere, so port number may be meaningless and remote address (1.1.1.1) needn't be reachable, just routable.

Answer 2

In Windows with the help of ipconfig:

import java.awt.Desktop;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URI;

public final class Router {

    private static final String DEFAULT_GATEWAY = "Default Gateway";

    private Router() {
    }

    public static void main(String[] args) {
        if (Desktop.isDesktopSupported()) {
            try {
                Process process = Runtime.getRuntime().exec("ipconfig");

                try (BufferedReader bufferedReader = new BufferedReader(
                        new InputStreamReader(process.getInputStream()))) {

                    String line;
                    while ((line = bufferedReader.readLine()) != null) {
                        if (line.trim().startsWith(DEFAULT_GATEWAY)) {
                            String ipAddress = line.substring(line.indexOf(":") + 1).trim(),
                                    routerURL = String.format("http://%s", ipAddress);

                            // opening router setup in browser
                            Desktop.getDesktop().browse(new URI(routerURL));
                        }

                        System.out.println(line);
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

Here I'm getting the default gateway IP address of my router, and opening it in a browser to see my router's setup page.