Question

How can I determine the IP of my router/gateway in Java? I can get my IP easily enough. I can get my internet IP using a service on a website. But how can I determine my gateway’s IP?

This is somewhat easy in .NET if you know your way around. But how do you do it in Java?

Answer 1

Java doesn’t make this as pleasant as other languages, unfortunately. Here’s what I did:

import java.io.*; import java.util.*;  public class ExecTest {     public static void main(String[] args) throws IOException {         Process result = Runtime.getRuntime().exec('traceroute -m 1 www.amazon.com');          BufferedReader output = new BufferedReader(new InputStreamReader(result.getInputStream()));         String thisLine = output.readLine();         StringTokenizer st = new StringTokenizer(thisLine);         st.nextToken();         String gateway = st.nextToken();         System.out.printf('The gateway is %s\n', gateway);     } } 

This presumes that the gateway is the second token and not the third. If it is, you need to add an extra st.nextToken(); to advance the tokenizer one more spot.