DNSServer.java

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.util.HashMap;

public class DNSServer {

    private static String normalizeDomain(String input) {
        String domain = input.trim().toLowerCase();

        if (domain.startsWith("http://")) {
            domain = domain.substring(7);
        } else if (domain.startsWith("https://")) {
            domain = domain.substring(8);
        }

        int slashIndex = domain.indexOf('/');
        if (slashIndex != -1) {
            domain = domain.substring(0, slashIndex);
        }

        return domain;
    }

    public static void main(String[] args) {
        try {
            DatagramSocket socket = new DatagramSocket(9876);
            System.out.println("DNS Server started...");

            HashMap<String, String> dnsTable = new HashMap<>();
            dnsTable.put("www.google.com", "142.250.190.78");
            dnsTable.put("google.com", "142.250.190.78");
            dnsTable.put("www.yahoo.com", "98.137.11.163");
            dnsTable.put("yahoo.com", "98.137.11.163");
            dnsTable.put("www.example.com", "93.184.216.34");
            dnsTable.put("example.com", "93.184.216.34");

            byte[] receiveData = new byte[1024];

            while (true) {
                DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
                socket.receive(receivePacket);

                String rawInput = new String(receivePacket.getData(), 0, receivePacket.getLength());
                String domainName = normalizeDomain(rawInput);

                System.out.println("Query received: " + rawInput + " -> " + domainName);
                String ipAddress = dnsTable.getOrDefault(domainName, "Domain not found");

                byte[] sendData = ipAddress.getBytes();
                InetAddress clientAddress = receivePacket.getAddress();
                int clientPort = receivePacket.getPort();

                DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, clientAddress, clientPort);
                socket.send(sendPacket);
            }

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