Hướng dẫn lập trình Client - Server UDP bằng JAVA

- Bước 1: Tạo một tiến trình Server class DatagramServer

import java.net.*;
import java.io.*;
public class DatagramServer {
    public static void main(String[] args) {
        DatagramPacket datapacket, returnpacket;
        int port = 2018;
        int len = 1024;
        try {
            DatagramSocket datasocket = new DatagramSocket(port);
            byte[] buf = new byte[len];
            datapacket = new DatagramPacket(buf, buf.length);
            while (true) {
                try {
                    datasocket.receive(datapacket);
                    returnpacket = new DatagramPacket(
                            datapacket.getData(),
                            datapacket.getLength(),
                            datapacket.getAddress(),
                            datapacket.getPort());

                    datasocket.send(returnpacket);
                } catch (IOException e) {
                    System.err.println(e);
                }
            }
        } catch (SocketException se) {
            System.err.println(se);
        }
    }
}

- Bước 2: Tạo một tiến trình Client class DatagramClient

package server_client_UDP;

import java.net.*;
import java.io.*;
public class DatagramClient {
    public static void main(String[] args) {
        String hostname;
        int port = 2018;
        int len = 1024;
        DatagramPacket sPacket, rPacket;
        if (args.length > 0)
            hostname = args[0];
        else
            hostname = "localhost";
        try {
            InetAddress ia = InetAddress.getByName(hostname);
            DatagramSocket datasocket = new DatagramSocket();
            BufferedReader stdinp = new BufferedReader(new InputStreamReader(System.in));
            while (true) {
                try {
                    String echoline = stdinp.readLine();
                    if (echoline.equals("done")) break;
                    byte[] buffer = new byte[echoline.length()];
                    buffer = echoline.getBytes();
                    sPacket = new DatagramPacket(buffer, buffer.length, ia, port);
                    datasocket.send(sPacket);
                    byte[] rbuffer = new byte[len];
                    rPacket = new DatagramPacket(rbuffer, rbuffer.length);
                    datasocket.receive(rPacket);
                    String retstring = new String(rPacket.getData());
                    System.out.println("Server gửi về: "+retstring);
                } catch (IOException e) {
                    System.err.println(e);
                }
            } // while
        } catch (UnknownHostException e) {
            System.err.println(e);
        } catch (SocketException se) {
            System.err.println(se);
        }
    }  // end main

    public static class DatagramServer {
        public static void main(String[] args) {
            DatagramPacket datapacket, returnpacket;
            int port = 2018;
            int len = 1024;
            try {
                DatagramSocket datasocket = new DatagramSocket(port);
                byte[] buf = new byte[len];
                datapacket = new DatagramPacket(buf, buf.length);
                while (true) {
                    try {
                        datasocket.receive(datapacket);
                        returnpacket = new DatagramPacket(
                                datapacket.getData(),
                                datapacket.getLength(),
                                datapacket.getAddress(),
                                datapacket.getPort());
                        datasocket.send(returnpacket);
                    } catch (IOException e) {
                        System.err.println(e);
                    }
                }
            } catch (SocketException se) {
                System.err.println(se);
            }
        }
    }
}

Chạy cả 2 chương trình cùng lúc, và gõ một chuỗi bên phía client , client ---> server và server ---> client để hiện ra màn hình.