import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.util.Base64;

public class Server {
	public static void main(String[] args) throws Exception {
		//建立UDP伺服器物件
		DatagramSocket ds = new DatagramSocket(5555);
		//建立資料包
		byte[] bs = new byte[64];
		DatagramPacket dp = new DatagramPacket(bs, bs.length);
		
		//使用伺服器物件接收資料 放進資料包中
		ds.receive(dp);
		byte[] bs2 = dp.getData();//64
		byte[] bs3 = Base64.getDecoder().decode(bs2);
		System.out.println(new String(bs3));
		
	}
}
 

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.Inet4Address;
import java.util.Base64;

public class Client {
	public static void main(String[] args) throws Exception {
		//建立客戶端物件
		DatagramSocket socket = new DatagramSocket();
		//建立資料包
		byte[] bs = "{type:001,content:你好嗎?}".getBytes();
		byte[] bs2 = new byte[64];
		//拷貝資料
		for (int i = 0; i < bs.length; i++) {
			bs2[i] = bs[i];
		}
		//空的地方填充0
		for (int i = bs.length; i < 64; i++) {
			bs2[i] = 0;
		}
		//加密
		String string = Base64.getEncoder().encodeToString(bs2);
		DatagramPacket dp = new DatagramPacket(string.getBytes(), 64,Inet4Address.getLocalHost(),5555);
		//傳送資料包
		socket.send(dp);
	}
}