客户端

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;

public class LoginClient {
    public static void main(String[] args) {
        String info = "你好，我想咨询一个问题";
        byte[] infos = info.getBytes();
        //IP地址获取方法
        InetAddress ia;
        DatagramSocket socket =null;
        try {
            ia = InetAddress.getByName("localhost");
            DatagramPacket dp = new DatagramPacket(infos, infos.length, ia, 5000);
            socket = new DatagramSocket();
            socket.send(dp);
             
            //接收服务端信息
            byte[] replys = new byte[1024];
            DatagramPacket dp1 = new DatagramPacket(replys,replys.length);
            socket.receive(dp1);
            String reply = new String(dp1.getData(),0,dp1.getData().length);
            System.out.println("服务器说："+reply);
             
             
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (SocketException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally{
            socket.close();
        }
         
         
         
    }
}

服务器端

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketAddress;
import java.net.SocketException;


public class LoginService {
    public static void main(String[] args) {
        DatagramSocket socket = null;
        byte[] info = new byte[1024];
        DatagramPacket dp = new DatagramPacket(info, info.length);
        try {
            socket = new DatagramSocket(5000);
            socket.receive(dp);
            
            String infos = new String(dp.getData(), 0, dp.getData().length);
            System.out.println("客户端说："+infos);
            
            //给客户端一个响应
            String reply = "你好，有什么问题请说";
            SocketAddress sa = dp.getSocketAddress();
            DatagramPacket dp1 = new DatagramPacket(reply.getBytes(), 0, reply.getBytes().length, sa);
            socket.send(dp1);
            
            
        } catch (SocketException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally{
            socket.close();
        }
        
    }
}