User

package com.imooc.UTPReturn;

import java.io.Serializable;

public class User implements Serializable{
  
  private String username;
  
  private String password;

  public User(String username, String password) {
    
    this.username = username;
    this.password = password;
  }

  @Override
  public String toString() {
    return "User [username=" + username + ", password=" + password + "]";
  }

  public String getUsername() {
    return username;
  }

  public void setUsername(String username) {
    this.username = username;
  }

  public String getPassword() {
    return password;
  }

  public void setPassword(String password) {
    this.password = password;
  }
  
  

}

Server

package com.imooc.UTPReturn;

import java.io.ByteArrayInputStream;
import java.io.ObjectInputStream;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

public class UTPServer {

  public static void main(String[] args) throws Exception {

    /*
     * 服务器端接收客户端的请求
     */
    // 创建服务器端DatagramSocket
    DatagramSocket socket = new DatagramSocket(8800);

    // 创建数据包
    byte[] data = new byte[1024];
    DatagramPacket packet = new DatagramPacket(data, data.length);

    // 服务器端已经启动...
    System.out.println("服务器端已经 启动....");
    socket.receive(packet);// 接收数据

    // 读取客户端发来的数据
    // String str=new String(data, 0, packet.getLength());
    // System.out.println("我是服务器，客户端说："+str);

    // bytearray to object
    ByteArrayInputStream bi = new ByteArrayInputStream(data);
    ObjectInputStream oi = new ObjectInputStream(bi);

    User user = (User)oi.readObject();
    bi.close();
    oi.close();
    System.out.println(user.toString());
    
    

    /*
     * 服务器端回应客户端
     */
    // 给客户端发出响应
    byte[] responseData = null;
    responseData = "欢迎你".getBytes();
    InetAddress address = packet.getAddress();
    int port = packet.getPort();

    DatagramPacket responsePacket = new DatagramPacket(responseData,
        responseData.length, address, port);

    socket.send(responsePacket);

    // 关闭资源
    socket.close();
  }

}

Client

package com.imooc.UTPReturn;

import java.io.ByteArrayOutputStream;
import java.io.ObjectOutputStream;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

public class UTPClient {

  public static void main(String[] args) throws Exception {
    /*
     * 客户端向服务器端发送数据
     */
    // 定义数据报的地址，端口，数据
    InetAddress address = InetAddress.getByName("localhost");
    int port = 8800;
    // 定义数据报的内容
    // byte[] data="用户名admin,密码123".getBytes();
    User user = new User("张三", "123");
    byte[] data = null;
    
    
    // object to bytearray
    ByteArrayOutputStream bo = new ByteArrayOutputStream();
    ObjectOutputStream oo = new ObjectOutputStream(bo);
    oo.writeObject(user);
    data = bo.toByteArray();

    bo.close();
    oo.close();
    // 创建数据报
    DatagramPacket packet = new DatagramPacket(data, data.length, address,
        port);

    // 创建DatagramSocket对象
    DatagramSocket socket = new DatagramSocket();

    // 发送数据报
    socket.send(packet);

    /*
     * 客户端接收服务器端的回应
     */
    socket.receive(packet);

    String responseStr = new String(data, 0, packet.getLength());
    System.out.println("我是客户端，服务器端回应说：" + responseStr);

  }

}