什么是网络编程？Java如何实现？三次握手和四次挥手？

/**
 * @author .29.
 * @create 2023-10-20 16:44
 */
public class UDPSendM {
    public static void main(String[] args) throws IOException {
        //1. 创建DatagramSocket对象
        // 绑定端口：通过绑定的端口向外发送数据
        //空参:随机选取所有可用端口中的一个来绑定
        //带参：指定端口号进行绑定
        DatagramSocket datagramSocket = new DatagramSocket();
        //2. 打包数据
        String str = "这是使用UDP协议发送的数据";//数据
        byte[] bytes = str.getBytes();        //转换成字节数组
        InetAddress address = InetAddress.getByName("127.0.0.1"); //向这个主机地址发送数据
        int port = 10086; //向这个端口发送数据
        DatagramPacket datagramPacket = new DatagramPacket(bytes, bytes.length, address, port);
        //3. 发送数据
        datagramSocket.send(datagramPacket);
        //4.关闭资源
        datagramSocket.close();
    }
}

/**
 * @author .29.
 * @create 2023-10-20 17:10
 */
public class UDPReceiveM {
    public static void main(String[] args) throws IOException {
        //1. 创建DatagramSocket对象，必须绑定端口号，并与发送程序的目标端口一致
        DatagramSocket datagramSocket = new DatagramSocket(10086);
        //2. 接收数据
        byte[] bytes = new byte[1024];
        DatagramPacket datagramPacket = new DatagramPacket(bytes, bytes.length);
        //receive()是阻塞的，在接收到数据前会一直等待
        datagramSocket.receive(datagramPacket);
        //3. 解析数据
        byte[] data = datagramPacket.getData(); //传输的数据
        InetAddress address = datagramPacket.getAddress();//传输的地址
        int length = datagramPacket.getLength();//数据长度
        int port = datagramPacket.getPort();//传输的端口号
        System.out.println("接收到的数据：" + new String(data,0,length));
        System.out.println("数据从端口" + port + "地址" + address + "发来");
        //4. 释放资源
        datagramSocket.close();
    }
}

接收到的数据：这是使用UDP协议发送的数据
数据从端口50584地址/127.0.0.1发来

MulticastSocket ms = new MulticastSocket();

MulticastSocket ms = new MulticastSocket(10000);
//获取组播地址的对象
InetAddress address = InetAddress.getByName("224.0.0.1");
//MulticastSocket对象添加绑定到组播地址
ms.joinGroup(address);

/**
 * @author .29.
 * @create 2023-10-20 20:14
 */
public class TCPClient {
    public static void main(String[] args) throws IOException {
        //1. 创建Socket对象，与服务端建立连接
        Socket socket = new Socket("127.0.0.1", 10000);
        //2. 获取字节输出流
        OutputStream outputStream = socket.getOutputStream();
        //3. 发送数据
        String s = "这边是客户端，你好呀服务端！";
        outputStream.write(s.getBytes());
        //4. 关闭资源
        outputStream.close();
        socket.close();
    }
}

/**
 * @author .29.
 * @create 2023-10-20 20:17
 */
public class TCPServer {
    public static void main(String[] args) throws IOException {
        //1. 获取服务端Socket对象，端口号与客户端目标端口号一致
        ServerSocket serverSocket = new ServerSocket(10000);
        //2. 返回一个Socket对象
        Socket accept = serverSocket.accept();
        //3. 获取字节输入流
        InputStream inputStream = accept.getInputStream();
        InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
        //4. 获取数据，显示
        int i;
        System.out.println("接收到数据：");
        while((i = inputStreamReader.read()) != -1){
            System.out.print((char)i);
        }
        //5. 释放资源
        inputStreamReader.close();
        accept.close();
        serverSocket.close();
    }
}

/**
 * @author .29.
 * @create 2023-10-20 15:51
 */
public class InetAddressDemo {
    public static void main(String[] args) throws UnknownHostException {
        //1. 获取InetAddress对象（一台设备的对象），传入的可以是IP地址，也可以是机器名称
        InetAddress inetAddress = InetAddress.getByName("LAPTOP-TB1IVJR9");
        System.out.println(inetAddress); // LAPTOP-TB1IVJR9/192.168.88.1
        InetAddress inetAddress2 = InetAddress.getByName("192.168.88.1");
        System.out.println(inetAddress2); // /192.168.88.1
        //2. 获取InetAddress对象的设备名称
        String hostName = inetAddress.getHostName();
        System.out.println(hostName); // LAPTOP-TB1IVJR9
        //3. 获取InetAddress对象的ip地址字符串
        String hostAddress = inetAddress.getHostAddress();
        System.out.println(hostAddress); // 192.168.88.1
    }
}