How to implement UDP programming for network communication based on UDP protocol in Java

UDP programming communication

Basic introduction

• The classes DatagramSocket and DatagramPacket [data packet/datagram] implement network programs based on the UDP protocol.

• UDP datagrams are sent and received through the datagram socket DatagramSocket. The system does not guarantee that the UDP datagram will be safely delivered to the destination, nor is it sure when it will arrive.

• The DatagramPacket object encapsulates a UDP datagram. The datagram contains the IP address and port number of the sender and the IP address and port number of the receiver.

• Each datagram in the UDP protocol gives complete address information, so there is no need to establish a connection between the sender and the receiver.

Basic process

• The two core classes/objects DatagramSocket domain DatagramPacket

• Establish and send end, receiving end.

• Create a data packet

• Call the send and receive methods of DatagramSocket

• Close DatagramSocket.

Schematic diagram of UDP network programming principle

UDP description:

• No clear The server and client evolved into the sender and receiver of data.

• Receiving data and generating data are completed through the DatagramSocket object.

• Encapsulate data into DatagramPacket object/package.

• When receiving the DatagramPacket object, it needs to be unpacked and the data taken out.

• DatagramSocket can specify the port on which to receive the data.

package com.study.srv.demo18;
import java.io.IOException;
import java.net.*;
/**
 * @version 1.0
 * UDP发送端
 */
public class Demo11 {
    public static void main(String[] args) throws IOException {
        //1.创建DatagramSocket对象，准备发送和接收数据,在9998端口接收
        DatagramSocket datagramSocket = new DatagramSocket(9998);
        //2.将需要发送的数据，封装到DatagramPacket对象
        String s="发送的数据";
        byte[] buf=s.getBytes();
        InetAddress ip = InetAddress.getByName("192.168.0.18");
        //说明：封装的DatagramPacket对象
        //buf 内容字节数组
        //buf.length 数据长度
        //ip 主机（ip）
        //9999 端口
        DatagramPacket packet = new DatagramPacket(buf, buf.length, ip, 9999);
        //发送数据
        datagramSocket.send(packet);
        //关闭资源
//        datagramSocket.close();
        System.out.println("发送完毕");
        //发送端变为接收端接收数据
        byte[] bytes = new byte[1024];
        DatagramPacket datagramPacket = new DatagramPacket(bytes, bytes.length);
        datagramSocket.receive(datagramPacket);
        int length = datagramPacket.getLength();
        byte[] data = datagramPacket.getData();
        String string = new String(data, 0, length);
        System.out.println(string);
        datagramSocket.close();
        System.out.println("接受结束");
    }
}

package com.study.srv.demo18;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
/**
 * @version 1.0
 *UDP接收端
 */
public class Demo10 {
    public static void main(String[] args) throws IOException {
        //1．创建一个 DatagramSocket对象，准备在9999接收数据
        DatagramSocket datagramSocket = new DatagramSocket(9999);
        //2．构建一个DatagramPacket 对象，准备接收数据
        //在UDP协议，一个数据包最大64k
        byte[] buf=new byte[1024];
        DatagramPacket packet = new DatagramPacket(buf, buf.length);
        //3.接收方法 将通过网络传输的DatagramPacket对象填充到packet里去。
        System.out.println("接收端等待接收");
        datagramSocket.receive(packet);
        //4.可以对packet进行拆包，取出数据，并显示
        //实际接收到的数据字节长度
        int length = packet.getLength();
        //实际接收到的数据
        byte[] data = packet.getData();
        String string = new String(data, 0, length);
        System.out.println(string);
        //5.关闭资源
//        datagramSocket.close();
        System.out.println("接收结束");
        //接收端变为发送端，发送数据
        String s="接收端变为发送端，发送数据";
        byte[] bytes=s.getBytes();
        DatagramPacket datagramPacket = new DatagramPacket(bytes, bytes.length, InetAddress.getByName("192.168.0.18"), 9998);
        datagramSocket.send(datagramPacket);
        datagramSocket.close();
        System.out.println("发送完毕");
    }
}

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