Network programming

1, Overview

Network programming refers to writing programs that run on multiple devices (computers), which are connected through the network

1.1 two elements of network communication:

1. Address of both parties:

• ip

• Port number

1. Rules: protocols for network communication

• TCP/IP

  Reference model:
  

1.2 IP

ip address: inetAddress

• Uniquely locate a computer on the network

• 127.0.0.1 == localhost (native)

• Classification of ip addresses

  • IPv4: 127.0.0.1 4 bytes, 0-255 4.2 billion

  • IPv6: 128 bits, 8 unsigned integers

• Public network (Internet) / private network (LAN)

• Domain name: www.jd.com

(InetAddress) Click to view the code

InetAddress inetAddress1 = InetAddress.getByName("127.0.0.1");
InetAddress inetAddress2 = InetAddress.getByName("localhost");
InetAddress inetAddress3 = InetAddress.getLocalHost();
InetAddress inetAddress4 = InetAddress.getByName("www.baidu.com");

1.3 port

The port represents the process of a program on the computer:

• Different processes have different port numbers to distinguish software

• Range: 0 - 65535

• TCP/UDP : 65535*2 tcp:80 udp:80 ; Port numbers cannot conflict under the same protocol

• Port classification:

  • Common ports: 0 ~ 1023

    • HTTP: 80

    • HTTPS: 443

    • FTP: 21

    • Telnet: 23

  • Program registration port: 1024 ~ 49151, assign users or register programs

    • Tomcat: 8080

    • MySQL: 3306

    • Oracle: 1521

  • Dynamic and private: 49152 ~ 65535

(InetSocketAddress) Click to view the code

public static void main(String[] args) throws UnknownHostException {
        InetSocketAddress address1 = new InetSocketAddress("127.0.0.1", 8080);
        InetSocketAddress address2 = new InetSocketAddress("localhost", 8080);
        InetSocketAddress address3 = new InetSocketAddress(InetAddress.getByName("127.0.0.1"), 8080);
        System.out.println(address1);  // /127.0.0.1:8080
        System.out.println(address2);  // localhost/127.0.0.1:8080
        System.out.println(address3);  // /127.0.0.1:8080
        System.out.println("--------------------------------");
        System.out.println(address1.getPort());  // 8080
        System.out.println(address1.getAddress());  // /127.0.0.1
        System.out.println(address1.getHostName());  // 127.0.0.1
        System.out.println(address1.getHostString()); // 127.0.0.1
        System.out.println(address1.getClass());  // 
    }

1.4 communication protocol

Agreement: agreement

TCP/IP protocol cluster: it is actually a group of protocols

• TCP: Transmission Control Protocol

• UDP: User Datagram Protocol

• IP: network interconnection protocol

TCP/UDP comparison:

• TCP: call

  • Connection, stable

  • Three handshakes and four waves

  • Client, server

  • The transmission is completed, the connection is released, and the efficiency is low

• UDP: send SMS

  • No connection, unstable

  • Client, server, no clear boundary (sender, receiver)

  • Ready or not, it can be sent

  • High efficiency, but packet loss may occur

  • Lack of reliability may result in loss, errors, and duplicate packets

  • DDOS: flood attack! (saturation attack)

1.5 TCP

TCP:(Transmission Control Protocol)

client:

1. Connect to the server Socket

2. send message

Server:

1. Establish the service port: ServerSocket

2. Waiting for the user's connection (listening): accept()

3. Receive messages from users

Client code:

Click to view the code

package cn.com.longer.test.netWorkProgram.tcp;

import java.io.IOException;
import java.io.OutputStream;
import java.net.InetAddress;
import java.net.Socket;

/**
 * TCP client
 */
public class TcpClientDemo01 {
    public static void main(String[] args) {
        Socket socket = null;
        OutputStream os = null;
        try {
            // 1. Know the address of the server: IP port number
            InetAddress serverIp = InetAddress.getByName("127.0.0.1");
            int port = 9999;
            // 2. Create a socket connection
            socket = new Socket(serverIp,port);
            // 3. Send message IO stream
            os = socket.getOutputStream();
            os.write("You ha ah, use Watson ewefef Three Dongfeng four".getBytes());
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            if (socket != null){
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (os != null){
                try {
                    os.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

Server code:

Click to view the code

package cn.com.longer.test.netWorkProgram.tcp;


import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;

/**
 * TCP Server
 */
public class TcpServerDemo01 {
    public static void main(String[] args) {
        ServerSocket serverSocket = null;
        Socket socket =null;
        InputStream is =null;
        ByteArrayOutputStream baos = null;
        try {
            // 1. Server: I want to have an address
            serverSocket = new ServerSocket(9999);
            // 2. Wait for the client to connect and listen
            socket = serverSocket.accept();
            // 3. Read the message from the client
            is = socket.getInputStream();
            // Pipe flow
            baos = new ByteArrayOutputStream();
            byte[] buffer = new byte[1024];
            int len;
            while ((len = is.read(buffer)) != -1){
                baos.write(buffer, 0, len);
            }
            System.out.println(baos.toString());

            /*
                byte[] bytes = new byte[1024];
                int len;
                while ((len=is.read(buffer)) != -1){
                    String msg = new String(buffer, 0, len);
                    System.out.println(msg);
                }
            */
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            // Closed flow
            if (baos != null){
                try {
                    baos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (is != null){
                try {
                is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (socket != null){
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (serverSocket != null){
                try {
                    serverSocket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

1.6 UDP

UDP: (User Datagram Protocol), user datagram protocol

Texting: don't connect, but you need to know each other's address!

Sender (code):

Click to view the code

package cn.com.longer.test.netWorkProgram.udp;

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

/**
 * UDP Sender
 */
public class UdpClientDemo01 {
    public static void main(String[] args) throws Exception {
        // 1. Create a socket
        DatagramSocket socket = new DatagramSocket();
        // 2. Component package
        String msg = "UDP Hello!!!";
        InetAddress ip = InetAddress.getByName("127.0.0.1");
        int port = 9090;

        // Who is the starting length of the packet to send
        DatagramPacket datagramPacket = new DatagramPacket(msg.getBytes(), 0, msg.getBytes().length, ip, port);
        // 3. Send packet
        socket.send(datagramPacket);
        // 4. Close the flow
        socket.close();
    }
}

Receiver (code):

Click to view the code

package cn.com.longer.test.netWorkProgram.udp;

import java.net.DatagramPacket;
import java.net.DatagramSocket;

/**
 * UDP Receiver
 */
public class UdpServerDemo01 {
    public static void main(String[] args) throws Exception {
        // 1. Create socket and open port
        DatagramSocket socket = new DatagramSocket(9090);
        // 2. Receive packets
        byte[] buffer = new byte[1024];
        DatagramPacket datagramPacket = new DatagramPacket(buffer, 0, buffer.length);

        socket.receive(datagramPacket); // Blocking reception

        System.out.println(datagramPacket.getAddress().getHostName());
        System.out.println(datagramPacket.getData().toString());
        System.out.println(new String(datagramPacket.getData(), 0, datagramPacket.getLength()));

        // 3. Close the flow
        socket.close();
    }
}

1.7 URL

Uniform resource locator: to locate resources, locate a resource on the Internet!

DNS domain name resolution (resolve a domain name to IP): www.baidu.com com ---> https://220.181.38.149/
Protocol: / / IP address: port number / project name / resource

URLDemo:

Click to view the code

public static void main(String[] args) throws Exception {
        URL url = new URL("https://space.bilibili.com/29038862/fans/follow?spm_id_from=333.1007.0.0");
        System.out.println(url.getProtocol());
        System.out.println(url.getHost());
        System.out.println(url.getPort());
        System.out.println(url.getPath());
        System.out.println(url.getFile());
        System.out.println(url.getQuery());
    }

URLDown:

Click to view the code

package cn.com.longer.test.netWorkProgram;

import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class UrlDown {
    public static void main(String[] args) throws Exception {
        // 1. Download address
        URL url = new URL("https://webfs.tx.kugou.com/202201071810/4d1be68a4efcbd709473a9d7d8f1013c/part/0/960141/G229/M0A/1A/07/xZQEAF9Iv6SAHH0xAEiEHQZqX8E377.mp3");
        // 2. Connect to this resource HTTP
        HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
//        HttpsURLConnection urlConnection = (HttpsURLConnection) url.openConnection();
        InputStream is = urlConnection.getInputStream();
        FileOutputStream fos = new FileOutputStream("loveOneLife.m4a");

        byte[] buffer = new byte[1024];
        int len;
        while ((len=is.read(buffer)) != -1){
            // Write this data
            fos.write(buffer, 0, len);
        }
        fos.close();
        is.close();
        urlConnection.disconnect();
    }
}