Java Network Programming

Computer network

Computer network refers to a computer system that connects a number of independent computers and their external devices with different geographical locations through communication lines. Under the management and coordination of network operating system, network management software and network communication protocol, resources sharing and information transfer can be realized.

The purpose of network programming

• Radio station
• Spread and exchange information
• Data interchange
• communication
• .

Elements of network communication

How to realize network communication?

1. Address of the communication party

   • IP – Locates a particular computer
   • Port number – Locate to an application
   • 47.99.72.134:1025

2. Communication protocol

3. This section focuses on TCP and UDP at the transport layer

IP

IP address: InetAddress

• Uniquely locate a computer on a network
• 127.0.0.1: Local (localhost)
• IP Address Classification
  • ipv4 / ipv6
    • Ipv4:47.99.72.134, 4 bytes, total 4.2 billion; End of 2019
    • Ipv6: CDCD: 910 a: 2222-5498:8475-1111:3900-2020128, each with 16 * *, * * is separated, every four expressed in a hexadecimal number, 2 ^ 128 (about 3.4 * 10 ^ 38)
  • Public network/Private Network (LAN)
    • The ABCD class address
    • 192.168. XXX. XXX private network
  • Domain name: IP address cannot be remembered

java.net.InetAddress

package com.volcano.net;

import java.net.InetAddress;
import java.net.UnknownHostException;

public class TestInetAddress {
    public static void main(String[] args) {
        try {
            InetAddress address = InetAddress.getByName("www.baidu.com");
            System.out.println(address);/ / www.baidu.com/180.101.49.11
            InetAddress address2 = InetAddress.getByName("127.0.0.1");
            System.out.println(address2);/ / / 127.0.0.1
            InetAddress address3 = InetAddress.getLocalHost();
            System.out.println(address3);/ / DESKTOP - 9 poar2h / 10.238.60.12
        } catch(UnknownHostException e) { e.printStackTrace(); }}}Copy the code

port

A port represents the process of a program on a computer.

• Different processes have different port numbers

• Regulations, 0 ~ 65535

• TCP and UDP have 6W + each

• Port classification

  • Public ports 0 to 1023 are mostly used by built-in applications

    • 80 HTTP:
    • HTTPS: 443
    • FTP: 21
    • Telnet: 23

  • Program registration port: 1024~49151 for assigning users or programs

    • The Oracle: 1521
    • Mysql: 3306
    • Tomcat: 8080

  • Dynamic allocation or private: 49152 to 65535

    Netstat ano# view all ports netstat ano | findstr searches "80" # view all specified port tasklist: findstr searches "80" # check the progress of the specified portCopy the code

java.net.InetSocketAddress

package com.volcano.net;

import java.net.InetSocketAddress;

public class TestInetSocketAddress {
    public static void main(String[] args) {
        InetSocketAddress inetSocketAddress = new InetSocketAddress("127.0.0.1".8080);
        System.out.println(inetSocketAddress);
        InetSocketAddress inetSocketAddress2 = new InetSocketAddress("localhost".8080); System.out.println(inetSocketAddress2); System.out.println(inetSocketAddress.getAddress()); System.out.println(inetSocketAddress.getHostName()); System.out.println(inetSocketAddress.getPort()); }}Copy the code

Communication protocol

Network communication protocol: rate, bit rate, code structure, transmission control…

TCP/IP protocol cluster: Actually a group of protocols

Important:

• TCP: user transport protocol
• UDP: user datagram protocol

Famous agreement

• TCP
• IP

Comparison between TCP and UDP

TCP: Make a call

• Connection, stabilization

• Three handshakes, four waves

  At least three times to ensure A stable connection A: What do you see? B: What do you think? A: Give it A go! Disconnect at least 4 times A: I'm leaving B: Are you really leaving? B: Are you really, really leaving? A: I really have to goCopy the code

• Client, server

UDP: Sends SMS messages

• Not connected or stable
• Client, server: No clear boundaries
• Ready or not, I can send it to you
• DDOS: Flood attacks, sending spam messages, occupying target ports, and jamming the network

TCP

Implement chatting

package com.volcano.net;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;
// Run this class first
public class TcpServerDemo1 {
    public static void main(String[] args) {
        // All need to be closed, so all need to be extracted first
        ServerSocket serverSocket=null;
        Socket socket=null;
        InputStream socketInputStream=null;
        ByteArrayOutputStream byteArrayOutputStream=null;
        try {
            //1. You must have an address first
            serverSocket = new ServerSocket(9999);
            // Loop to receive messages
            while(true) {//2. Wait for the client to connect
                socket = serverSocket.accept();
                //3. Read client messages
                socketInputStream = socket.getInputStream();
                // Pipe flow is appropriate
                byteArrayOutputStream = new ByteArrayOutputStream();
                byte[] buffer=new byte[1024];
                int len;
                while((len=socketInputStream.read(buffer))! = -1){
                    byteArrayOutputStream.write(buffer,0,len); } System.out.println(byteArrayOutputStream.toString()); }}catch (IOException e) {
            e.printStackTrace();
        }finally {
            // It is necessary to close all of them by using if to judge and then close them
            if(byteArrayOutputStream! =null) {try {
                    byteArrayOutputStream.close();
                } catch(IOException e) { e.printStackTrace(); }}if(socketInputStream! =null) {try {
                    socketInputStream.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();
                }
            }
        }
    }
}
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package com.volcano.net;

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

public class TcpClientDemo1 {
    public static void main(String[] args) {
        Socket socket=null;
        OutputStream outputStream=null;
        try {
            //1. Obtain the server address
            InetAddress address = InetAddress.getByName("127.0.0.1");
            / / the port number
            int port = 9999;
            2. Create a Socket connection
            socket = new Socket(address, 9999);
            //3. Send message I/O flow
            outputStream = socket.getOutputStream();
            outputStream.write("aaaa".getBytes());
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            if(outputStream! =null) {try {
                    outputStream.close();
                } catch(IOException e) { e.printStackTrace(); }}if(socket! =null) {try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}
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Transfer files

package com.volcano.net;

import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;

public class TcpServerDemo02 {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(9999);
        Socket socket = serverSocket.accept();
        InputStream socketInputStream = socket.getInputStream();
        FileOutputStream fileOutputStream = new FileOutputStream(new File("222.jpg"));
        byte[] buffer = new byte[1024];
        int len;
        while((len=socketInputStream.read(buffer))! = -1){
            fileOutputStream.write(buffer,0, len);
        }
        // After receiving the message, tell the client
        OutputStream socketOutputStream = socket.getOutputStream();
        socketOutputStream.write("I'm ready, you disconnect.".getBytes()); fileOutputStream.close(); socketInputStream.close(); serverSocket.close(); }}Copy the code

package com.volcano.net;

import java.io.*;
import java.net.InetAddress;
import java.net.Socket;

public class TcpClientDemo02 {
    public static void main(String[] args) throws Exception {
        Socket socket = new Socket(InetAddress.getByName("127.0.0.1"), 9999);
        OutputStream outputStream = socket.getOutputStream();
        // Create a file input stream
        FileInputStream fileInputStream = new FileInputStream(new File("Tutor wallpaper.jpg"));
        byte[] buffer = new byte[1024];
        int len;
        // The file is written to the socket output stream
        while((len=fileInputStream.read(buffer))! = -1){
            outputStream.write(buffer,0,len);
        }
        // When the transmission is complete, tell the server
        socket.shutdownOutput();
        // Result of receiving server message
        InputStream socketInputStream = socket.getInputStream();
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        int len2;
        byte[] buffer2 = new byte[1024];
        while((len2=socketInputStream.read(buffer2))! = -1){
            byteArrayOutputStream.write(buffer2,0,len2); } System.out.println(byteArrayOutputStream.toString()); fileInputStream.close(); outputStream.close(); socket.close(); }}Copy the code

UDP

Message is sent

package com.volcano.net;

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

public class UdpClientDemo {
    public static void main(String[] args) throws Exception {
        //1. Create a Socket
        DatagramSocket socket = new DatagramSocket();
        / / 2. Set up a package
        String msg = "Hello, server.";
        // Send to destination
        InetAddress localhost = InetAddress.getByName("localhost");
        int port=9999;
        DatagramPacket packet = new DatagramPacket(msg.getBytes(), 0, msg.getBytes().length, localhost, port);
        / / 3. Sendsocket.send(packet); socket.close(); }}Copy the code

package com.volcano.net;

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

public class UdpServerDemo {
    public static void main(String[] args) throws Exception {
        // Open the port
        DatagramSocket socket=new DatagramSocket(9999);
        // Receive the packet, still need to wait for the client to connect
        byte[] buffer = new byte[1024];
        DatagramPacket packet = new DatagramPacket(buffer, 0, buffer.length);
        socket.receive(packet);// block reception
        System.out.println(packet.getAddress().getHostAddress());
        System.out.println(new String(packet.getData(),0,packet.getLength())); socket.close(); }}Copy the code

Chat implementation

Multi-threaded chat.

Create send and receive threads

package com.volcano.net.chat;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

public class TalkSend implements Runnable {
    DatagramSocket socket=null;
    BufferedReader reader=null;
    int thisPort;
    String toHost;
    int toPort;

    public TalkSend(int fromPort, String toHost, int toPort) {
        this.thisPort = fromPort;
        this.toHost = toHost;
        this.toPort = toPort;
    }

    @Override
    public void run(a) {
        try {
            socket = new DatagramSocket(thisPort);

            // Prepare data: console read
            reader = new BufferedReader(new InputStreamReader(System.in));
            // Send in a loop
            while (true){
                String data = reader.readLine();
                byte[] datas = data.getBytes();
                DatagramPacket packet = new DatagramPacket(datas,0,datas.length, InetAddress.getByName(toHost),toPort);
                socket.send(packet);
                if(data.equals("bye")) {break; }}}catch(IOException e) { e.printStackTrace(); } socket.close(); }}Copy the code

package com.volcano.net.chat;

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

public class TalkReceive implements Runnable {
    DatagramSocket socket=null;
    int thisPort;
    String  fromWho;

    public TalkReceive(int thisPort, String fromWho) {
        this.thisPort = thisPort;
        this.fromWho = fromWho;
    }

    @Override
    public void run(a) {
        try {
            socket = new DatagramSocket(thisPort);
            // loop to receive
            while (true) {byte[] buffer = new byte[1024];
                DatagramPacket packet = new DatagramPacket(buffer,0,buffer.length);
                socket.receive(packet);
                byte[] data=packet.getData();
                String strData=new String(data,0,data.length);
                System.out.println(fromWho+"："+strData);
                if(strData.trim().equals("bye")) {break;
                }
            }
            socket.close();
        } catch(IOException e) { e.printStackTrace(); }}}Copy the code

Run the thread on the student side and the teacher side, note the port correspondence

package com.volcano.net.chat;

public class Student {
    public static void main(String[] args) {
        new Thread(new TalkSend(6666."localhost".9999)).start();
        new Thread(new TalkReceive(8888."Teacher")).start(); }}Copy the code

package com.volcano.net.chat;

public class Teacher {
    public static void main(String[] args) {
        new Thread(new TalkSend(7777."localhost".8888)).start();
        new Thread(new TalkReceive(9999."Student")).start(); }}Copy the code

URL

Uniform resource locator

package com.volcano.net;

import java.net.MalformedURLException;
import java.net.URL;

public class TestURL {
    public static void main(String[] args) throws MalformedURLException {
        URL url=new URL("http://localhost:8080/helloworld/index.jsp? username=kuangshen&password=123");
        System.out.println(url.getProtocol());/ / agreement
        System.out.println(url.getHost());/ / host IP
        System.out.println(url.getPort());/ / port
        System.out.println(url.getPath());/ / file
        System.out.println(url.getFile());/ / the full path
        System.out.println(url.getQuery());/ / parameters}}Copy the code

Download Network resources

package com.volcano.net;

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

public class UrlDown {
    public static void main(String[] args) throws IOException {
        //1. Download address
        URL url = new URL("xxxxxxx");// Enter a valid resource URL
        2. Connect to the resource HTTP
        HttpURLConnection urlConnection=(HttpURLConnection)url.openConnection();

        InputStream inputStream = urlConnection.getInputStream();
        FileOutputStream outputStream=new FileOutputStream("a.txt");
        byte[] buffer=new byte[1024];
        int len;
        while((len=inputStream.read(buffer))! = -1){
            outputStream.write(buffer,0,len); } outputStream.close(); inputStream.close(); urlConnection.disconnect(); }}Copy the code