java network programming

Network Communications

1.1 Overview

Two major issues in network communication:

How to accurately locate one or more hosts on the network
How to communicate when a host is found

1.2 Elements of network communication

Address of both parties:

IP (ip class)
Port number (udp and tcp classes)

For example, 192.168.16.124:5900

Rule: Protocol for network communication

Everything is object

1.3 IP

ip address: InerAddress

Uniquely locate a host on a network
127.0.0.1: localhost
Classification of ip addresses
- ipv4/ipv6
  - ipv4 127.0.0.1, consisting of 4 bytes. 0-25.5 billion; 3 billion in North America, 400 million in Asia, and used up in 2011;
  - ipv6 128 bits, 8 unsigned integers for example: 2001:0bb2:aaaa:1150:0000:0000:bc21:0213
- Public (Internet) / Private (LAN)
  - ABCD Class Address
  - 192.168.xx.xx is intended for use within an organization
Domain name: Memory IP
- IP: Many IPs are no longer available and expensive to buy

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

//Test IP
public class TestInetAddress {
    public static void main(String[] args) {
        try {
            //Query local address
            InetAddress inetAddress1 = InetAddress.getByName("127.0.0.1");
            System.out.println(inetAddress1);
            InetAddress inetAddress2 = InetAddress.getByName("localhost");
            System.out.println(inetAddress2);
            InetAddress inetAddress3 = InetAddress.getLocalHost();
            System.out.println(inetAddress3);

            //Query ip address of website
            InetAddress inetAddress4 = InetAddress.getByName("www.baidu.com");
            System.out.println(inetAddress4);

            //common method
            //System.out.println(inetAddress4.getAddress());
            System.out.println(inetAddress4.getCanonicalHostName());//Specification name
            System.out.println(inetAddress4.getHostAddress());//ip
            System.out.println(inetAddress4.getHostName());//domain name


        } catch (UnknownHostException e) {
            e.printStackTrace();
        }
    }
}

1.4 Port

Ports represent the processes of a program on a computer;

Different processes have different port numbers! Used to differentiate software!
Provisioned 0-65535
TCP UDP:65535*2, port number can not conflict under a single protocol
Port Classification
- Public ports 0~1023
  - HTTP:80
  - HTTPS:443
  - FTP:21
  - Telent: 23
- Program registration ports: 1024~49151, assign users or programs
  - Tomcat: 8080
  - MySQL: 3306
  - Oracle: 1521
- Dynamic, Private: 19452~65535

netstat -ano #View all ports
netstat -ano|findstr "5900" #View the specified port
tasklisk|findstr '8696' #View processes on specified ports

import java.net.InetSocketAddress;

public class TestInetSockerAddress {
    public static void main(String[] args) {
        InetSocketAddress socketAddress = new InetSocketAddress("127.0.0.1", 8080);
        InetSocketAddress socketAddress2 = new InetSocketAddress("localhost", 8080);
        System.out.println(socketAddress);
        System.out.println(socketAddress2);

        System.out.println(socketAddress.getAddress());
        System.out.println(socketAddress.getHostName());//address
        System.out.println(socketAddress.getPort());//port
    }
}

1.5 Communication Protocol

Agreement: agreement, just like what we are talking about now is Mandarin

Network Communication Protocols: Rate, Transmit Bit Rate, Code Structure, Transport Control...Very Complex

Small things: layered!

TCP/IP protocol cluster: actually a set of protocols

Important:

TCP: User Transfer Protocol (Analogue Phone)
UDP: User Datagram Protocol (Similar SMS)

Famous agreements:

TCP: User Transfer Protocol
IP: Network Interconnect Protocol

TCP UDP comparison

TCP: Call

Connection Stable
Three handshakes, four waves

Require at least three times for a stable connection
A: What do you see?
B: Look at you!
A: Do a job

A: I am afraid that l have to go
B: Are you really going to leave?
B: Do you really want to go?
A: I really have to go!
(Essentially A Send out, B Accept; B Send out, A Receive)

Client, Server
Transfer complete, connection released, inefficient

UDP: Send text messages

Disconnected, unstable
Client, server: no clear boundaries
Send it to you whether you're ready or not (just like a missile launches, it doesn't inform the target)
DDOS: Flood attack! (Saturation Attack)

1.6 TCP

Client

Connect Server Socket
send message

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

//Client
public class TcpClientDemo01 {
    public static void main(String[] args) {
        Socket socket=null;
        OutputStream os=null;
        try {
            //1. To know the address and port number of the server
            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("Hello, welcome to my blog".getBytes());
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            if(os!=null){
                try {
                    os.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(socket!=null){
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }
}

The server

Set up a service's port ServerSocket
Waiting for user's connection accept
receive messages

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

//Server
public class TcpServerDemo01 {
    public static void main(String[] args) {
        ServerSocket serverSocket=null;
        Socket socket=null;
        InputStream is=null;
        ByteArrayOutputStream baos=null;
        try {
            //1. I have to have an address
            serverSocket = new ServerSocket(9999);
            //2. Wait for the customer to link in
            socket = serverSocket.accept();
            //3. Waiting for messages from clients
            is = socket.getInputStream();

            //Pipeline 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());

        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            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();
                }
            }

        }

    }

}

File Upload

Client

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

public class TcpClientDemo02 {
    public static void main(String[] args) throws Exception {
        //1. Create a socket connection
        Socket socket = new Socket(InetAddress.getByName("127.0.0.1"), 9000);
        //2. Create an output stream
        OutputStream os=socket.getOutputStream();
        //3. Read Files
        FileInputStream fis = new FileInputStream(new File("Head portrait.jpeg"));
        //4. Write out the file
        byte[] buffer = new byte[1024];
        int len;
        while((len=fis.read())!=-1){
            os.write(buffer,0,len);
        }

        //Last added: notify the server that I'm finished
        socket.shutdownOutput();//Notify the server that I have finished transferring

        //Confirm that the server has received before disconnecting
        InputStream inputStream = socket.getInputStream();
        //String byte[]
        ByteArrayOutputStream baos = new ByteArrayOutputStream();

        byte[] buffer2 = new byte[2014];
        int len2;
        while((len=inputStream.read(buffer2))!=-1){
            baos.write(buffer2,0,len);
        }

        System.out.println(baos.toString());

        //5. Close resources
        baos.close();
        inputStream.close();
        fis.close();
        os.close();
        socket.close();
    }
}

The server

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

public class TcpServerDemo02 {
    public static void main(String[] args) throws Exception {
        //1. Create a service
        ServerSocket serverSocket = new ServerSocket(9000);
        //2. Listen for client connections
        Socket socket = serverSocket.accept();
        //3. Get input stream
        InputStream is = socket.getInputStream();
        //4. File Output
        FileOutputStream fos = new FileOutputStream(new File("Receive.jpeg"));
        byte[] buffer = new byte[1024];
        int len;
        while((len=is.read())!=-1){
            fos.write(buffer,0,len);
        }

        //Notify client that I have finished receiving
        OutputStream os = socket.getOutputStream();
        os.write("I'm done. You can disconnect".getBytes());


        //5. Close resources
        fos.close();
        is.close();
        socket.close();
        serverSocket.close();
    }
}

Tomcat

Server

Custom S
Tomcat Server S: Java Background Development focuses on servers built with others!

Client

Custom C
Browser B

1.7 UDP

Text message: no connection, need to know each other's address

send message

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

//No need to connect to server
public class UdpClientDemo01 {
    public static void main(String[] args) throws Exception {
        //1. Create a socket
        DatagramSocket socket = new DatagramSocket();

        //2. Build a package
        String msg="Hello, server!";

        //To whom
        InetAddress localhost = InetAddress.getByName("localhost");
        int port=9090;
        DatagramPacket packet = new DatagramPacket(msg.getBytes(), 0, msg.getBytes().length, localhost, port);

        //3. Send Packets
        socket.send(packet);

        //4. Close the stream
        socket.close();

    }
}

receiving end

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

public class UdpServerDemo01 {
    public static void main(String[] args) throws IOException {
        //Open Port
        DatagramSocket socket = new DatagramSocket(9090);

        //Receive Packets
        byte[] buffer=new byte[1024];
        DatagramPacket packet = new DatagramPacket(buffer, 0, buffer.length);
        socket.receive(packet);
        System.out.println(packet.getAddress().getHostAddress());
        System.out.println(new String(packet.getData(),0,packet.getLength()));

        //Close Connection
        socket.close();
    }
}

Send message circularly

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;

public class UdpSenderDemo02 {
    public static void main(String[] args) throws Exception {
        DatagramSocket socket = new DatagramSocket();

        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        while(true){
            String data=reader.readLine();
            byte[] datas=data.getBytes();
            DatagramPacket packet = new DatagramPacket(datas, 0, data.length(), new InetSocketAddress("localhost", 6666));
            socket.send(packet);

            if(data.equals("bye")){
                break;
            }
        }


        socket.close();
    }
}

Receive messages in a loop

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

public class UdpReceiveDemo02 {
    public static void main(String[] args) throws Exception {
        DatagramSocket socket = new DatagramSocket(6666);

        while(true){
            byte[] container = new byte[1024];
            DatagramPacket packet = new DatagramPacket(container, 0, container.length);
            socket.receive(packet);

            byte[] data = packet.getData();
            String receiveData= new String(data,0,data.length);
            System.out.println(receiveData);
            if(receiveData.equals("bye")){
                break;
            }

        }

        socket.close();
    }
}

Online Consulting

There are four parts: receiving, sending, teacher, student, two people can be either sender or receiver

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;

public class TalkSend implements Runnable{
    DatagramSocket socket =null;
    BufferedReader reader =null;

    private int fromPort;
    private String toIP;
    private int toPort;

    public TalkSend(int fromPort, String toIP, int toPort) {
        this.fromPort = fromPort;
        this.toIP = toIP;
        this.toPort = toPort;

        try{
            socket = new DatagramSocket(fromPort);
            reader = new BufferedReader(new InputStreamReader(System.in));
        }catch(Exception e){
            e.printStackTrace();
        }
    }

    @Override
    public void run() {

        while(true){
            try{
                String data=reader.readLine();
                byte[] datas=data.getBytes();
                DatagramPacket packet1 = new DatagramPacket(datas, 0, datas.length, new InetSocketAddress(this.toIP,this.toPort));

                socket.send(packet1);

                if(data.equals("bye")){
                    break;
                }
            }catch(Exception e){
                e.printStackTrace();
            }
        }
        socket.close();
    }
}

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

public class TalkReceive implements Runnable {
    DatagramSocket socket = null;

    private int port;
    private String msgFrom ;

    public TalkReceive(int port, String msgFrom) {
        this.port = port;
        this.msgFrom = msgFrom;
        try {
            socket = new DatagramSocket(port);
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    @Override
    public void run() {

        while (true) {
            try {
                byte[] container = new byte[1024];
                DatagramPacket packet = new DatagramPacket(container, 0, container.length);
                socket.receive(packet);

                byte[] data = packet.getData();
                String receiveData = new String(data, 0, data.length);

                System.out.println(msgFrom + ":" + receiveData);

                if (receiveData.equals("bye")) {
                    break;
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        socket.close();
    }
}

public class TalkStudent {
    public static void main(String[] args) {
        //Open two threads
        new Thread(new TalkSend(5555,"localhost",9999)).start();
        new Thread(new TalkReceive(8888,"Teacher")).start();
    }
}

public class TalkTeacher {
    public static void main(String[] args) {
        new Thread(new TalkSend(3333,"localhost",8888)).start();
        new Thread(new TalkReceive(9999,"Student")).start();
    }
}

1.8 URL

https://www.baidu.com/

Uniform Resource Locator: Locating a resource or a resource on the Internet

Protocol: // ip address: port/project name/resource

Tags: Java Network Communications

Posted by ugh82 on Tue, 05 Apr 2022 20:20:50 +0300

Algorithm Zone

java network programming

Network Communications

1.1 Overview

1.2 Elements of network communication

1.3 IP

1.4 Port

1.5 Communication Protocol

1.6 TCP

File Upload

Tomcat

1.7 UDP

send message

receiving end

Send message circularly

Receive messages in a loop

Online Consulting

1.8 URL

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