Client

/*
 * Java socket programming client example with TCP
 * socket programming at the client side, which provides example of how to define client socket, how to send message to
 * the server and get response from the server with DataInputStream and DataOutputStream
 *
 * Author: Wei Song
 * Date: 2021-09-28
 * */


import java.net.*;
import java.io.*;


public class TCPClient {
    // server host and port number, which would be acquired from command line parameter
    private static String serverHost;
    private static Integer serverPort;

    public static void main(String[] args) throws IOException {
        if (args.length != 2) {
            System.out.println("===== Error usage: java TCPClient SERVER_IP SERVER_PORT =====");
            return;
        }

        serverHost = args[0];
        serverPort = Integer.parseInt(args[1]);

        // define socket for client
        Socket clientSocket = new Socket(serverHost, serverPort);

        // define DataInputStream instance which would be used to receive response from the server
        // define DataOutputStream instance which would be used to send message to the server
        DataInputStream dataInputStream = new DataInputStream(clientSocket.getInputStream());
        DataOutputStream dataOutputStream = new DataOutputStream(clientSocket.getOutputStream());

        // define a BufferedReader to get input from command line i.e., standard input from keyboard
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        while (true) {
            System.out.println("===== Please input any message you want to send to the server: ");

            // read input from command line
            String message = reader.readLine();

            // write message into dataOutputStream and send/flush to the server
            dataOutputStream.writeUTF(message);
            dataOutputStream.flush();
            // receive the server response from dataInputStream
            String responseMessage = (String) dataInputStream.readUTF();
            System.out.println("[recv] " + responseMessage);

            System.out.println("Do you want to continue(y/n) :");
            String answer = reader.readLine();
            if (answer.equals("n")) {
                System.out.println("Good bye");
                clientSocket.close();
                dataOutputStream.close();
                dataInputStream.close();
                break;
            }
        }
    }
}