Multiple client to server communication program in Java

Question

I wrote a server-client communication program and it worked well.

Client module

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

class Client {
    public static void main(String argv[]) throws Exception {
        String sentence;
        String modifiedSentence;
      while(true){
        BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));

        Socket clientSocket = new Socket("myname.domain.com", 2343);

        DataOutputStream out = new DataOutputStream(clientSocket.getOutputStream());
        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

        System.out.println("Ready");
        sentence = in.readLine();
        out.writeBytes(sentence + '\n');
        modifiedSentence = in.readLine();
        System.out.println(modifiedSentence);
       }
      clientSocket.close();
    }
}

Server module

import java.net.*;

public class Server {
    public static void main(String args[]) throws Exception {
        String clientSentence;
        String cap_Sentence;
        ServerSocket my_Socket = new ServerSocket(2343);

        while(true) {
            Socket connectionSocket = my_Socket.accept();
            BufferedReader in = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
            DataOutputStream out = new DataOutputStream(connectionSocket.getOutputStream());
            clientSentence = in.readLine();
            cap_Sentence = "Raceived:" +  clientSentence + '\n';
            out.writeBytes(cap_Sentence);
        }
    }
}

The above is the code for a single client - server communication, now I want multiple client to interact with that server. I googled for it and found that it can be done with the use of a thread for each single client to talk to the server, but since I am a beginner I don't know exactly how to implement. So somebody please tell me how to do or give me some idea about it.

Answer 1

MainServer class

public class Server {

    public static void main(String[] args) throws IOException {

        ServerSocket serverSocket = null;

        boolean listeningSocket = true;
        try {
            serverSocket = new ServerSocket(2343);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 2343");
        }

        while(listeningSocket){
            Socket clientSocket = serverSocket.accept();
            MiniServer mini = new MiniServer(clientSocket);
            mini.start();
        }
        serverSocket.close();       
    }

}

Helper Class

public class MiniServer extends Thread{

    private Socket socket = null;

    public MiniServer(Socket socket) {

        super("MiniServer");
        this.socket = socket;

    }

    public void run(){
            //Read input and process here
    }
            //implement your methods here

}

Answer 2

You want to look into Java concurrency. That's the concept of one Java program doing multiple things at once. At a high level you will be taking your while(true) { //... } block and running it as part of the run() method of a class implementing Runnable. You'll create instances of Thread that invoke that run() method, probably one per client you expect.

For a really good, deep understanding of all that Java offers when it comes to concurrency, check out Java Concurrency in Practice.