TCP socket connection

Question

I'm new to the network communication and I'm trying to build client-server application.

protected void init(){
    Server myServer = new Server();
    Client myClient = new Client();
}

That's my Client class:

public class Client {

public Client() {
    init();
}

private void init() {
    Socket echoSocket = null;
    DataOutputStream os = null;
    DataInputStream is = null;
    DataInputStream stdIn = new DataInputStream(System.in);

    try {
        echoSocket = new Socket("localhost", 1234);
        os = new DataOutputStream(echoSocket.getOutputStream());
        is = new DataInputStream(echoSocket.getInputStream());

        os.writeInt(stdIn.readInt());

        echoSocket.getOutputStream().close();
        echoSocket.getInputStream().close();
        echoSocket.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}
}

And that's server:

public class Server {

public Server() {
    init();
}

private void init() {
    try {
        boolean run = true;
        ServerSocket ss = new ServerSocket(1234);
        Socket s = ss.accept();
        DataInputStream dis = new DataInputStream(s.getInputStream());
        System.out.println(dis.readInt());
        s.getInputStream().close();
        s.getOutputStream().close();
        s.close();
    } catch (IOException e) {
        e.printStackTrace();
    }

}

}

First of all: Can I initialize client and server simply like i did? new Server() and new Client()?

Question 2: Is it important what i initialize at first? client or server?

Question 3: When i compile this code with client first initialized, i become Connection refused: connect. I know it means that there is no listening socket running on the port you are trying to connect to. That's why server must go first, i think. Is it so? can i fix it using setSoTimeout and how?

Question 4: When i compile it with server and then client, output is nothing. And i think it has nothing to do with client, because if i try to print "1", for example, it doesn't work either. I think it just waits for the client and does nothing that goes after. How can i fix this? maybe setSoTimeout goes here too?

Answer 1

Make two different projects, first run server than client. Server will write on console "Server started" than run client it will ask your name, type your name press ok . Your name will be sent to server and server will reply saying hello to you.

Here is server code

import java.net.*;
import java.io.*;
import javax.swing.*;
public class Server {
    public static void main(String[] args) {
        try{
            ServerSocket ss= new ServerSocket(2224);
            System.out.println("Serever started");
            while(true)
            {
                Socket s=ss.accept();
                InputStream is=s.getInputStream();
                InputStreamReader isr=new InputStreamReader(is);
                BufferedReader br=new BufferedReader(isr);
                OutputStream os=s.getOutputStream();
                PrintWriter pw=new PrintWriter(os);
                String name=br.readLine();
                String message="Hello "+name+"from server";
                pw.println(message);
                pw.flush();
            }
        }
        catch(Exception exp)
        {
        System.out.println("Excepttion occured");
        }
    }
}

Here is client code

import java.net.*;
import java.io.*;
import java.util.Scanner;
import javax.swing.*;
public class Client {
    public static void main(String[] args) throws IOException {
        Socket s=new Socket("localhost",2224);
        InputStream is=s.getInputStream();
        InputStreamReader isr=new InputStreamReader(is); 
        BufferedReader br=new BufferedReader(isr);
        OutputStream os=s.getOutputStream();
        PrintWriter pw=new PrintWriter(os,true);
        String message = JOptionPane.showInputDialog("Give your name");
        pw.println(message);
        pw.flush();
        String servermessage = br.readLine();
      JOptionPane.showMessageDialog(null, servermessage);
        s.close();
    }
}

Answer 2

You can't have both client and server in the same thread.

As you already have observed, the server accepts the connection and tries to read something. It doesn't know that the client is running in the very same thread.

Either make a multi-threaded application, where client and server have their own thread. Or make two prgrams that run independently of each other. The latter would be also the "normal case".