EchoServer

package coozplz.example;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.logging.Level;
import java.util.logging.Logger;

public class MultiThreadEchoServerMain extends Thread {
    public static void main(String[] args) throws IOException {
        ServerSocket ss = new ServerSocket(9999);
        System.out.println("서버 소켓 생성 완료");

        while (true) {
            Socket sock = ss.accept();
            System.out.println(sock.getInetAddress().toString() + " // is connted");
            MultiThreadEchoServer client = new MultiThreadEchoServer(sock);
            client.start();


        }

    }
}

class MultiThreadEchoServer extends Thread {
    Socket socket;
    InputStream in;
    OutputStream os;

    public MultiThreadEchoServer(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {
        System.out.println("MultiThreadEchoServer is Running");
        try {
            in = socket.getInputStream();
            os = socket.getOutputStream();


            byte[] buf = new byte[1024];
            int count;
            while ((count = in.read(buf)) > 0) {

                System.out.println("received: " + new String(buf, 0, count));
                os.write(buf, 0, count);
                System.out.println("write:" + new String(buf, 0, count));
            }
            os.close();
            System.out.println("연결종료");
        } catch (IOException ex) {
            Logger.getLogger(MultiThreadEchoServerMain.class.getName()).log(Level.SEVERE, null, ex);
        } finally {
            if (socket != null) {
                try {
                    socket.close();
                } catch (IOException ex) {
                    Logger.getLogger(MultiThreadEchoServerMain.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        }
    }


}

Echo Client

package coozplz.example;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.net.Socket;

public class EchoClientThread {
    public static void main(String[] ar) throws IOException {
        EchoClientThread client = new EchoClientThread();
        client.process();
    }

    public void process() throws IOException {
        Socket socket = new Socket();
        socket.connect(new InetSocketAddress("127.0.0.1", 9999));
        OutputStream os = socket.getOutputStream();
        InputStream in = socket.getInputStream();


        byte[] buf = new byte[1024];
        int count = 0;
        while ((count = System.in.read(buf)) > 0) {
            os.write(buf, 0, count);
            System.out.println("Client -> Svr: " + new String(buf, 0, count));
            count = in.read(buf);
            System.out.println("Svr -> Client: " + new String(buf, 0, count));
        }
        os.close();
        while ((count = in.read(buf)) > 0) {
            System.out.write(buf, 0, count);
        }
        System.out.close();
        System.out.println("연결종료");
        if (socket != null) {
            socket.close();
        }
    }
}