Client.java

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

public class Client {
    private static Socket socket;
    private static InputStream is;
    private static OutputStream os;

    public static void main(String[] args) {
        try {

            // socket = new Socket("localhost", 5001);

            socket = new Socket();
            System.out.println("Server Connecting..");
            socket.connect(new InetSocketAddress("localhost", 2000));
            System.out.println("Server Connection OK!");

            is = socket.getInputStream();
            os = socket.getOutputStream();

            byte[] byteArr = null;
            String msg = "Hello Server";

            byteArr = msg.getBytes("UTF-8");
            os.write(byteArr);
            os.flush();
            System.out.println("Data Transmitted OK!");

            byteArr = new byte[512];
            int readByteCount = is.read();

            if(readByteCount == -1)
                throw new IOException();

            msg = new String(byteArr, 0, readByteCount, "UTF-8");
            System.out.println("Data Received OK!");
            System.out.println("Message : " + msg);

            is.close();
            os.close();

        } catch (UnknownHostException e) {
            // TODO Auto-generated catch block
            // IP Address가 잘못되었을 경우
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            // 해당 Port의 Server로 연결할 수 없는 경우
            e.printStackTrace();
            try { socket.close(); } catch (IOException e1) { e1.printStackTrace(); }
        }

        if(!socket.isClosed()) {
            try {
                socket.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}