Java Socket Programming dealing with only byte arrays as in/output data using thread pool

Client.java

package test_socket;

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

/**
 * up to 3 clients can access simultaneously and the others have to queue.
 * 
 * 
 * @author Serae Kim
 *
 */
public class Client implements Runnable {
	Thread thread;
	Socket s;
	InputStream in;
	OutputStream out;

	public Client() {
		if (connect()) {
			try {
				System.out.println("고객접속");
				// 0: protocol, -55: data
				out.write(new byte[]{0,-55});
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}

	public static void main(String[] args) {
		new Client();
	}

	@Override
	public void run() {
		boolean isContinued = true;
		while (isContinued) {
			byte[] protocol = new byte[1];
			try {
				int isValid = in.read(protocol);
				byte msg = -100;

				if (isValid > 0) {
					switch (protocol[0]) {
					case 100:
						// get client no
						msg = (byte) in.read();
						System.out.println("client 100|" + msg);
						out.write(new byte[] { 1, 2, 3, 4, 5});
						break;
					case 101:
						msg = (byte) in.read();
						System.out.println("client 101|" + msg);
						// 2 means notifying close to the server
						try {
							Thread.sleep(10000);
						} catch (InterruptedException e) {
							e.printStackTrace();
						}
						out.write(new byte[] { 2 });
						isContinued = false;
						System.out.println("client end");
						break;
					}
						
				}

			} catch (IOException e) {
				e.printStackTrace();
			}
		}
		try {
			if (out != null) {
				out.close();
			}
			if (in != null) {
				in.close();
			}
			if (s != null) {
				s.close();
			}

		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	boolean connect() {
		try {
			s = new Socket("localhost", 10000);
			in = s.getInputStream();
			out = s.getOutputStream();
			thread = new Thread(this);
			thread.start();
		} catch (UnknownHostException e) {
			e.printStackTrace();
			return false;
		} catch (IOException e) {
			e.printStackTrace();
		}

		return true;
	}
}

ClientCopy.java

package test_socket;

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

/**
 * Dealing with multiple client objects from server side
 * playing a role of interface for clients and server
 *
 * @author Serae Kim
 *
 */
public class ClientCopy implements Runnable {

	static int count = 0;
	int clientNo = 0;
	
	Socket s;
	InputStream in;
	OutputStream out;
	Server server;
	
	public ClientCopy(Socket s, Server server) {
		this.s = s;
		this.server = server;
		this.clientNo = ++count;
		try {
			in = s.getInputStream();
			out = s.getOutputStream();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
	
	@Override
	public void run() {

		boolean isContinued = true;
		while (isContinued) {
			byte[] protocol = new byte[1];
			try {
				int isValid = in.read(protocol);
				byte msg = -100;
				if (isValid > 0) {
					switch (protocol[0]) {
					// client connect
					case 0:
						server.addClient(this);
						// should be -55
						msg = (byte) in.read();
						System.out.println("server 0|" + msg);
						// send -55
						out.write(new byte[] { 100, msg });
						break;
					case 1:
						// 2
						msg = (byte) in.read();
						System.out.println("server 1|" + msg);
						out.write(new byte[] { 101, msg });
						break;
					// get 2 and remove the client from the client pool.
					case 2:
						System.out.println("server 2| 종료");
						// 서버로부터 종료처리.
						server.removeClient(this);
						isContinued = false;
						break;
					}
				}

			} catch (IOException e) {
				// if socket is closed abruptly, remove it from client pool.
				server.removeClient(this);
				isContinued = false;
			}
		}
		try {
			if (out != null) {
				out.close();
			}
			if (in != null) {
				in.close();
			}
			if (s != null) {
				s.close();
			}

		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

Server.java

package test_socket;

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Server implements Runnable {
	// java socketserver serves 50 ports as default.
	// can modify the number of ports using Executor
	ExecutorService threadPool = Executors.newFixedThreadPool(3);
	int port = 10000;
	ServerSocket ss;
	List<ClientCopy> list;
	
	public static void main(String[] args) {
		new Thread(new Server()).start();
	}

	public Server() {
		try {
			ss = new ServerSocket(port);
			list = new ArrayList<ClientCopy>();
			System.out.println("server start!");
		} catch(Exception e) {
			e.printStackTrace();
		}
	}
	
	@Override
	public void run() {
		while (true) {
			try {
				// waiting for client connection
				Socket s = ss.accept();
				threadPool.execute(new ClientCopy(s, this));
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
	
	public void addClient(ClientCopy cc) { // to update client list
		list.add(cc);
		
		System.out.println("고객"+cc.clientNo+" 접속==========");
		System.out.println("동시접속인원:" + list.size());
	}
	
	public void removeClient(ClientCopy cc) {
		System.out.println("고객"+cc.clientNo+" 퇴장============");
		list.remove(cc);
		System.out.println("동시접속인원:" + list.size());
	}
}