客户端：

public class Client {
	private int port = 8000;
	private String host = "localhost";
	private Socket socket;

	public Client() throws UnknownHostException, IOException {
		socket = new Socket(host, port);
	}

	public void readFromUser() throws IOException{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String line;
		while((line = br.readLine()) != null){
			if(line.equals("bye")){
				socket.close();
				System.out.println("关闭socket");
				break;
			}
			send(line);
		}
	}
	
	public void send(String msg) throws IOException {
		PrintWriter pw = new PrintWriter(socket.getOutputStream(), true);
		pw.println(msg);
	}

	public static void main(String args[]) throws UnknownHostException,
			IOException {
		new Client().readFromUser();
	}
}

public class Server {
	private int port = 8000;
	private ServerSocket serverSocket;
	private ExecutorService executorService;
	private final int POOL_SIZE = 4;

	public Server() throws IOException {
		serverSocket = new ServerSocket(port, 2);
		// 创建线程池
		executorService = Executors.newFixedThreadPool(Runtime.getRuntime()
				.availableProcessors()
				* POOL_SIZE);
		System.out.println("服务器启动。。。。。" + "初始线程数："
				+ Runtime.getRuntime().availableProcessors() * POOL_SIZE);
	}

	public void service() throws IOException {
		int count = 0;
		while (true) {
			Socket socket = serverSocket.accept();
			System.out.println(++count + "客户端已链接");
			// new Thread(new Handler(socket)).start();
			executorService.execute(new Handler(socket));
		}
	}

	public static void main(String args[]) throws IOException {
		new Server().service();
	}

	private class Handler implements Runnable {

		private Socket socket;

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

		public void run() {
			try {
				handle();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}

		private void handle() throws IOException {
			BufferedReader br = new BufferedReader(new InputStreamReader(socket
					.getInputStream()));
			String line;
			while ((line = br.readLine()) != null) {
				if(line.equals("goodbye")){
					socket.close();
					serverSocket.close();
					break;
				}
				System.out.println("From " + socket.getPort() + ":" + line);
			}
		}
	}
}

还可以使用NIO来实现，即非阻塞通信