请使用Nio优化上面的代码

以下是使用NIO优化的代码：

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class NioServer {
    private static final int PORT = 8888;
    private static final int BUFFER_SIZE = 1024;

    public static void main(String[] args) {
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        try {
            ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
            serverSocketChannel.socket().bind(new InetSocketAddress(PORT));
            while (true) {
                SocketChannel socketChannel = serverSocketChannel.accept();
                executorService.submit(() -> {
                    try {
                        ByteBuffer buffer = ByteBuffer.allocate(BUFFER_SIZE);
                        while (socketChannel.read(buffer) != -1) {
                            buffer.flip();
                            socketChannel.write(buffer);
                            buffer.clear();
                        }
                    } catch (IOException e) {
                        e.printStackTrace();
                    } finally {
                        try {
                            socketChannel.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                });
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

上述代码中，使用了`ServerSocketChannel`和`SocketChannel`代替了原来的`ServerSocket`和`Socket`，并且使用了`ByteBuffer`来进行数据的读写。同时，使用了线程池来处理客户端连接，避免了每个连接都创建一个新线程的问题。