复习 AIO 写的小 Demo
涉及到两个核心类：1. AsynchronousServerSocketChannel 2. AsynchronousSocketChannel

服务端

public class SimpleAIOServer
{
    static final int PORT = 30000;
    public static void main(String[] args)
        throws Exception
    {
        try(
            // ①创建AsynchronousServerSocketChannel对象。
            AsynchronousServerSocketChannel serverChannel =
                AsynchronousServerSocketChannel.open())
        {
            // ②指定在指定地址、端口监听。
            serverChannel.bind(new InetSocketAddress(PORT));
            while (true)
            {
                // ③采用循环接受来自客户端的连接
                Future<AsynchronousSocketChannel> future
                    = serverChannel.accept();
                // 获取连接完成后返回的AsynchronousSocketChannel
                AsynchronousSocketChannel socketChannel = future.get();
                // 执行输出。
                socketChannel.write(ByteBuffer.wrap("欢迎你来自AIO的世界！"
                    .getBytes("UTF-8"))).get();
            }
        }
    }
}

客户端

public class SimpleAIOClient
{
    static final int PORT = 30000;
    public static void main(String[] args)
        throws Exception
    {
        // 用于读取数据的ByteBuffer。
        ByteBuffer buff = ByteBuffer.allocate(1024);
        Charset utf = Charset.forName("utf-8");
        try(
            // ①创建AsynchronousSocketChannel对象
            AsynchronousSocketChannel clientChannel
                = AsynchronousSocketChannel.open())
        {
            // ②连接远程服务器
            clientChannel.connect(new InetSocketAddress("127.0.0.1", PORT)).get();     // ④
            buff.clear();
            // ③从clientChannel中读取数据
            clientChannel.read(buff).get();     // ⑤
            buff.flip();
            // 将buff中内容转换为字符串
            String content = utf.decode(buff).toString();
            System.out.println("服务器信息：" + content);
        }
    }
}