Java NIO 由以下几个核心部分组成：
Channels
Buffers
Selectors
此系列的文章参考并发变成网的内容 http://ifeve.com/overview/
还有我同事写的几篇文章 https://www.jianshu.com/p/12c81abb5387

下面是socket通信的例子

public static class ClientSocket implements Runnable {
        public void run() {
            try {
               //SocketChannel的打开方式
                SocketChannel socketChannel = SocketChannel.open();
                socketChannel.connect(new InetSocketAddress("127.0.0.1", 9999));
                String newData = "New String to write to file..." + System.currentTimeMillis();
                ByteBuffer buf = ByteBuffer.allocate(48);//分配48字节capacity的ByteBuffer
                buf.clear();//情况buffer，进行写入
                buf.put(newData.getBytes());//buffer添加内容
                buf.flip();//执行此方法，使buffer进入读状态
                while (buf.hasRemaining()) {//判断buffer是不是读取完
                    socketChannel.write(buf);//将buffer内容读取到channel中
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public static class ServerSocket implements Runnable {
        public void run() {
            ServerSocketChannel serverSocketChannel;
            try {
                serverSocketChannel = ServerSocketChannel.open();//打开socket服务端
                serverSocketChannel.socket().bind(new InetSocketAddress(9999));
                //ServerSocketChannel可以设置成非阻塞模式。在非阻塞模式下，accept() 方法会立刻返回，如果还没有新进来的连接,返回的将是null
                //serverSocketChannel.configureBlocking(false);
                while (true) {
                     //监听新进来的连接
                    SocketChannel socketChannel = serverSocketChannel.accept();
                    ByteBuffer buf = ByteBuffer.allocate(48);
                    int bytesRead = socketChannel.read(buf);将通道信息写入buffer
                    while (bytesRead != -1) {//读取buffer
                        System.out.println("Read " + bytesRead);
                        buf.flip();
                        while (buf.hasRemaining()) {
                            System.out.print((char) buf.get());
                        }
                        buf.clear();
                        bytesRead = socketChannel.read(buf);
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }