NIO 03 DatagramChannel

1、API

⑴ 数据报通道

    DatagramChannel.open();

    获取数据包通道实例

⑵ 切换为非阻塞模式

    configureBlocking(false);

⑶ 设置key上的通道的监听模式

    register(Selector sel, int ops);

    第一个参数为选择器；第二个参数为SelectionKey的监听模式

        SelectionKey.OP_READ = 1 读

        SelectionKey.OP_WRITE = 4 写

        SelectionKey.OP_CONNECT = 8 连接

        SelectionKey.OP_ACCEPT =16 接收

⑷ 发送数据报

    send(ByteBuffer src, SocketAddress target);

    第一个为字节缓冲区；第二个参数为要发送的地址，使用InetSocketAddress(String hostname, int port)即可

⑸ 接收数据报

    receive(ByteBuffer dst);

    将接收到的数据报，复制到指定的字节缓冲区中

⑹ 绑定端口

    bind(SocketAddress local);

    使用InetSocketAddress(int port)即可

2、接收端

DatagramChannel receiver = null;
    try {
        receiver = DatagramChannel.open();
        receiver.bind(new InetSocketAddress(???));
        receiver.configureBlocking(false); // 切换为非阻塞式

        Selector selector = Selector.open();
        receiver.register(selector, SelectionKey.OP_READ); // 监听键上的通道的读取模式

        while (0 < selector.select()) {
            Set<SelectionKey> selectionKeys = selector.selectedKeys();
            Iterator<SelectionKey> iterator = selectionKeys.iterator();
            SelectionKey selectionKey;
            ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
            while (iterator.hasNext()) {
                selectionKey = iterator.next();
                if (selectionKey.isReadable()) {
                    receiver.receive(byteBuffer);
                    byteBuffer.flip();
                    System.out.println(new String(byteBuffer.array(), 0, byteBuffer.limit()));
                    byteBuffer.clear();
                }
                iterator.remove(); // 移除选择器的监听，否则一旦接收到消息，会停止程序的
            }
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (null != receiver) {
            try {
                receiver.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
           

3、发送端

DatagramChannel sender = null;
    Scanner scanner = null;
    try {
        sender = DatagramChannel.open();
        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
        sender.configureBlocking(false); // 切换为非阻塞模式
        scanner = new Scanner(System.in);
        while (scanner.hasNext()) {
            String next = scanner.nextLine();
            byteBuffer.put(next.getBytes());
            byteBuffer.flip();
            sender.send(byteBuffer, new InetSocketAddress("???.???.???.???", ???));
            byteBuffer.clear();
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (null != scanner) {
            scanner.close();
        }
        if (null != sender) {
            try {
                sender.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }