NIO系列（五）——Udp协议(DatagramChannel)

阳光穿透心脏的1/2处 2022-06-13 02:15 178阅读 0赞

## DatagramChannel ##

DatagramChannel是收发UDP包的通道，与TCP协议不同，UDP发送不进行连接，也不对确认数据是否收到。

### 打开DatagramChannel ###

DatagramChannel server = DatagramChannel.open();
    server.socket().bind(newInetSocketAddress(10086));

此例子是打开10086端口接收udp数据包

### 接收数据 ###

通过receive()接收udp包

ByteBuffer receiveBuffer = ByteBuffer.allocate(64);
    receiveBuffer.clear();
    SocketAddress receiveAddr = server.receive(receiveBuffer);

SocketAddress可以获得发包的ip、端口等信息，用toString查看，格式如下

/127.0.0.1:57126

### 发送数据 ###

通过send()发送udp包

DatagramChannel server = DatagramChannel.open();
    ByteBuffer sendBuffer = ByteBuffer.wrap("client send".getBytes());
    server.send(sendBuffer, new InetSocketAddress("127.0.0.1",10086));

### 连接 ###

udp不存在真正意义上的连接，这里的连接是向特定服务地址用read和write接收发送数据包。

client.connect(new InetSocketAddress("127.0.0.1",10086));
    int readSize= client.read(sendBuffer);
    server.write(sendBuffer);

read()和write()只有在connect()后才能使用，不然会抛NotYetConnectedException异常。用read()接收时，如果没有接收到包，会抛PortUnreachableException异常。

### 例子 ###

客户端发送，服务端接收的例子

/**
     * 发包的datagram
     *
     * @throws IOException
     * @throws InterruptedException
     */
    @Test
    public voidsendDatagram() throwsIOException, InterruptedException {
        DatagramChannelsendChannel= DatagramChannel.open();
        InetSocketAddresssendAddress= newInetSocketAddress("127.0.0.1", 9999);
        while (true) {
           sendChannel.send(ByteBuffer.wrap("发包".getBytes("UTF-8")), sendAddress);
           System.out.println("发包端发包");
           Thread.sleep(1000);
        }
    }
     
    /**
     * 收包端
     *
     * @throws IOException
     */
    @Test
    public voidreceive() throwsIOException {
        DatagramChannelreceiveChannel= DatagramChannel.open();
        InetSocketAddressreceiveAddress= newInetSocketAddress(9999);
        receiveChannel.bind(receiveAddress);
        ByteBufferreceiveBuffer= ByteBuffer.allocate(512);
        while (true) {
           receiveBuffer.clear();
           SocketAddresssendAddress= receiveChannel.receive(receiveBuffer);
           receiveBuffer.flip();
           System.out.print(sendAddress.toString() + " ");
           System.out.println(Charset.forName("UTF-8").decode(receiveBuffer));
        }
    }
     
    /**
     * 只接收和发送9999的数据包
     *
     * @throws IOException
     */
    @Test
    public voidtestConect1() throwsIOException {
        DatagramChannelconnChannel= DatagramChannel.open();
        connChannel.bind(newInetSocketAddress(9998));
        connChannel.connect(new InetSocketAddress("127.0.0.1",9999));
        connChannel.write(ByteBuffer.wrap("发包".getBytes("UTF-8")));
        ByteBufferreadBuffer= ByteBuffer.allocate(512);
        while (true) {
           try {
               readBuffer.clear();
               connChannel.read(readBuffer);
               readBuffer.flip();
               System.out.println(Charset.forName("UTF-8").decode(readBuffer));
           }catch(Exception e) {
     
           }
        }
    }
     
    /**
     * 只接收和发送9998的数据包
     *
     * @throws IOException
     */
    @Test
    public voidtestConect2() throwsIOException {
        DatagramChannelconnChannel= DatagramChannel.open();
        connChannel.bind(newInetSocketAddress(9999));
        connChannel.connect(new InetSocketAddress("127.0.0.1",9998));
        while (true) {
           connChannel.write(ByteBuffer.wrap("发包".getBytes("UTF-8")));
           System.out.println("发包成功");
        }
    }