4.7 UDP

• UDP 是无连接的，client 发送数据不会管 server 是否开启
• server 这边的 receive 方法会将接收到的数据存入 byte buffer，但如果数据报文超过 buffer 大小，多出来的数据会被默默抛弃

首先启动服务器端

public class UdpServer { public static void main(String[] args) { try (DatagramChannel channel = DatagramChannel.open()) { channel.socket().bind(new InetSocketAddress(9999)); System.out.println("waiting..."); ByteBuffer buffer = ByteBuffer.allocate(32); channel.receive(buffer); buffer.flip(); debug(buffer); } catch (IOException e) { e.printStackTrace(); } } }

运行客户端 public class UdpClient { public static void main(String[] args) { try (DatagramChannel channel = DatagramChannel.open()) { ByteBuffer buffer = StandardCharsets.UTF_8.encode("hello"); InetSocketAddress address = new InetSocketAddress("localhost", 9999); channel.send(buffer, address); } catch (Exception e) { e.printStackTrace(); } } }