Java DatagramSocket 無連線通訊實作指南（下）

DatagramSocket 類別

DatagramSocket 用於 UDP 通訊。客戶端用無參數建構子繫結任意埠口；伺服器端用 DatagramSocket(int port) 繫結固定埠口。失敗拋出 SocketException。

核心方法

• send(DatagramPacket)：發送資料包
• receive(DatagramPacket)：接收資料包（阻塞）

客戶端範例：DGSClient

DatagramSocket socket = new DatagramSocket();
byte[] buffer = "Send me a datagram".getBytes();
InetAddress ia = InetAddress.getByName("localhost");
DatagramPacket packet = new DatagramPacket(buffer, buffer.length, ia, 10000);
socket.send(packet);

byte[] recvBuf = new byte[100];
DatagramPacket recvPacket = new DatagramPacket(recvBuf, recvBuf.length, ia, 10000);
socket.receive(recvPacket);
System.out.println(new String(recvPacket.getData()));
socket.close();

伺服器端範例：DGSServer

DatagramSocket socket = new DatagramSocket(10000);
byte[] data = new byte[100];
DatagramPacket packet = new DatagramPacket(data, data.length);
while (true) {
    socket.receive(packet);
    System.out.println(new String(data));
    socket.send(packet); // 回應
}

執行步驟

1. 先啟動伺服器：java DGSServer
2. 再啟動客戶端：java DGSClient（跨主機時加主機名/IP）

關鍵差異：UDP vs TCP