package apibook.c5.s1;import java.net.*;import java.io.*;//測試DatagramSocket類class EchoServer extends Thread {    private DatagramSocket sock = null;    EchoServer(int port) {        try {//建立數據包socket            sock = new DatagramSocket(port);        } catch (SocketException e) {            e.printStackTrace();        }    }    public void run() {        if (sock == null)            return;//如果socket沒有建立，則返回        byte[] inbuf = new byte[1024];//緩沖區        DatagramPacket request = new DatagramPacket(inbuf, inbuf.length);        try {            while (true) {//循環收發                sock.receive(request);//接收                sock.send(request);//發送            }        } catch (IOException e) {            e.printStackTrace();        }    }}public class TestDatagramSocket {  static int echo_port = 1234;  public TestDatagramSocket() {  }public static void echo(String msg, DatagramSocket client) {  byte[] inbuf = new byte[1024];  // 緩沖區  byte[] outbuf = msg.getBytes(); //發送的內容  try {      DatagramPacket request = new DatagramPacket(outbuf, outbuf.length);      DatagramPacket reply = new DatagramPacket(inbuf, inbuf.length);      client.send(request);//發送      client.receive(reply);//接收      client.close();//關閉      System.out.println(new String(reply.getData()));//輸出接收的結果  } catch (SocketException e) {      e.printStackTrace();  } catch (IOException e) {      e.printStackTrace();  }}  public static void main(String[] args) {    String msg= "";    if (args.length != 1) {        msg = "test for DatagarmSocket";    }    else      msg = args[0];    //開始    EchoServer srv = new EchoServer(echo_port);    srv.setDaemon(true);    srv.start();    try {        InetAddress dst = InetAddress.getLocalHost();        DatagramSocket dest = new DatagramSocket();        dest.connect(dst, echo_port);        System.out.println("remote addr: " + dest.getInetAddress());        System.out.println("remote port: " + dest.getPort());        echo(msg, dest);        dest.disconnect();        System.out.println("disconnected addr: " + dest.getInetAddress());        System.out.println("disconnected port: " + dest.getPort());    } catch (UnknownHostException e) {        System.err.println("Host not found: " + e);    } catch (SocketException e) {        e.printStackTrace();    }  }}