package Socket;import java.net.DatagramPacket;import java.net.InetAddress;public class Dgram {    public static DatagramPacket toDatagram(String s, InetAddress destIA,            int destPort) {        byte[] buf = new byte[s.length() + 1];        s.getBytes(0, s.length(), buf, 0);        return new DatagramPacket(buf, buf.length, destIA, destPort);    }    public static String toString(DatagramPacket p) {        return new String(p.getData(), 0, p.getLength());    }}

package Socket;import java.io.IOException;import java.net.DatagramPacket;import java.net.DatagramSocket;import java.net.SocketException;public class ChatterServer {    static final int INPORT = 1712;    private byte[] buf = new byte[1000];    private DatagramPacket dp = new DatagramPacket(buf, buf.length);    private DatagramSocket socket;    public ChatterServer() {        try {            socket = new DatagramSocket(INPORT);// 创建一接收消息的对象，而不是每次接收消息都创建一个            System.out.println("Server started");            while (true) {                socket.receive(dp);                //接收到客户端的消息                String rcvd = Dgram.toString(dp) + ",from address:"                        + dp.getAddress() + ",port:" + dp.getPort();                System.out.println("From Client:"+rcvd);                                String echoString = "From Server Echoed:" + rcvd;                DatagramPacket echo = Dgram.toDatagram(echoString,                        dp.getAddress(), dp.getPort());                //将数据包发送给客户端                socket.send(echo);            }        } catch (SocketException e) {            System.err.println("Can‘t open socket");            System.exit(1);        } catch (IOException e) {            System.err.println("Communication error");            e.printStackTrace();        }    }    public static void main(String[] args) {        new ChatterServer();    }}

package Socket;import java.io.IOException;import java.net.DatagramPacket;import java.net.DatagramSocket;import java.net.InetAddress;import java.net.SocketException;import java.net.UnknownHostException;public class ChatterClient extends Thread {    private DatagramSocket s;    private InetAddress hostAddress;    private byte[] buf = new byte[1000];    private DatagramPacket dp = new DatagramPacket(buf, buf.length);    private int id;    public ChatterClient(int identifier) {        id = identifier;        try {            s = new DatagramSocket();            hostAddress = InetAddress.getByName("localhost");        } catch (UnknownHostException e) {            System.err.println("Cannot find host");            System.exit(1);        } catch (SocketException e) {            System.err.println("Can‘t open socket");            e.printStackTrace();            System.exit(1);        }        System.out.println("ChatterClient starting");    }    public void run() {        try {            for (int i = 0; i < 25; i++) {                String outMessage = "Client #" + id + ",message #" + i;                s.send(Dgram.toDatagram(outMessage, hostAddress,                        ChatterServer.INPORT));                s.receive(dp);                String rcvd = "Client #" + id + ",rcvd from " + dp.getAddress()                        + ", " + dp.getPort() + ":" + Dgram.toString(dp);                System.out.println(rcvd);            }        } catch (IOException e) {            e.printStackTrace();            System.exit(1);        }    }    public static void main(String[] args) {        for (int i = 0; i < 10; i++) {            new ChatterClient(i).start();        }    }}