import java.net.*;

public class UDPServer {
    private static final int PORT = 5000;
    private DatagramSocket dataSocket;
    private DatagramPacket dataPacket;
    private byte receiveByte[];
    private String receiveStr;

    public UDPServer() {
        Init();
    }

    public void Init() {
        try {
            dataSocket = new DatagramSocket(PORT);
            receiveByte = new byte[1024];
            dataPacket = new DatagramPacket(receiveByte, receiveByte.length);
            receiveStr = "";
            int i = 0;
            while (i == 0)// 无数据，则循环

            {
                dataSocket.receive(dataPacket);
                i = dataPacket.getLength();
                // 接收数据

                if (i > 0) {
                    // 指定接收到数据的长度,可使接收数据正常显示,开始时很容易忽略这一点

                    receiveStr = new String(receiveByte, 0, dataPacket.getLength());
                    System.out.println(receiveStr);
                    i = 0;// 循环接收

                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String args[]) {
        new UDPServer();
    }
}

import java.io.*;
import java.net.*;

public class UDPClient {
    private static final int PORT = 5000;
    private DatagramSocket dataSocket;
    private DatagramPacket dataPacket;
    private byte sendDataByte[];
    private String sendStr;

    public UDPClient() {
        Init();
    }

    public void Init() {
        try {
            // 指定端口号，避免与其他应用程序发生冲突

            dataSocket = new DatagramSocket(PORT);
            sendDataByte = new byte[1024];
            sendStr = "UDP方式发送数据";
            sendDataByte = sendStr.getBytes();
            dataPacket = new DatagramPacket(sendDataByte, sendDataByte.length,
                    InetAddress.getByName("localhost"), PORT);
            dataSocket.send(dataPacket);
        } catch (SocketException se) {
            se.printStackTrace();
        } catch (IOException ie) {
            ie.printStackTrace();
        }
    }

    public static void main(String args[]) {
        new UDPClient();
    }
}