基础知识

客户端

import java.io.*;
import java.net.*;
public class UDPClientTest {
    public static void main(String args[]) {
          DatagramSocket sendSocket = null;
          try {
                sendSocket = new DatagramSocket(3456);
                String string = "0000009390832";
                byte[] databyte = new byte[100];
                databyte = string.getBytes();
                DatagramPacket sendPacket = new DatagramPacket(databyte, string.length(),
                        InetAddress.getLocalHost(), 10000);
                sendSocket.send(sendPacket);
                System.out.println("客户端开始传送数据！");
          } catch (SocketException e) {
                System.out.println("不能打开数据报Socket，或数据报Socket无法与指定端口连接!");
          } catch (IOException ioe) {
                System.out.println(ioe.toString());
          } finally {
                sendSocket.close();
          }
    }
}

服务器（receive会阻塞，采用线程）

import java.io.*;
import java.net.*;
public class UDPServerTest {
   static public void main(String args[]) {
       try {
           DatagramSocket receiveSocket = new DatagramSocket(10000);
           byte buf[] = new byte[1000];
           DatagramPacket receivePacket = new DatagramPacket(buf, buf.length);
           System.out.println("开始接受数据：");
           //启动接收端线程
           new Thread(new recthread(receiveSocket,receivePacket)).start();
       }
       catch (SocketException e) {
           e.printStackTrace();
           System.exit(1);
       }
   }
}
//因为要一直接收数据，所以接收receive会阻塞，所以创建一个线程，防止阻塞
class recthread extends Thread{
    DatagramSocket ds=null;
    DatagramPacket dp;
    public recthread(DatagramSocket ds,DatagramPacket dp){
        this.ds=ds;
        this.dp=dp;
    }
    public void run( ){
        while (true) {
            try {
                ds.receive(dp);
            } catch (IOException e) {
                e.printStackTrace();
            }
            String name = dp.getAddress().toString();
            System.out.println("\n来自主机：" + name + "\n端口：" + dp.getPort());
            String s = new String(dp.getData(), 0, dp.getLength());
            System.out.println("接受到的数据是: " + s);
        }
    }
}