public class UDPRunnable extends Thread{

DatagramPacket packet;;

//初始化DatagramPacket, DatagramSocket

public UDPRunnable(DatagramPacket packet){

this.packet=packet;

}

public void run() {

byte[] data=packet.getData();//!!!这里应该使用packet的getData方法来创建data字节，不然data字节中为空值

String info=new String(data,0,packet.getLength());//

System.out.println("我是服务器，客户端说："+info);

/*

* 服务器向客户端发送响应信息

*/

//需要知道客户端的address，port，并且创建需要发送的消息

InetAddress address=packet.getAddress();

int port=packet.getPort();

byte[] data2="客户端登陆成功，欢迎使用服务器".getBytes();

//创建DatagramPacket

DatagramPacket packet2=new DatagramPacket(data2,data2.length,address,port);

try {

DatagramSocket socket=new DatagramSocket();

socket.send(packet2);

} catch (SocketException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

}

public class UDPClient {

public static void main(String[] args) throws IOException {

/*

* 向服务器端发送消息

*/

//1.需要获取服务器端的地址，端口号

InetAddress address=InetAddress.getByName("localhost");

int port=6605;

byte[] message="用户名：admin 密码:123".getBytes();

//创建数据报

DatagramPacket packet=new DatagramPacket(message,message.length,address,port);

//创建DatagramSocket

DatagramSocket socket=new DatagramSocket();

socket.send(packet);

/*

* 接收服务器端发送的响应消息

*/

//创建DatagramPacket

byte[] data=new byte[10*1024];

DatagramPacket packet2=new DatagramPacket(data,data.length);

socket.receive(packet2);

String reply=new String(data,0,packet.getLength());

System.out.println("我是客户端，服务器说："+reply);

}

}

客户端输出结果：  客户端启动成功，欢迎使