UDP消息发送

发送端：

package inet;



import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

//不需要连接服务器
public class UDPDemo1 {
    public static void main(String[] args) throws Exception {
        //建立一个socket
        DatagramSocket dgs=new DatagramSocket();

        //建立一个包
        String msg="hello,server!";

        //发送给谁
        InetAddress ad = InetAddress.getByName("localhost");
        int port=9090;
        //数据，数据的长度起始，连接对象地址，端口
        DatagramPacket datagramPacket = new DatagramPacket(msg.getBytes(),0,msg.getBytes().length,ad,port);
        //发送包
        dgs.send(datagramPacket);

        //关闭流
        dgs.close();

    }

}

接收端：

package inet;



import java.net.DatagramPacket;
import java.net.DatagramSocket;




public class UDPDemo2 {
    public static void main(String[] args) throws Exception {

        //开放端口
        DatagramSocket socket=new DatagramSocket(9090);
        //接收数据包
        byte[] buffer = new byte[1024];
        DatagramPacket packet = new DatagramPacket(buffer, 0, buffer.length);
        socket.receive(packet);//阻塞接收，一直在监听等待

        System.out.println(packet.getAddress().getHostAddress());

        System.out.println(new String(packet.getData(),0,packet.getLength()));


        //关闭连接
        socket.close();


    }
}