import java.awt.*;
import java.awt.event.*;
import java.net.*;
import javax.swing.*;

public class UDPServerDemo extends JFrame{	
	int port=2345;	//端口號
	
	public UDPServerDemo(){
		try{
			byte[] buffer=new byte[256]; //緩沖區數組
			DatagramSocket socket=new DatagramSocket(port);	 //實例化數據報Socket
			DatagramPacket packet; 
			System.out.println("Server start..."); //輸出運行信息
			
			while (true){
				packet=new DatagramPacket(buffer,buffer.length); //實例化數據報
				socket.receive(packet);	 //接受請求							
				InetAddress target=packet.getAddress(); 
				System.out.println("Received from"+target); //輸出請求地址
				int port=packet.getPort(); //得到接收端口
				byte[] message="This is server,Who are you?".getBytes(); //服務器返回信息
				packet=new DatagramPacket(message,message.length,target,port); //實例化數據報
				socket.send(packet); //發送數據報
			}			
		}
		catch (Exception ex){
			ex.printStackTrace(); //輸出出錯信息
		}
	}
	
	public static void main(String[] args){
		new UDPServerDemo();
	}
}