UDP協議：
UDP協議傳輸數據是不可靠的，在java中，java.util.DatagramSocket負責接收和發送UDP數據報，java.util.DatagramPacket表示UDP數據表。每個
DatagramSocket與一個本底地址綁定，每個DatagramSocket可以把UDP數據報發送給任意一個遠程DatagramSocket，也可以接收來自任意一個遠程的
DatagramSocket的UDP數據報。在UDP數據報中包含了目的地址信息，DatagramSocket根據該信息把數據報發送到目的地

UDP服務端

public class EchoServer{
    
    
 
private int port = 8089;
    private DatagramSocket socket;
    
    public EchoServer()throws IOException{
        socket = new DatagramSocket(port);
        System.out.println("服務端啟動");
    }
    
    public String ehco(String msg){
        return "ehco:"+msg;
    }
    
    public void
 
 service(){
        while(true){
            try {
                //創建一個數據報對象
                DatagramPacket packet = new DatagramPacket(new byte[512], 512);
                socket.receive(packet);//接收來自任意一個EhcoClient的數據報
                String msg = new String(packet.getData(), 0, packet.getLength());
                System.out.println(packet.getAddress()
 
+":"+packet.getPort()+">"+msg);
                packet.setData(ehco(msg).getBytes());//給EchoClient發送數據報
                socket.send(packet);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
    
    public static void main(String[] args) throws IOException {
        new EchoServer().service();
    }
    
}

UDP客戶端

public class EchoClient {

    private String remoteHost = "localhost";
    private int remotePort = 8089;
    private DatagramSocket socket;
    
    public EchoClient() throws SocketException{
        socket = new DatagramSocket();//與本地任意的端口綁定
    }
    
    public void talk() throws IOException{
        try{
            //獲取服務端ip地址
            InetAddress remoteIP = InetAddress.getByName(remoteHost);
            
            BufferedReader localReader = new BufferedReader(new InputStreamReader(System.in));
            String msg = null;
            while((msg = localReader.readLine()) != null){
                byte[] outputData = msg.getBytes();
                DatagramPacket outputPacket = new DatagramPacket(
                        outputData, outputData.length,remoteIP,remotePort);
                
                socket.send(outputPacket);//發送數據報
                
                DatagramPacket inputPacket = new DatagramPacket(new byte[512], 512);
                socket.receive(inputPacket);//接收EchoServer的數據報
                System.out.println(new String(inputPacket.getData(),0,inputPacket.getLength()));
                if(msg.equals("bye")){
                    break;
                }
            }
        }catch (Exception e) {
            e.printStackTrace();
        }finally{
            socket.close();
        }
    }
    
    public static void main(String[] args) throws SocketException, IOException {
        new EchoClient().talk();
    }
    
}

Udp簡單的服務器與客戶端07