Brothers of the previous one
Previous address: https://www.jianshu.com/p/457b24e5e0a5

UDP based

UDP protocol takes data packets as the carrier of data transmission, that is, when data transmission, we need to package data into datagrams, in which the host address and port number are specified, and then the datagrams are sent out, using two key categories:

• Datagram packet
• Datagram socket class for end-to-end communication

The server

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        new Thread(){
            @Override
            public void run() {
                try {
                    //Step 1 create datagram socket on the server side and specify the port

                    DatagramSocket socket = new DatagramSocket(8899);
                    //Step 2 create a datagram to receive the data sent by the client
                    byte[] data =new byte[1024];//Create a byte array to specify the received packet size
                    DatagramPacket packet=new DatagramPacket(data, data.length);
                    //Step ③ receive the data sent by the client
                    System.out.println("server loaded success,waiting...");
                    socket.receive(packet);//This method will block until a datagram is received
                    //Step 4 read the data
                    String info=new String(data, 0, packet.getLength());
                    //For the sake of simplicity, the logic of verification is no longer written here

                    //Step ⑤ define the address, port number and data of the client
                    InetAddress address=packet.getAddress();
                    int port=packet.getPort();
                    byte[] data2="Welcome!!!".getBytes();
                    //Step 6 create a datagram containing the data information of the response
                    DatagramPacket packet2=new DatagramPacket(data2, data2.length, address, port);
                    //Step ⑦ respond to the client
                    socket.send(packet2);
                    //Step ⑧ close resources
                    socket.close();
                } catch (SocketException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }.start();


    }
}

client

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        new Thread(){
            @Override
            public void run() {
                //Step ① define the address, port number and data of the server
                InetAddress address= null;
                try {
                    address = InetAddress.getByName("localhost");
                } catch (UnknownHostException e) {
                    e.printStackTrace();
                }
                int port=8899;
                byte[] data="admin:123".getBytes();
                //Step 2 create a datagram, including the data information sent
                DatagramPacket packet=new DatagramPacket(data, data.length, address, port);

                try {
                    //Step 3 create DatagramSocket object
                    DatagramSocket socket = new DatagramSocket();
                    //Step 4 send datagram to server
                    socket.send(packet);
                    //Step ⑤ create a datagram to receive the data from the server
                    byte[] data2=new byte[1024];
                    DatagramPacket packet2=new DatagramPacket(data2, data2.length);
                    //Step 6 receive the data from the server
                    socket.receive(packet2);
                    //Step ⑦ read data
                    String reply=new String(data2, 0, packet2.getLength());
                    System.out.println("server reply : "+reply);
                    //Step ⑧ close resources
                    socket.close();
                } catch (SocketException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }.start();


    }
}