Network Transport Protocol - I wrote a simple chat software in Java using UDP, but I always cannot receive messages?

Question

Written a simple chat software in Java using UDP, but I can't receive any messages. Please let me know what's wrong with the code.

package com.window;

import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.logging.Logger;

/**
 * Created by young on 2017/4/19.
 */
public class MainWindow {

    private JLabel lb_addIp;
    private JButton btn_add;
    private JPanel jp_qq;
    private JLabel lb_selectIP;
    private JComboBox<String> cb_selectIP;
    private JTextField tf_addip;
    private JTextArea ta_charHistory;
    private JTextField tf_input;
    private JButton btn_submit;
    private JLabel lb_charHistory;
    private JLabel lb_message;
    private JTextPane tp;

    private String ip;
    private String sendMessage;

    private int sendport = 10023;

    private int receviceport = 10024;

    private DefaultListModel<String> listModel = new DefaultListModel<String>();
    public String name;
    private List<String> messageList = new ArrayList<>();

    public MainWindow() {

        btn_add.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                ip = tf_addip.getText();
                Object[] com = new Object[]{ip};
                cb_selectIP.addItem(ip);
            }
        });
        btn_submit.addMouseListener(new MouseAdapter() {
            Logger logger = Logger.getLogger("submit");

            @Override
            public void mouseClicked(MouseEvent e) {
                if (ip == null) {
                    lb_message.setForeground(Color.red);
                    lb_message.setText("请输入IP。");
                    return;
                }
                try {
                    InetAddress inetAddress = InetAddress.getByName(ip);
                    if (!inetAddress.isReachable(2000)) {
                        lb_message.setForeground(Color.red);
                        lb_message.setText("无法链接该地址！");
                        return;
                    }
                } catch (IOException e1) {
                    e1.printStackTrace();
                }

                sendMessage = tf_input.getText();

                logger.info("sendMessage" + sendMessage);


                new Thread(() -> {
                    send(sendMessage);
                    lb_message.setForeground(Color.green);
                    lb_message.setText("发送成功。");
                }).start();
                new Thread(() -> {
                    receive();
                }).start();
            }
        });

    }

    public void receive() {
        DatagramSocket datagramSocket = null;
        try {
            datagramSocket = new DatagramSocket(sendport, InetAddress.getByName(ip));
            byte[] buf = new byte[1024];
            DatagramPacket datagramPacket = new DatagramPacket(buf, buf.length);
            datagramSocket.receive(datagramPacket);
            String id = datagramPacket.getAddress().getHostAddress();
            int port = datagramPacket.getPort();
            byte[] date = datagramPacket.getData();
            System.out.println(Arrays.toString(date));
            String mes = ip + ":" + new String(date) + "\n";
            //System.out.println("ip=" + id + "port=" + port);
            tp.setText(tp.getText() + mes);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            assert datagramSocket != null;
            datagramSocket.close();
        }
    }

    public void initWindow() {
        JFrame frame = new JFrame("QQ");
        frame.setContentPane(new MainWindow().jp_qq);
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.pack();
        frame.setVisible(true);
        tp.setEditable(false);
    }

    public void send(String message) {
        DatagramSocket datagramSocket = null;
        try {
            datagramSocket = new DatagramSocket(receviceport);
            byte[] buf = message.getBytes();
            DatagramPacket packet = new DatagramPacket(buf, buf.length, InetAddress.getByName(ip), sendport);
            datagramSocket.send(packet);
            tp.setText(tp.getText() + name + message + "\n");
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            datagramSocket.close();
        }
    }

}

There is a lot of code, so I put it on github
github address

Answer 1

You execute sending and receiving in two threads respectively. This raises a problem. It is possible to perform reception first and then send, or it is possible to perform reception during the sending process. The phenomenon that occurs is that sometimes the data can be received, but sometimes not.