如何知道远程服务器是否与遥控器Java代码断开连接

Question

我有此代码，如果从服务器窗口断开连接，我需要在标签中显示"断开连接"。我的问题是我不知道如何检测是否断开连接。我想检测连接状态，即使没有连接或另一端没有扳机。

//  Copyright 2012
//  Android Remote Desktop Server Ver. 1.0

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.net.*;
import java.util.Random;
public class ServerWindow implements ActionListener{
    private RemoteDataServer server;

    private Thread sThread; //server thread
    private static final int WINDOW_HEIGHT = 200;
    private static final int WINDOW_WIDTH = 350;
    private String ipAddress;
    private JFrame window = new JFrame("Remote Control for Android");
    private JLabel addressLabel = new JLabel("");
    private JLabel portLabel = new JLabel("Android Remote Control Port: ");
    private JTextArea[] buffers = new JTextArea[3];
    private JTextField portTxt = new JTextField(5);
    private JLabel serverMessages = new JLabel("Not Connected");
    private JButton connectButton = new JButton("Start Server");
    private JButton disconnectButton = new JButton("Stop Server");
    public boolean connected = false;
    public ServerWindow(){
        server = new RemoteDataServer();
        window.setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        connectButton.addActionListener(this);
        disconnectButton.addActionListener(this);
        Container c = window.getContentPane();
        c.setLayout(new FlowLayout());
        try{
            InetAddress ip = InetAddress.getLocalHost();
            ipAddress = ip.getHostAddress();
            addressLabel.setText("Android Remote Control Server IP Address: "+ipAddress);
        }
        catch(Exception e){addressLabel.setText("IP Address Could Not be Resolved");}
        int x;
        for(x = 0; x < 3; x++){
            buffers[x] = new JTextArea("", 1, 30);
            buffers[x].setEditable(false);
            buffers[x].setBackground(window.getBackground());
        }
        portTxt.setEditable(false);
        Random portRandom = new Random();
        for (int i = 0; i < 10; i++) {
          int port = portRandom.nextInt(4998) + 1;
          int portNum = 5000+port;
          String portString = Integer.toString(portNum);
          portTxt.setText(portString);
          }
        c.add(addressLabel);
        c.add(buffers[0]);
        c.add(portLabel);
        //portTxt.setText("5444");
        c.add(portTxt);
        c.add(buffers[1]);
        c.add(connectButton);
        c.add(disconnectButton);
        c.add(buffers[2]);
        c.add(serverMessages);
        window.setLocationRelativeTo(null);
        window.setVisible(true);
        window.setResizable(false);
    }
    public void actionPerformed(ActionEvent e){
        Object src = e.getSource();
        if(src instanceof JButton){
            if((JButton)src == connectButton){
                int port = Integer.parseInt(portTxt.getText());
                runServer(port);
            }
            else if((JButton)src == disconnectButton){
                closeServer();
            }
        }
    }
    public void runServer(int port){
        if(port <= 9999){
            server.setPort(port);
            sThread = new Thread(server);
            sThread.start();
        }
        else{
            serverMessages.setText("The port Number must be less than 10000");
        }
    }
    public void closeServer(){
        serverMessages.setText("Disconnected");
        server.shutdown();
        connectButton.setEnabled(true);
    }
    public static void main(String[] args){
        new ServerWindow();
    }
    public class RemoteDataServer implements Runnable{
        int PORT;
        private DatagramSocket server;
        private byte[] buf;
        private DatagramPacket dgp;
        private String message;
        private AutoBot bot;

        public RemoteDataServer(int port){
            PORT = port;
            buf = new byte[1000];
            dgp = new DatagramPacket(buf, buf.length);
            bot = new AutoBot();
            serverMessages.setText("Not Connected");
        }
        public RemoteDataServer(){
            buf = new byte[1000];
            dgp = new DatagramPacket(buf, buf.length);
            bot = new AutoBot();
            serverMessages.setText("Not Connected");
        }
        public String getIpAddress(){
            String returnStr;
            try{
                    InetAddress ip = InetAddress.getLocalHost();
                    returnStr = ip.getCanonicalHostName();
            }
            catch(Exception e){ returnStr = new String("Could Not be Resolve Ip Address");}
            return returnStr;
        }
        public void setPort(int port){
            PORT = port;
        }
        public void shutdown(){
            try{server.close();
                serverMessages.setText("Disconnected");}
            catch(Exception e){}
        }
        public void run(){
            //boolean connected = false;
            try {InetAddress ip = InetAddress.getLocalHost(); 
                serverMessages.setText("Waiting for connection on " + ip.getCanonicalHostName());
                server = new DatagramSocket(PORT, ip);
                connected = true;
                connectButton.setEnabled(false);
            }
            catch(BindException e){ serverMessages.setText("Port "+PORT+" is already in use. Use a different Port"); }
            catch(Exception e){serverMessages.setText("Unable to connect");}
            while(connected){
                //Runtime.getRuntime().exit(0);
                // get message from sender
                try{ server.receive(dgp);
                    // translate and use the message to automate the desktop
                    message = new String(dgp.getData(), 0, dgp.getLength());
                    if (message.equals("Connectivity")){
                        //send response to confirm connectivity
                        serverMessages.setText("Trying to Connect");
                        server.send(dgp); //echo the message back
                    }else if(message.equals("Connected")){
                        server.send(dgp); //echo the message back
                    }else if(message.equals("Close")){
                        serverMessages.setText("Controller has Disconnected. Trying to reconnect."); //echo the message back
                    }else{
                        serverMessages.setText("Android Phone Connected to ARD Server");
                        bot.handleMessage(message);
                        server.receive(dgp);
                    }
                }catch(Exception e){
                    serverMessages.setText("Disconnected");
                    connected = false;}
            }
        }
    }
    }

Answer 1

由于您使用UDP，因此在两个对等方之间没有"真实"连接，因此您可能需要从客户端执行某种定期的保留请求。如果没有收到任何响应，则保持活力，这意味着您已断开连接。