Question

I have this code. I want to exit my Java Application if it detects that the computer is shutting down. I have this problem, If shutdown is clicked on windows my java application disconnects from android app connection. I want to display that the java application has been disconnected or it will exit.

//  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;




    //@SuppressWarnings("deprecation")
    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);
                    }
                }catch(Exception e){
                    serverMessages.setText("Disconnected");
                    connected = false;}
            }

        }
    }
}

Answer 1

Assuming that the question you meant to ask is “how to detect when Windows is being shut down”, here is how you do it:

You need a so-called “System Shutdown Hook”, which is essentially a Thread who’s run() method is executed whenever the Java virtual machine shuts down. The happens either when your program terminates or because of a system-wide event, such as a user log-off or a shut-down.

All you need to do is put this piece of code somewhere in the startup process of your program:

Runtime.getRuntime().addShutdownHook(
    new Thread(new Runnable() {
        @Override
        public void run() {
            // this is executed on shut-down. put whatever.
        }
    }));

I hope this answers your question.