I can't stop java SwingWorker process

Question

I was running a tcp server in java which is done using SwingWorker class. First time it will start successful but when i stop and start the process it won't work. i couldn't find what is the bug please help me to fix this

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.ServerSocket;
import java.net.Socket;

public class SwingWorkerDemo extends JFrame {
     /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private static ServerSocket serverSocket;
        private static Socket clientSocket;
        private static InputStreamReader inputStreamReader;
        private static BufferedReader bufferedReader;
        private static String message;

    public SwingWorkerDemo() {
        initialize();
    }

    private void initialize() {
        this.setLayout(new FlowLayout());
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        final JButton startButton = new JButton("Start");
        final JButton stopButton = new JButton("Stop");
        final LongRunProcess process = new LongRunProcess();



        startButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent event) {
                try {
                    process.execute();
                } catch (Exception e) {
                    e.printStackTrace();
                }
                startButton.setEnabled(false);
                stopButton.setEnabled(true);
            }
        });

        stopButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
               // JOptionPane.showMessageDialog(null, "Hello There");

process.cancel(true);
startButton.setEnabled(true);
stopButton.setEnabled(false);
            }
        });


        this.getContentPane().add(startButton);
        this.getContentPane().add(stopButton);

        this.pack();
        this.setSize(new Dimension(300, 80));
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new SwingWorkerDemo().setVisible(true);
            }
        });
    }

    class LongRunProcess extends SwingWorker {
        /**
         * @throws Exception
         */
        protected Object doInBackground() throws Exception {
            try {
                serverSocket = new ServerSocket(4545);  //Server socket

            } catch (IOException e) {
                System.out.println("Could not listen on port: 4545");
            }

            System.out.println("Server started. Listening to the port 4545");

            while (true) {
                try {

                    clientSocket = serverSocket.accept();   //accept the client connection
                    inputStreamReader = new InputStreamReader(clientSocket.getInputStream());
                    bufferedReader = new BufferedReader(inputStreamReader); //get the client message
                    message = bufferedReader.readLine();
     if(message.equals("shutdown")){

    Runtime runtime = Runtime.getRuntime();
    Process proc = runtime.exec("shutdown -s -t 00");
    System.exit(0);

     }
     else if(message.equals("restart")){
    Runtime runtime1 = Runtime.getRuntime();
    Process proc2 = runtime1.exec("shutdown -r -t 00");
    System.exit(0);


     }

                    System.out.println(message);
                    inputStreamReader.close();
                    clientSocket.close();

                } catch (IOException ex) {
                    System.out.println("Problem in message reading");
                }
            }

    }
    }
}

Answer 1

You can use this. In this i have made some changes also

public class Test extends JFrame {
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private static ServerSocket serverSocket;
    private static Socket clientSocket;
    private static InputStreamReader inputStreamReader;
    private static BufferedReader bufferedReader;
    private static String message;

    public Test() {
        initialize();
    }

    LongRunProcess process;

    private void initialize() {
        this.setLayout(new FlowLayout());
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        final JButton startButton = new JButton("Start");
        final JButton stopButton = new JButton("Stop");

        startButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent event) {
                try {
                    process = new LongRunProcess();
                    process.start();
                } catch (Exception e) {
                    e.printStackTrace();
                }
                startButton.setEnabled(false);
                stopButton.setEnabled(true);
            }
        });

        stopButton.addActionListener(new ActionListener() {
            @SuppressWarnings("deprecation")
            public void actionPerformed(ActionEvent e) {
                // JOptionPane.showMessageDialog(null, "Hello There");

                process.closeServer();

                startButton.setEnabled(true);
                stopButton.setEnabled(false);
                process.stop();
            }
        });

        this.getContentPane().add(startButton);
        this.getContentPane().add(stopButton);

        this.pack();
        this.setSize(new Dimension(300, 80));
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new Test().setVisible(true);
            }
        });
    }

    class LongRunProcess extends Thread {
        /**
         * @throws Exception
         */
        public void closeServer() {
            try {
                serverSocket.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("Closed Now");
        }

        public void run() {
            try {
                serverSocket = new ServerSocket(4545); // Server socket

            } catch (IOException e) {
                System.out.println("Could not listen on port: 4545");
            }

            System.out.println("Server started. Listening to the port 4545");

            while (!(serverSocket.isClosed())) {
                try {

                    clientSocket = serverSocket.accept(); // accept the client
                                                            // connection
                    inputStreamReader = new InputStreamReader(
                            clientSocket.getInputStream());
                    bufferedReader = new BufferedReader(inputStreamReader); // get
                                                                            // the
                                                                            // client
                                                                            // message
                    message = bufferedReader.readLine();
                    if (message.equals("shutdown")) {

                        Runtime runtime = Runtime.getRuntime();
                        Process proc = runtime.exec("shutdown -s -t 00");
                        System.exit(0);

                    } else if (message.equals("restart")) {
                        Runtime runtime1 = Runtime.getRuntime();
                        Process proc2 = runtime1.exec("shutdown -r -t 00");
                        System.exit(0);

                    }

                    System.out.println(message);
                    inputStreamReader.close();
                    clientSocket.close();

                } catch (IOException ex) {
                    System.out.println("Problem in message reading");
                }
            }
        }
    }
}

Answer 2

As per the Javadocs of SwingWorker#execute()

Note: SwingWorker is only designed to be executed once. Executing a SwingWorker more than once will not result in invoking the doInBackground method twice.

Hence the behavior you are seeing. So in order to achieve what you are looking. you need to create new Instance of LongRunProcess every time you push start button. Something like this.

declare at class level

LongRunProcess process = null;

modify action listener

 startButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent event) {
            try {
                process = new LongRunProcess();
                process.execute();
            } catch (Exception e) {
                e.printStackTrace();
            }
            startButton.setEnabled(false);
            stopButton.setEnabled(true);
        }
    });

Hope this helps.