How to set the jProgressBar working according to the time taken for a task in java

Question

I m developing application that encrypt decrypt files, i want to use a jProgressBar according to the real time taken to the process.

Answer 1

To make the jProgressBar work according to the time taken for a task, you should use SwingWorker to perform the task in a separate thread.

How SwingWorker works?

SwingWorker is designed for situations where you need to have a long running task run in a background thread and provide updates to the UI either when done, or while processing. Subclasses of SwingWorker must implement the doInBackground() method to perform the background computation.

Workflow

There are three threads involved in the life cycle of a SwingWorker :

Current thread: The execute() method is called on this thread. It schedules SwingWorker for the execution on a worker thread and returns immediately. One can wait for the SwingWorker to complete using the get methods.

Worker thread: The doInBackground() method is called on this thread. This is where all background activities should happen. To notify PropertyChangeListeners about bound properties changes use the firePropertyChange and getPropertyChangeSupport() methods. By default there are two bound properties available: state and progress.

Event Dispatch Thread: All Swing related activities occur on this thread. SwingWorker invokes the process and done() methods and notifies any PropertyChangeListeners on this thread.

Often, the Current thread is the Event Dispatch Thread.

So, to develop an application that encrypts and decrypts files, you can use a SwingWorker to perform the encryption/decryption and jProgressBar according to the real time taken to the process.

Sample output:

Code:

public class Test extends JPanel implements ActionListener,
        PropertyChangeListener {

    private JProgressBar progressBar;
    private JButton startButton;
    private JTextArea encryptedOutput;
    private JTextArea decryptedOutput;
    private Task task;

    Key aesKey;
    Cipher cipher;
    String key = "Code1234Code1234"; // 128 bit key

    class Task extends SwingWorker<Void, Void> {
        @Override
        public Void doInBackground() {
            int progress = 0;
            // Initialize progress property.
            setProgress(0);

            try {

                JFileChooser fileopen = new JFileChooser();
                FileFilter filter = new FileNameExtensionFilter("txt files",
                        "txt");
                fileopen.addChoosableFileFilter(filter);

                File file = null;
                String fileName = "";
                int ret = fileopen.showDialog(null, "Open file");

                if (ret == JFileChooser.APPROVE_OPTION) {
                    file = fileopen.getSelectedFile();
                    fileName = file.getName();

                    encryptedOutput.setText(String.format(
                            "Encrypted Output :  %s\t\n\n", fileName));
                    decryptedOutput.setText(String.format(
                            "Decrypted Output  : %s\t\n\n", fileName));
                    BufferedReader in = new BufferedReader(new FileReader(file));
                    String line = in.readLine();
                    long readLength = 0;
                    long totalLength = file.length();
                    double lengthPerPercent = 100.0 / totalLength;
                    // added dummy delay because encryption takes very less time
                    // in MVCE
                    Thread.sleep(1000);
                    while (line != null) {
                        try {

                            Thread.sleep(100);
                            // encrypt the text
                            cipher.init(Cipher.ENCRYPT_MODE, aesKey);
                            byte[] encrypted = cipher.doFinal(line.getBytes());

                            encryptedOutput.append(String.format("%s\n",
                                    new String(encrypted)));

                            // decrypt the text
                            cipher.init(Cipher.DECRYPT_MODE, aesKey);
                            String decrypted = new String(
                                    cipher.doFinal(encrypted));
                            decryptedOutput.append(String.format("%s\n",
                                    decrypted));

                            // calculate progress.
                            readLength += line.length();
                            progress = (int) (lengthPerPercent * readLength);
                            setProgress(Math.min(progress, 100));
                            line = in.readLine();
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
            }

            return null;
        }

        /*
         * Executed in event dispatching thread
         */
        @Override
        public void done() {
            setProgress(100);
            Toolkit.getDefaultToolkit().beep();
            startButton.setEnabled(true);

            // turn off the wait cursor
            setCursor(null);
        }
    }

    public Test() {

        super(new BorderLayout());

        // Create key and cipher
        aesKey = new SecretKeySpec(key.getBytes(), "AES");
        try {
            cipher = Cipher.getInstance("AES");
        } catch (Exception e) {
            e.printStackTrace();
        }

        progressBar = new JProgressBar(0, 100);
        progressBar.setValue(0);
        progressBar.setStringPainted(true);

        encryptedOutput = new JTextArea(20, 50);
        encryptedOutput.setMargin(new Insets(5, 5, 5, 5));
        encryptedOutput.setEditable(false);
        encryptedOutput.setLineWrap(true);

        decryptedOutput = new JTextArea(20, 50);
        decryptedOutput.setMargin(new Insets(5, 5, 5, 5));
        decryptedOutput.setEditable(false);
        decryptedOutput.setLineWrap(true);

        startButton = new JButton("Start Encoding");
        startButton.setActionCommand("start");
        startButton.addActionListener(this);

        JPanel panel = new JPanel();
        add(panel, BorderLayout.PAGE_START);
        panel.add(progressBar, BorderLayout.LINE_START);
        add(new JScrollPane(encryptedOutput), BorderLayout.LINE_START);
        add(new JScrollPane(decryptedOutput), BorderLayout.LINE_END);
        panel.add(startButton, BorderLayout.PAGE_END);
        setBorder(BorderFactory.createEmptyBorder(50, 50, 50, 50));

    }

    public void actionPerformed(ActionEvent evt) {
        startButton.setEnabled(false);
        setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));
        task = new Task();
        task.addPropertyChangeListener(this);
        task.execute();
    }

    /**
     * Invoked when task's progress property changes.
     */
    public void propertyChange(PropertyChangeEvent evt) {
        if (evt.getPropertyName().equals("progress")) {
            int progress = (Integer) evt.getNewValue();
            progressBar.setValue(progress);
            encryptedOutput.append("\n\n");
        }
    }

    private static void createAndShowGUI() {
        JFrame frame = new JFrame("Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JComponent newContentPane = new Test();
        newContentPane.setOpaque(true);
        frame.setContentPane(newContentPane);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}

Related Documentation:

• Worker Threads and SwingWorker