Modal dialog not working

Question

When opening a second dialog as a 'loading dialog' to prevent user action while loading a large file, I want the dialog to restrict any user action (click and such) while the dialog is up (and the large file is loading). The dialog works as a 'Non-Modal dialog' which you can click back to the main window and click on stuff, but when using a 'Modal dialog' instead it freezes the program's processes once it is displayed.

How can I get the modal dialog to display correctly?

Code:

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import javax.xml.parsers.*;
import javax.xml.xpath.*;
import java.util.logging.*;
import org.w3c.dom.*;
import java.io.File;
import java.lang.reflect.InvocationTargetException;
import java.net.URL;
import javax.swing.filechooser.FileNameExtensionFilter;

public class Loader implements Runnable  {

    final JFileChooser jfc = new JFileChooser();
    static JFrame frame = new JFrame();
    Frame parentUI = new  Frame();
    JDialog dialog = new JDialog();
    JLabel lbl_filename = new JLabel();
    JLabel lbl_path = new JLabel();

    static Loader load = new Loader(null);


    public static void main(String[] args) throws InterruptedException, InvocationTargetException {
        load.run();
        frame.setVisible(true);
    } 

    public Loader(Frame parent) {
        init();
        parentUI = parent;
    }

    @Override
    public void run() {
        createDialog(parentUI);
    }  

    public final void init() {
        JButton btn = new JButton("Open");

        frame.setTitle("Loader Test");
        frame.setSize(500, 200);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);
        frame.setLayout(new FlowLayout());

        btn.addActionListener(new Action1());

        frame.add(btn);
        frame.add(lbl_filename);
        frame.add(lbl_path);
    }

    class Action1 implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent e) {

            openFile();
        }
    }

    private void createDialog(final Frame parent) {

        dialog.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
        dialog.setModal(true);
        dialog.setTitle("Loader");

        URL url = this.getClass().getResource("/resource/loader.gif");
        Icon icon = new ImageIcon(url);
        JLabel label = new JLabel(icon);
        dialog.add(label);

        dialog.pack();
        dialog.setLocationRelativeTo(parent);
    }


    public void Show(Boolean visible) {
        this.run();
        dialog.setVisible(visible);
    }

    public void Close() {
        dialog.setVisible(false);
    }

    private void setJFCFilter(String file, String ext) {
        FileNameExtensionFilter filter = new FileNameExtensionFilter(file, ext);
        jfc.setFileFilter(filter);
    }

    private void openFile() {
        File default_dir = new File(".");
        jfc.setCurrentDirectory(default_dir);
        setJFCFilter("Scalable Vector Graphics", "svg");

        int returnVal = jfc.showOpenDialog(parentUI);

        if (returnVal == JFileChooser.APPROVE_OPTION) {
            final String path = jfc.getSelectedFile().getAbsolutePath();
            String fileName = jfc.getSelectedFile().getName();

            lbl_filename.setText(fileName);
            lbl_path.setText(path);

            System.out.println("Loading file...");

            load.Show(true);

            new SwingWorker<Void, Void>() {
                @Override
                protected Void doInBackground() throws Exception {
                    createDoc(path);
                    return null;
                };

                @Override
                protected void done() {
                    load.Close();
                };
            }.execute();

            System.out.println("Closing file...");
        }
    }

    private void createDoc(String file) {
        try {
            NodeList svgIDPaths;

            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
            DocumentBuilder builder = factory.newDocumentBuilder();
            Document doc = builder.parse(file);

            String xpathIDExp = "//g/@id";

            XPathFactory xpf = XPathFactory.newInstance();
            XPath xpath = xpf.newXPath();
            XPathExpression expression = xpath.compile(xpathIDExp);

            svgIDPaths = (NodeList)expression.evaluate(doc, XPathConstants.NODESET); // Java OutOfMemory

        } catch (Exception ex) {
            Logger.getLogger(Loader.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}

Answer 1

I see what you're doing wrong, -- you're calling show, the method that displays the modal dialog before starting the SwingWorker. Again, get the SwingWorker and all wired and running before showing a modal dialog.

Simplified code (with Thread.sleep)

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

import java.util.concurrent.TimeUnit;
import java.lang.reflect.InvocationTargetException;
import java.net.URL;

public class Loader implements Runnable {
    static JFrame frame = new JFrame();
    Frame parentUI = new Frame();
    JDialog dialog = new JDialog();
    JLabel lbl_filename = new JLabel();
    JLabel lbl_path = new JLabel();

    static Loader load = new Loader(null);

    public static void main(String[] args) throws InterruptedException, InvocationTargetException {
        load.run();
        frame.setVisible(true);
    }

    public Loader(Frame parent) {
        init();
        parentUI = parent;
    }

    @Override
    public void run() {
        createDialog(parentUI);
    }

    public final void init() {
        JButton btn = new JButton("Open");

        frame.setTitle("Loader Test");
        frame.setSize(500, 200);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);
        frame.setLayout(new FlowLayout());

        btn.addActionListener(new Action1());

        frame.add(btn);
        frame.add(lbl_filename);
        frame.add(lbl_path);
    }

    class Action1 implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent e) {
            openFile();
        }
    }

    private void createDialog(final Frame parent) {

        dialog.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
        dialog.setModal(true);
        dialog.setTitle("Loader");

        JLabel label = new JLabel("Label");
        dialog.add(label);

        dialog.pack();
        dialog.setLocationRelativeTo(parent);
    }

    public void show(Boolean visible) {
        this.run();
        dialog.setVisible(visible);
    }

    public void close() {
        dialog.setVisible(false);
    }

    private void openFile() {
        System.out.println("Loading file...");

        // !! load.show(true);

        new SwingWorker<Void, Void>() {
            @Override
            protected Void doInBackground() throws Exception {
                // createDoc(path);
                createDoc(null);
                return null;
            };

            @Override
            protected void done() {
                load.close();
            };
        }.execute();

        load.show(true); //!! 
    }

    private void createDoc(String file) {
        try {
            TimeUnit.SECONDS.sleep(4);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}