Very slow GUI in web browser application

Question

Hello,
I am trying to write a web browser application and I have a problem with the GUI. When the page is being loaded and set on the JEditorPane the GUI becomes very slow (actually it freezes). I don't know if this happens because of my swing implementation or because I am not using threads properly.
I use the SwingWorker class. I created a worker thread which loads the web page and then sets it to the JEditorPane.
Could you give me some ideas please? Below are some parts of my code.
Thank you
public class BrowserFrame extends javax.swing.JFrame {
    /** Creates new form BrowserFrame */
    public BrowserFrame() {
        initComponents();
        loadUrlsFromHistoryFile();
    private class RetrievePageTask extends SwingWorker<Void, URL> {
        private String address = null;
        RetrievePageTask(String address) {
            this.address = address;
            pageLoadProgressBar.setIndeterminate(true);
        protected Void doInBackground() {
            URL url = null;
            try {
                url = new URL(address);
                publish(url);
            catch(MalformedURLException exc) {
                System.out.println(exc);
            catch(IOException exc) {
                System.out.println(exc);
            return null;
        protected void process(List<URL> url) {
            try {
                pageEditorPane.setPage(url.get(url.size() - 1));
            catch(IOException exc) {
                System.out.println(exc);
            String url_str = url.get(url.size() - 1).toString();
            addressComboBox.setSelectedItem(url_str);
            addUrlToAddressComboBox(url_str);
    private void addressComboBoxItemStateChanged(java.awt.event.ItemEvent evt) {                                                
        // Get the affected item
        Object item = evt.getItem();
        if(evt.getStateChange() == java.awt.event.ItemEvent.SELECTED) {
            // Item was just selected
            if(item.toString().equalsIgnoreCase(""))
                return;
            RetrievePageTask retrievePageTask = new RetrievePageTask(item.toString());
            retrievePageTask.execute();
        else if(evt.getStateChange() == java.awt.event.ItemEvent.DESELECTED) {
            // Item is no longer selected
            System.out.println("\nItem: " + item + " is no longer selected");           
    private void addressComboBoxActionPerformed(java.awt.event.ActionEvent evt) {                                               
        if ("comboBoxEdited".equals(evt.getActionCommand())) {
            // User has typed in a string; only possible with an editable combobox
            goButtonActionPerformed(evt);
        else if ("comboBoxChanged".equals(evt.getActionCommand())) {
            // User has selected an item; it may be the same item
            System.out.println("\nSpot TWO");
    private void goButtonActionPerformed(java.awt.event.ActionEvent evt) {
         RetrievePageTask retrievePageTask = new RetrievePageTask(address);
         retrievePageTask.execute();
    private void pageEditorPaneHyperlinkUpdate(javax.swing.event.HyperlinkEvent evt) {                                              
        if(evt.getEventType() == javax.swing.event.HyperlinkEvent.EventType.ACTIVATED) {
             RetrievePageTask retrievePageTask = new RetrievePageTask(evt.getURL().toString());
            retrievePageTask.execute();
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                BrowserFrame surfRider = new BrowserFrame();
                surfRider.setVisible(true);
}

Answer 1

Now it is all.
package webbrowser;
import java.net.*;
import java.io.*;
import java.util.*;
import javax.swing.*;
public class BrowserFrame extends javax.swing.JFrame {
    /** Creates new form BrowserFrame */
    public BrowserFrame() {
        initComponents();
        loadUrlsFromHistoryFile();
    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
    // <editor-fold defaultstate="collapsed" desc=" Generated Code ">                         
    private void initComponents() {
        addressLabel = new javax.swing.JLabel();
        goButton = new javax.swing.JButton();
        jScrollPane1 = new javax.swing.JScrollPane();
        pageEditorPane = new javax.swing.JEditorPane();
        jButton1 = new javax.swing.JButton();
        jButton2 = new javax.swing.JButton();
        jButton3 = new javax.swing.JButton();
        homeButton = new javax.swing.JButton();
        refreshButton = new javax.swing.JButton();
        addressComboBox = new javax.swing.JComboBox();
        jLabel1 = new javax.swing.JLabel();
        statusLabel = new javax.swing.JLabel();
        pageLoadProgressBar = new javax.swing.JProgressBar();
        menuBar = new javax.swing.JMenuBar();
        fileMenu = new javax.swing.JMenu();
        openFileMenuItem = new javax.swing.JMenuItem();
        exitMenuItem = new javax.swing.JMenuItem();
        viewMenu = new javax.swing.JMenu();
        historyMenuItem = new javax.swing.JMenuItem();
        pageSourceMenuItem = new javax.swing.JMenuItem();
        toolsMenu = new javax.swing.JMenu();
        preferencesMenuItem = new javax.swing.JMenuItem();
        helpMenu = new javax.swing.JMenu();
        aboutMenuItem = new javax.swing.JMenuItem();
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setTitle("Surf Rider");
        setName("browserFrame");
        addWindowListener(new java.awt.event.WindowAdapter() {
            public void windowClosing(java.awt.event.WindowEvent evt) {
                formWindowClosing(evt);
        addressLabel.setHorizontalAlignment(javax.swing.SwingConstants.RIGHT);
        addressLabel.setText("Address:");
        goButton.setText("GO");
        goButton.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                goButtonActionPerformed(evt);
        pageEditorPane.setEditable(false);
        pageEditorPane.setContentType("text/html");
        pageEditorPane.addHyperlinkListener(new javax.swing.event.HyperlinkListener() {
            public void hyperlinkUpdate(javax.swing.event.HyperlinkEvent evt) {
                pageEditorPaneHyperlinkUpdate(evt);
        jScrollPane1.setViewportView(pageEditorPane);
        jButton1.setText("Back");
        jButton1.setEnabled(false);
        jButton2.setText("Forth");
        jButton2.setEnabled(false);
        jButton3.setText("Stop");
        jButton3.setEnabled(false);
        homeButton.setText("Home");
        homeButton.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                homeButtonActionPerformed(evt);
        refreshButton.setText("Refresh");
        refreshButton.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                refreshButtonActionPerformed(evt);
        addressComboBox.setEditable(true);
        addressComboBox.addItemListener(new java.awt.event.ItemListener() {
            public void itemStateChanged(java.awt.event.ItemEvent evt) {
                addressComboBoxItemStateChanged(evt);
        addressComboBox.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                addressComboBoxActionPerformed(evt);
        jLabel1.setText("Browser status: ");
        statusLabel.setText("Current status");
        pageLoadProgressBar.setBorder(javax.swing.BorderFactory.createEtchedBorder());
        fileMenu.setText("File");
        fileMenu.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                fileMenuActionPerformed(evt);
        openFileMenuItem.setLabel("Open File...");
        openFileMenuItem.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                openFileMenuItemActionPerformed(evt);
        fileMenu.add(openFileMenuItem);
        exitMenuItem.setLabel("Exit");
        fileMenu.add(exitMenuItem);
        menuBar.add(fileMenu);
        viewMenu.setText("View");
        viewMenu.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                viewMenuActionPerformed(evt);
        historyMenuItem.setLabel("History");
        viewMenu.add(historyMenuItem);
        pageSourceMenuItem.setLabel("Page Source");
        viewMenu.add(pageSourceMenuItem);
        menuBar.add(viewMenu);
        toolsMenu.setText("Tools");
        preferencesMenuItem.setLabel("Preferences");
        toolsMenu.add(preferencesMenuItem);
        menuBar.add(toolsMenu);
        helpMenu.setText("Help");
        aboutMenuItem.setLabel("About");
        helpMenu.add(aboutMenuItem);
        menuBar.add(helpMenu);
        setJMenuBar(menuBar);
        org.jdesktop.layout.GroupLayout layout = new org.jdesktop.layout.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
            .add(org.jdesktop.layout.GroupLayout.TRAILING, layout.createSequentialGroup()
                .add(jButton1)
                .addPreferredGap(org.jdesktop.layout.LayoutStyle.RELATED)
                .add(jButton2)
                .add(6, 6, 6)
                .add(refreshButton)
                .addPreferredGap(org.jdesktop.layout.LayoutStyle.RELATED)
                .add(jButton3)
                .addPreferredGap(org.jdesktop.layout.LayoutStyle.RELATED)
                .add(homeButton)
                .addPreferredGap(org.jdesktop.layout.LayoutStyle.RELATED)
                .add(addressLabel, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, 56, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(org.jdesktop.layout.LayoutStyle.RELATED)
                .add(addressComboBox, 0, 568, Short.MAX_VALUE)
                .addPreferredGap(org.jdesktop.layout.LayoutStyle.RELATED)
                .add(goButton))
            .add(jScrollPane1, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, 1008, Short.MAX_VALUE)
            .add(layout.createSequentialGroup()
                .addContainerGap()
                .add(jLabel1)
                .addPreferredGap(org.jdesktop.layout.LayoutStyle.RELATED)
                .add(statusLabel, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, 339, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(org.jdesktop.layout.LayoutStyle.RELATED, 470, Short.MAX_VALUE)
                .add(pageLoadProgressBar, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE))
        layout.setVerticalGroup(
            layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
            .add(layout.createSequentialGroup()
                .addContainerGap()
                .add(layout.createParallelGroup(org.jdesktop.layout.GroupLayout.BASELINE)
                    .add(goButton)
                    .add(jButton1)
                    .add(jButton2)
                    .add(homeButton)
                    .add(jButton3)
                    .add(refreshButton)
                    .add(addressLabel)
                    .add(addressComboBox, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE))
                .addPreferredGap(org.jdesktop.layout.LayoutStyle.RELATED)
                .add(jScrollPane1, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, 601, Short.MAX_VALUE)
                .addPreferredGap(org.jdesktop.layout.LayoutStyle.RELATED)
                .add(layout.createParallelGroup(org.jdesktop.layout.GroupLayout.TRAILING)
                    .add(layout.createParallelGroup(org.jdesktop.layout.GroupLayout.BASELINE)
                        .add(jLabel1)
                        .add(statusLabel, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, 15, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE))
                    .add(pageLoadProgressBar, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE)))
        java.awt.Dimension screenSize = java.awt.Toolkit.getDefaultToolkit().getScreenSize();
        setBounds((screenSize.width-1016)/2, (screenSize.height-724)/2, 1016, 724);
    }// </editor-fold>                       
    private class RetrievePageTask extends SwingWorker<Void, URL> {
        private String address = null;
        RetrievePageTask(String address) {
            this.address = address;
            pageLoadProgressBar.setIndeterminate(true);
        public String getAddress() {
            return address;
        public void setAddress(String newAddress) {
            address = newAddress;
        protected Void doInBackground() {
            URL url = null;
            try {
                url = new URL(address);
                publish(url);
            catch(MalformedURLException exc) {
                System.out.println(exc);
            catch(IOException exc) {
                System.out.println(exc);
            return null;
        protected void process(List<URL> url) {
            try {
                System.out.println("\nBefore setting the editorPane");
                pageEditorPane.setPage(url.get(url.size() - 1));
            catch(IOException exc) {
                System.out.println(exc);
            String url_str = url.get(url.size() - 1).toString();
            url_str = url_str.toLowerCase(); // URL string is turned in lower case
            addressComboBox.setSelectedItem(url_str);
            addUrlToAddressComboBox(url_str);
            pageLoadProgressBar.setIndeterminate(false);
    private void openFileMenuItemActionPerformed(java.awt.event.ActionEvent evt) {                                                
// TODO add your handling code here:
    private void viewMenuActionPerformed(java.awt.event.ActionEvent evt) {                                        
// TODO add your handling code here:
    private void fileMenuActionPerformed(java.awt.event.ActionEvent evt) {                                        
// TODO add your handling code here:
    private void refreshButtonActionPerformed(java.awt.event.ActionEvent evt) {                                             
    // Action performed when homeButton's Action Listener listens to an event. This
    // event is passed here as a parameter (evt). The selected item of the addressComboBox is
    // set to be the homePage. The browser goes to the home page.
    private void homeButtonActionPerformed(java.awt.event.ActionEvent evt) {                                          
        addressComboBox.setSelectedItem(homePage);
    // This method loads the URL history from the history.txt file into the vector and into the
    // addressComboBox.
    private void loadUrlsFromHistoryFile() {
        BufferedReader inputStream = null;
        addressComboBox.setSelectedItem(homePage);
        try {
            inputStream = new BufferedReader(new FileReader("history.txt"));
            String tmp;
            while((tmp = inputStream.readLine()) != null) {
                // Adding url to history_mem vector
                historyMem.add(tmp);
                // Adding url to addressComboBox
                addressComboBox.addItem(tmp);
        catch(IOException exc) {
            System.out.println(exc);
    private void addressComboBoxItemStateChanged(java.awt.event.ItemEvent evt) {                                                
        // Get the affected item
        Object item = evt.getItem();
        if(evt.getStateChange() == java.awt.event.ItemEvent.SELECTED) {
            // Item was just selected
            System.out.println("\nItem: " + item + " was just selected");
            if(item.toString().equalsIgnoreCase(""))
                return;
            RetrievePageTask retrievePageTask = new RetrievePageTask(item.toString());
            retrievePageTask.execute();
        else if(evt.getStateChange() == java.awt.event.ItemEvent.DESELECTED) {
            // Item is no longer selected
            System.out.println("\nItem: " + item + " is no longer selected");           
    // Action performed when an event occurs in the addressComboBox (eg Pressing enter
    // after typing the address).
    private void addressComboBoxActionPerformed(java.awt.event.ActionEvent evt) {                                               
        if ("comboBoxEdited".equals(evt.getActionCommand())) {
            // User has typed in a string; only possible with an editable combobox
            goButtonActionPerformed(evt);
        else if ("comboBoxChanged".equals(evt.getActionCommand())) {
            // User has selected an item; it may be the same item
    // Action performed when goButton's Action Listener listens to an event. This
    // event is passed here as a parameter (evt). When a valid URL is inserted, the
    // pageEditorPane is set to that URL.
    private void goButtonActionPerformed(java.awt.event.ActionEvent evt) {                                        
        // 6 spaces added to the address. This is done for control reasons. Below we
        // use substring which causes exception when those spaces do not exist.
        String address = addressComboBox.getSelectedItem() + "      ";
        if(addressComboBox.getSelectedItem() == null || address.equalsIgnoreCase("      ") || address.equalsIgnoreCase("http://      ")) {
            JOptionPane.showMessageDialog(null, "No address specified.", "No address", javax.swing.JOptionPane.ERROR_MESSAGE);
        else {
            if(!address.substring(0, 7).equalsIgnoreCase("http://"))
                address = "http://" + address;
                RetrievePageTask retrievePageTask = new RetrievePageTask(address);
                retrievePageTask.execute();
    // Action performed when closing the form window
    private void formWindowClosing(java.awt.event.WindowEvent evt) {                                  
        try {
            addUrlsToHistoryFile(historyMem);
        catch(IOException exc) {
            System.out.println(exc);
    /* This method is used to handle the case in which the user clicks on a hyperlink.
     In this case the pageEditorPane must present the contents of the URL that was
     clicked. This URL is retrieved from the evt object (which is a parameter to this
     method) with the method getURL().
    private void pageEditorPaneHyperlinkUpdate(javax.swing.event.HyperlinkEvent evt) {                                              
        if(evt.getEventType() == javax.swing.event.HyperlinkEvent.EventType.ACTIVATED) {
             RetrievePageTask retrievePageTask = new RetrievePageTask(evt.getURL().toString());
            retrievePageTask.execute();
    // This method adds the visited URLs to the addressComboBox's item list. It takes as a
    // parameter the URL which is going to be added. If the URL is already in the list, then
    // it is not added again.
    private void addUrlToAddressComboBox(String url_str) {
        // number of items in the combo box's list
        int itemCount = addressComboBox.getItemCount();
        for(int i = 0; i < itemCount; i++) {
            if(url_str.equalsIgnoreCase((String)addressComboBox.getItemAt(i)))
                return;
        addressComboBox.addItem(url_str);
        historyMem.add(url_str);
    // This method adds the visited URLs to the history file. It takes as a parameter the URL
    // which is going to be added.
    private void addUrlsToHistoryFile(Vector url_history) throws IOException {
        PrintWriter outputStream = null;
        try {
            outputStream = new PrintWriter(new FileWriter("history.txt"));
            for(int i = 0; i < url_history.size(); i++)
                outputStream.println((String)url_history.get(i));
        finally {
            if(outputStream != null) {
                outputStream.close();
     * @param args the command line arguments
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                BrowserFrame surfRider = new BrowserFrame();
                surfRider.setVisible(true);
    // Variables declaration - do not modify                    
    private javax.swing.JMenuItem aboutMenuItem;
    private javax.swing.JComboBox addressComboBox;
    private javax.swing.JLabel addressLabel;
    private javax.swing.JMenuItem exitMenuItem;
    private javax.swing.JMenu fileMenu;
    private javax.swing.JButton goButton;
    private javax.swing.JMenu helpMenu;
    private javax.swing.JMenuItem historyMenuItem;
    private javax.swing.JButton homeButton;
    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    private javax.swing.JButton jButton3;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JMenuBar menuBar;
    private javax.swing.JMenuItem openFileMenuItem;
    private javax.swing.JEditorPane pageEditorPane;
    private javax.swing.JProgressBar pageLoadProgressBar;
    private javax.swing.JMenuItem pageSourceMenuItem;
    private javax.swing.JMenuItem preferencesMenuItem;
    private javax.swing.JButton refreshButton;
    private javax.swing.JLabel statusLabel;
    private javax.swing.JMenu toolsMenu;
    private javax.swing.JMenu viewMenu;
    // End of variables declaration                  
    // Variables decleration - able to modify
    private Vector<String> historyMem = new Vector<String>();
    private String homePage = "http://www.kaissa.gr";
    // End of variables decleration
    // PUBLIC METHODS
    // Get and Set methods for the private variables declared above
    public Vector getHistoryMem() {
        return historyMem;
    public void setHistoryMem(Vector<String> newHM) {
        historyMem = newHM;
    public String getHomePage() {
        return homePage;
    public void setHomePage(String newHP) {
        homePage = newHP;
}