JWebPresenterSS.java

/*<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
 * Project     : JWebPresenter                                          *
 * Filename    : JWebPresenterSS.java                                   *
 * Introduction: JWebPresenter is a bitmap-image based presenting tool. *
 *               This is a client program, which is a simple solution   *
 *               (series SS), see also series AS (advanced solution).   *
 * Author      : Liang Zhao (writebear \at yahoo \dot com)              *
 * Version     : v1.0  2004/02/29, initial public release               *
 *               v1.01 2004/03/10, remove the (useless) mcMode test     *
 *               v1.1  2004/04/20, change AWT code to JFC (SWING) code! *
 *                                 pop-up menu added.                   *
 *                                 other major changes.                 *
 *               v1.2  2004-05-21, dynamic presenting URLs to treat     *
 *                                 the cache problem more cleverly.     *
 *               v1.21 2004-06-18, add a reset function                 *
 *               v1.22 2004-07-13, documentation improvement.           *
 *                     You can use doxygen doxygen.cfg to get the docs. *
 *               v1.23 2005-01-21, pre-arranged size added, thanks Dave *
 *                                 better command line parameters.      *
 *               v1.3  2005-01-23, browser embed mode, thanks Dave.     *
 * Developed by: Linux, Java 2 SDK SE v1.4.2, etc.                      *
 * Note        : It was originally written in pure AWT code for my PDA  *
 *               (Zaurus SL-C760), but finally I got tired to use some  *
 *               odd features of AWT model such as focus.... Thus from  *
 *               version 1.1 (2004-04-17), I decided to use Swing.      *
 *               v1.0x is based on AWT, though there is no new feature. *
 * Requirement : JRE 1.4 or above with Swing support.                   *
 ************************************************************************
 * Copyright (C) 2004-2005 Liang Zhao                                   *
 *                                                                      *
 * This program is free software; you can redistribute it and/or modify *
 * it under the terms of the GNU General Public License as published by *
 * the Free Software Foundation; either version 2 of the License, or    *
 * (at your option) any later version.                                  *
 *                                                                      *
 * This program is distributed in the hope that it will be useful,      *
 * but WITHOUT ANY WARRANTY; without even the implied warranty of       *
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the        *
 * GNU General Public License for more details.                         *
 *                                                                      *
 * You should have received a copy of the GNU General Public License    *
 * along with this program; if not, write to the Free Software          *
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 *
 * USA, or you can get it from http://www.gnu.org/licenses/gpl.txt      *
 *>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>*/

import java.awt.*;
import java.awt.image.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;
import javax.swing.*;

/**
 * The main class.
 * We basically have two running mode: applet or application.
 * When in applet mode, parameters can be specified by the WWW page
 * where JWebPresenterSS is embeded (see the sample index.html for
 * detailed usage). In application mode, on the other hand, parameters
 * must be given from the command line.
 */
public class JWebPresenterSS extends JApplet {
    /**
     * Version description.
     */
    final static String ver = "JWebPresenter SS 1.3 (2005-01-23), L. Zhao";

    /**
     * Reference to myself (the applet).
     */
    final JApplet me = this;

    /**
     * Reference to the frame instance, valid only for nonempty cmdText.
     */
    JWPFrameSS frame = null;

    /**
     * We can initialize the applet instance by adding a button, which shows
     * the frame when pressed (parameters are passed by JApplet.getParameter()).
     * 2005-01-23 Alternatively, we can show the picture in the viewer (e.g.,
     * browser) with no new window by giving empty (or null) cmdText.
     * @param cmdText text (empty for no window) of the start button, 2005-01-23.
     * @param slideURL URL of the FIRST slide (e.g., http://host/slide-1.png).
     * @param debugMode 0 to disable the debug function, nonzero to enable.
     * @param ctlURL URL for the initial control parameters, see document too.
     *        If given ctlURL is invalid, then slideURL is used repeatedly.
     * @param fetchTime default time interval (in 100ms) to fetch parameters.
     * @param baseURL the base URL, see the note of 2004-04-21.
     * @param windowWidth the width of JWebPresenter window (see NOTICE), 2005-01-20
     * @param windowHeight the height of JWebPresenter window, 2005-01-20
     * <p>NOTICE: 2004-04-21, both slideURL and ctlURL can be (re-)specified
     *            by control parameters Slide and nextCtl (ctlURL) respectively.
     *            They (slideURL and ctlURL) are determined as follows:
     *              If Slide (nextCtl) is an absolute URL, use it;
     *              otherwise use baseURL + Slide (baseURL + nextCtl).</p>
     * <p>NOTICE: 2005-01-20, Dove told me that specifying window size at
     *            start time could be helpful. This is. The default size is
     *            full screen if width or height is invalid.
     */
    public void init() {
        Container pane = getContentPane(); // get the drawing pane.

        String cmdText = me.getParameter("cmdText"); // Get the cmdText string.
        if (cmdText == null) cmdText = "";           // Then cmdText is not null.
        if (cmdText.length() == 0) { // empty string means not to create window.
            pane.add(new JWPPanelSS(null, // no window
                                    me.getParameter("slideURL"),
                                    me.getParameter("debugMode"),
                                    me.getParameter("ctlURL"),
                                    me.getParameter("baseURL"),
                                    me.getParameter("fetchTime"),
                                    true)); // "true" is for applet.
        }
        else { // create the window
            JButton startButton = new JButton(cmdText);
            startButton.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    if (frame == null) {
                        frame = new JWPFrameSS(me.getParameter("slideURL"),
                                               me.getParameter("debugMode"),
                                               me.getParameter("ctlURL"),
                                               me.getParameter("baseURL"),
                                               me.getParameter("fetchTime"),
                                               me.getParameter("windowWidth"),
                                               me.getParameter("windowHeight"),
                                               true); // "true" is for applet.
                    }
                    frame.setVisible(true);
                }
            });
            pane.add(startButton);
        }
    }
    
    /**
     * main function, hence we can also run as an application.
     */
    public static void main(String argv[]) {
        if (argv.length < 1) {
            System.out.println("JWebPresenter Project :: " + ver + "\n"
                + "Usage: java JWebPresenterSS parameters\n"
                + "Parameters can be given like name=value (no space around =) in any order.\n"
                + "  slideURL:  initial URL to get slides, can be omitted if given by ctlURL.\n"
                + "  ctlURL:    initial URL to get control parameters;\n"
                + "  debugMode: debug mode, 0 to disable (default), 1 or above to enable;\n"
                + "  baseURL:   base URL, used if a URL obtained from ctlURL is not absolute;\n"
                + "  fetchTime: time in 100ms to fetch targets (default 50);\n"
                + "  width:     width of presentation window (can be modified after start);\n"
                + "  height:    height of presentation window (can be modified after start).\n"
                + "If no width or height is specified, full screen mode is used.\n"
                + "Parameter's name can be abbreviated if no confusion happens.\n"
                + "For example: s=ftp://host/slide.png c=http://host/ctl.txt b=ftp://host/\n");
            System.exit(1);
        }
        
        String slideURL  = "";
        String ctlURL    = "";
        String debugMode = "";
        String baseURL   = "";
        String fetchTime = "";
        String width     = "";
        String height    = "";

        for (int i=0; i<argv.length; i++) {
            int j = argv[i].indexOf("=");
            if (j == -1) {
                System.out.println("Bad parameter ("+argv[i] +") omitted");
                continue;
            }
            // else {
            switch (argv[i].charAt(0)) {
                case 's' : slideURL  = argv[i].substring(j+1); break;
                case 'c' : ctlURL    = argv[i].substring(j+1); break;
                case 'd' : debugMode = argv[i].substring(j+1); break;
                case 'b' : baseURL   = argv[i].substring(j+1); break;
                case 'f' : fetchTime = argv[i].substring(j+1); break;
                case 'w' : width     = argv[i].substring(j+1); break;
                case 'h' : height    = argv[i].substring(j+1); break;
                default  :
                    System.out.println("Bad parameter ("+argv[i]+") omitted.");
            }
        }

        new JWPFrameSS(slideURL, debugMode, ctlURL, baseURL, fetchTime, width, height, false).setVisible(true);
    }
}

/**
 * The frame class (not used if the applet is embeded in a viewer).
 * <p>We want to show in fullscreen mode, however,
 * it is not possible in Java 1.4. Thus we show a maximized frame.
 */
class JWPFrameSS extends JFrame {
    /**
     * Constructor.
     * @param s String for slideURL.
     * @param d String for debugMode.
     * @param c String for ctlURL.
     * @param b String for baseURL.
     * @param f String for fetchTime.
     * @param w String for width.
     * @param h String for height.
     * @param app true for application, false for applet.
     */
    JWPFrameSS(String s, String d, String c, String b, String f, String w, String h, boolean app) {
        setDefaultCloseOperation(app?DISPOSE_ON_CLOSE:EXIT_ON_CLOSE);

        int width  = 0;
        try {
            width = Integer.parseInt(w);
        }
        catch (NumberFormatException e) {
            width = 0;
        }

        int height = 0;
        try {
            height = Integer.parseInt(h);
        }
        catch (NumberFormatException e) {
            height = 0;
        }

        Dimension screen = Toolkit.getDefaultToolkit().getScreenSize();
        if (width < 1 || width > screen.width) width = screen.width;
        if (height < 1 || height > screen.height) height = screen.height;
        setSize(width, height);

        // Set the window be undecoreated for full screen mode -- require JRE 1.4+.
        if (width == screen.width && height == screen.height) setUndecorated(true);

        getContentPane().add(new JWPPanelSS(this, s, d, c, b, f, app));
   }
}
 
/**
 * The panel class.
 * <p>This is the main part of this program.
 *  A Timer task is performed repeatedly to get control parameters
 *  from ctlURL, and new slide is feteched if needed.</p>
 */
class JWPPanelSS extends JPanel implements ActionListener {
    /**
     * Reference to my ancestor frame (null if embeded in a viewer).
     */
    JFrame frame;

    /**
     * Am I an applet or not? Method quit() depends on it.
     */
    boolean isApplet;

    /**
     * Timer object to control the refresh process.
     */
    Timer timer;

    /**
     * Default toolkit to fetch the slide.
     */
    Toolkit tk;

    /**
     * The base URL (String) for ctlURL and slideURL.
     */
    String baseURL;

    /**
     * The original control URL (given to constructor, used for reset).
     */
    URL orig_ctlURL;

    /**
     * The original slide URL (given to constructor, used for reset).
     */
    URL orig_slideURL;

    /**
     * URL for the control commands.
     */
    URL urlCtl;

    /**
     * URL for the slide image.
     */
    URL urlSlide;

    /**
     * Fetch time interval (in ms!).
     */
    int fetchTime;

    /**
     * Debug mode: true to debug, false to not (2004-04-19).
     */
    boolean debugMode;

    /**
     * Connection object for getting parameters.
     */
    URLConnection c;

    /**
     * Counter for the number of fetched slides.
     */
    int countSlide = 0;

    /**
     * Fetched counter for control parameters.
     */
    int countCtl = 0;

    /**
     * Shall we use advanced mode (= skip slide with the same sequence no.)? See actionPerformed().
     */
    boolean advancedMode;

    /**
     * Image object to hold the target slide.
     */
    Image img;

    /**
     * Mediatracker to get img.
     */
    MediaTracker tracker = new MediaTracker(this);

    /**
     * FastMode setting: if true, fetch ctlURL repeatedly until error (disregard fetchTime);
     * If false, fetch ctlURL repeatedly according to the timer.
     * <p>This is useful for slow clients, who can drop slides to keep up with the latest slide.</p>
     */
    boolean fastMode = false;

    // The follows variables are used in processing control parameters. 

    /**
     * BufferedReader for reading the control parameters from urlCtl.
     */
    BufferedReader in;

    /**
     * Temporary one line text read from in.
     */
    String str;

    /**
     * Version of the command set, valid values are 1, 2...
     */
    int jwpVersion;

    /**
     * Previous sequence number, -1 for none (or nonexist).
     */
    long lastSeq = -1;

    /**
     * Current sequence number, valid values are 0, 1, 2...
     */
    int seq;
    
    // 2004-04-17: add a popup menu to give the user some optional setting.

    /**
     * Popup menu.
     */
    JPopupMenu menu = new JPopupMenu("Popup Menu");

    /**
     * CheckBox menu item to enable/disable the decoration of window.
     * 2005-01-22: all decorate related items are valid only for non-null frame.
     */
    JCheckBoxMenuItem decorateItem;

    /**
     * CheckBox menu item to fill/not fill the image to window.
     */
    JCheckBoxMenuItem fillItem = new JCheckBoxMenuItem("Fill Image to Window");

    /**
     * Show if we should resize the image to fill window.
     */
    boolean bResizeToFill = false;

    /**
     * Show if we should decorate the window.
     * 2005-01-22: all decorate related items are valid only for non-null frame.
     */
    boolean bDecorate;

    /**
     * Information dialog.
     */
    JDialog infoDialog;

    /**
     * Label to show information in infoDialog.
     */
    JLabel infoLabel;

    /**
     * When the name is "More...", show more information.
     */
    JButton moreButton;
    
    /**
     * The debug function (output to err if debugMode is true).
     */
    public void debugMsg(String msg) {
        if (debugMode) System.err.println("(info) " + msg);
    }
    
    /**
     * quit function (hide the frame for applet, otherwise stop the system).
     */
    public void quit() {
        if (isApplet && frame != null) frame.setVisible(false);
        else System.exit(0);
    }
        
    /**
     * Constructor: initializations.
     * @param f JFrame for the ancestor frame instance.
     * @param slide String for slideURL.
     * @param debug String for debugMode.
     * @param ctl String for ctlURL.
     * @param base String for baseURL.
     * @param fetch String for fetchTime.
     * @param app true for application, false for applet.
     */
    JWPPanelSS(JFrame f, String slide, String debug, String ctl, String base, String fetch, boolean app) {
        frame    = f;
        baseURL  = (base==null)?"":base; // non-null for simplicity.
        isApplet = app;
        tk       = Toolkit.getDefaultToolkit();
        
        // Add a hide/exit method: ESC key. This seems not work, why?!!
        addKeyListener(new KeyAdapter() {
            public void keyPressed(KeyEvent e) {
                if (e.getKeyCode() == KeyEvent.VK_ESCAPE) {
                    quit();
                }
            }
        });

        // Mouse triple (not double to avoid mistake) clicks can also quit.
        addMouseListener(new MouseAdapter() {
            public void mouseClicked(MouseEvent e) {
                // 2004-04-21, changed to > 2 to reduce miss operation.
                if (e.getClickCount() > 2)  {
                    quit();
                }
            }
           // Catch the next mouse events to show the popup menu.
            public void mouseReleased(MouseEvent e) {
                if (e.isPopupTrigger()) {
                    menu.show(e.getComponent(), e.getX(), e.getY());
                }
            }
            
            public void mousePressed(MouseEvent e) {
                if (e.isPopupTrigger()) {
                    menu.show(e.getComponent(), e.getX(), e.getY());
                }
            }
        });

        // First, let us get the debugMode. Set false (i.e. no debug) for error.
        try {
            debugMode = (Integer.parseInt(debug) != 0);
        }
        catch (NumberFormatException e) {
            debugMode = false;
        }

        // Get the control URL if it is valid, otherwise null.
        try {
            urlCtl = new URL(ctl);
            orig_ctlURL = urlCtl; // save a copy (!) to orig_ctlURL
        }
        catch (MalformedURLException e) {
            debugMsg("Bad or no ctlURL (" + ctl + "). Set to NONE.");
            orig_ctlURL = null;
            urlCtl      = null;
        }

        // Get the target URL if it is valid, otherwise null.
        try {
            urlSlide = new URL(slide);
            orig_slideURL = urlSlide; // save a copy.
        }
        catch (MalformedURLException e) {
            debugMsg("Bad or no slideURL (" + slide + "). Set to NONE.");
            orig_slideURL = null;
            urlSlide      = null;
        }

        // We can do nothing (thus quit) if both urlCtl and urlSlide are both null.
        if ((urlCtl == null) && (urlSlide == null)) {
            debugMsg("Oops, what can I do for null ctlURL and null slideURL?");
            JButton btnQuit = new JButton("(Invalid input) Check ctlURL and slideURL! (Click to quit)");
            btnQuit.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    quit();
                }
            });
            add(btnQuit);
            return; // Skip other initializations.
        }

        // Get the fetchTime, set to 5s (default) for exception.
        try {
            fetchTime = Integer.parseInt(fetch) * 100;
        }
        catch (NumberFormatException e) {
            debugMsg("Bad or no fetchTime. Set to 5s.");
            fetchTime = 5000;
        }
        
        try {
            debugMsg("Java version = " + System.getProperty("java.version"));
        }
        catch (SecurityException e) {}
        
        debugMsg("--- Parsed parameters are as follows ---\n" +
                 "  slideURL  = " + urlSlide + "\n" +
                 "  debugMode = " + debugMode + "\n" +
                 "  ctlURL    = " + urlCtl + "\n" +
                 "  baseURL   = " + baseURL + "\n" +
                 "  fetchTime = " + fetchTime + "ms\n" +
                 "  Parameters accepted :-).");

        // Add popup menu items.
        // Full screen menu if frame is not null
        if (frame != null) {
            menu.add(new AbstractAction("Full Screen") {
                public void actionPerformed(ActionEvent e) {
                    Dimension screen = tk.getScreenSize();
                    bDecorate = false;      // disable window docoration
                    decorateItem.setSelected(false);
                    bResizeToFill = false;  // disable the fill option
                    fillItem.setSelected(false);
                    frame.dispose(); // we need this to change decoration style
                    frame.setUndecorated(true);
                    frame.setLocation(0, 0);
                    frame.setSize(screen.width, screen.height);
                    setSize(screen.width, screen.height);
                    frame.setVisible(true);
                    repaint();
                }
            });
        }

        /* 2004-06-18: add a reset function which reset urlSlide and
         * urlCtl to orig_slideURL and orig_ctlURL. This may be helpful
         * in trouble, and one does not want to restart the Java VM.
         */
        menu.add(new AbstractAction("Reset (= restore URLs to initial values)") {
            public void actionPerformed(ActionEvent e) {
                urlCtl   = orig_ctlURL;
                urlSlide = orig_slideURL;
                timer.setDelay(fetchTime);  // restart the timer. 
                timer.setInitialDelay(0);
                timer.restart();
                debugMsg("URLs resetted. Starting new fetching...");
            }
        });

        /* 2004-05-21: Zoom in/out seems not useful for presentations.
         * Besides, they require more complicate coding, e.g., mouse handling.
         * Therefore I removed the not-finished zoom function.
         */
        menu.addSeparator();

        // decorate/undecoreate window item
        if (frame != null) {
            decorateItem = new JCheckBoxMenuItem("Decorate Window (then resize, move, etc)");
            bDecorate = !frame.isUndecorated();
            decorateItem.setSelected(bDecorate);
            decorateItem.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    bDecorate = !bDecorate;
                    frame.dispose();
                    frame.setUndecorated(!bDecorate);
                    decorateItem.setSelected(bDecorate);
                    frame.setVisible(true);
                    repaint();
                }
            });
            menu.add(decorateItem);
        }

        fillItem.setSelected(bResizeToFill);
        fillItem.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                bResizeToFill = !bResizeToFill;
                repaint();
            }
        });
        menu.add(fillItem);

        JCheckBoxMenuItem fastItem = new JCheckBoxMenuItem("Fast Mode (= skip intermediate slides)");
        fastItem.setSelected(fastMode);
        fastItem.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                fastMode = !fastMode;
            }
        });
        menu.add(fastItem);

        JCheckBoxMenuItem debugItem = new JCheckBoxMenuItem("Debug to Java Console");
        debugItem.setSelected(debugMode);
        debugItem.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                debugMode = !debugMode;
            }
        });
        menu.add(debugItem);

        menu.addSeparator();
        
        menu.add(new AbstractAction("Information...") {
            public void actionPerformed(ActionEvent e) {
                if (infoDialog != null) infoDialog.setVisible(true);
            }
        });
      
        // quit menu is only available if frame is not null. 
        if (frame != null) { 
            menu.add(new AbstractAction("Quit") {
                public void actionPerformed(ActionEvent e) {
                    quit();
                }
            });
        }

        add(menu);

        // create the information dialog.
        infoDialog = new JDialog(frame, "Information", true);
        Container con = infoDialog.getContentPane();
        infoLabel = new JLabel("<HTML><BR><CENTER><B>"+JWebPresenterSS.ver
            +"</B></CENTER><BR></HTML>", SwingConstants.CENTER);
        con.add(infoLabel);
        JPanel pOK = new JPanel();
        JButton ok = new JButton("OK");
        ok.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                infoDialog.setVisible(false);
                infoLabel.setText("<HTML><BR><CENTER><B>"+JWebPresenterSS.ver
                    +"</B></CENTER><BR></HTML>");
                moreButton.setText("More...");
                infoDialog.pack();
            }
        });
        pOK.add(ok);
        
        moreButton = new JButton("More...");
        moreButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String command = e.getActionCommand();
                
                if (command.equals("More...")) {
                    infoLabel.setText("<HTML><BR><CENTER><B>"+JWebPresenterSS.ver
                        +"</B></CENTER><BR>"
                        +"Base URL = "+baseURL+"<BR>"
                        +"Slide URL = "+((urlSlide==null)?"N/A":urlSlide.toString())+"<BR>"
                        +"Control URL = "+((urlCtl==null)?"N/A":urlCtl.toString())+"<BR>"
                        +"Fetch interval = "+fetchTime+"ms<BR>"
                        +"JWP version = "+((jwpVersion==0)?"N/A":String.valueOf(jwpVersion))+"<BR>"
                        +"Advanced mode = "+(advancedMode?"Enabled":"Disabled")+"<BR>"
                        +"Fetch counter (control/slide) = "+countCtl+"/"+countSlide+"<BR>"
                        +"</HTML>");
                    moreButton.setText("Less...");
                }
                else {
                    infoLabel.setText("<HTML><BR><CENTER><B>"+JWebPresenterSS.ver
                        +"</B></CENTER><BR></HTML>");
                    moreButton.setText("More...");
                }
                infoDialog.pack();
            }
        });
        pOK.add(moreButton);
        
        con.add(pOK, BorderLayout.SOUTH);
        infoDialog.pack();

        debugMsg("Initilization finished. Ready to run...");

        timer = new Timer(fetchTime, this);
        timer.setInitialDelay(0);
        timer.start();
    }

    /**
     * ActionEvent hander, which can happen only for our timer event.
     * @param e ActionEvent.
     * <p>First, we have to get control parameters in order to keep up
     * with the presentation. Second, we get the slide according to
     * control parameters, except for when the frame is not being shown.
     * If fastMode is true, repeat parseCommand() until it returns
     * false, which means an I/O error happened in fetch control parameter
     * (or ctlURL = null. But it is rare). 2004-05-21</p>
     */
    public void actionPerformed(ActionEvent e) {
        int oldFetchTime = fetchTime;
        boolean succ;

        do {
            debugMsg("Time stamp: " + System.currentTimeMillis());
            succ = parseCommands(); // urlSlide, urlCtl, fetchTime, seq may change.
        } while (fastMode & succ);

        // Reschedule if fetch interval (fetchTime) is changed.
        if (fetchTime != oldFetchTime) {
            debugMsg("Fetch timer is re-schduled to " + fetchTime + "ms.");
            timer.setDelay(fetchTime); // restart the timer. 
            timer.restart();
        }
            
        // Skip the slide fetch if frame is non-null but not being shown.
        if (frame != null && !frame.isShowing()) return;

        // 2005-05-18: notice that either urlSlide != null or urlCtl != null.
        // See the constructor JWPPanelSS() and parseCommands().

        if ((advancedMode == true) && (seq == lastSeq)) {
            debugMsg("Target fetch omitted due to the same sequence number.");
        }
        else { // fetch the new slide.
            if (urlSlide == null) return;   // For a bad control parameter Slide.
            countSlide++;                   // Else fetch the slide.
            tracker.removeImage(img);       // Remove to avoid memory leak!
            img = tk.createImage(urlSlide); // createImage has no cache problem
            tracker.addImage(img, 0);       // Use tracker to watch the load.
            try { tracker.waitForID(0); }
            catch (InterruptedException ie) {
                debugMsg("Interrupted in loading image from "+urlSlide);
                tracker.removeImage(img);   // For interrupted load, remove it.
                img = null;                 // And set the image to null.
            }
            if (img == null) {              // For any error,
                debugMsg("Target fetch failed (count = " + countSlide + ").");
            } else {                        // Otherwise,
                debugMsg("Target fetch succeeded (count = " + countSlide + ").");
                if (advancedMode == true) { lastSeq = seq; }
                repaint();
            }
        }
    }
    
    /**
     * paintComponent (draw the image at the center after download finishes).
     * @param g Graphics to draw the image.
     * <p>The text drawing position (15, 15) is rather dirty. I'd like to improve if I have more time.
     */
    public void paintComponent(Graphics g) {
        super.paintComponent(g);

        if (img == null) { // only happens for error including remote not ready.
            debugMsg("No image is available for painting!");
            g.drawString("No image! Error or remote not ready?", 15, 15);
            return;
        }
        
        if (tracker.statusAll(false) == MediaTracker.COMPLETE) {
            if (bResizeToFill == false) {
                int upper_left  = (getWidth() - img.getWidth(this)) >> 1;
                int lower_right = (getHeight() - img.getHeight(this)) >> 1;
                g.drawImage(img, upper_left, lower_right, this);
            } else {
                g.drawImage(img, 0, 0, getWidth(), getHeight(), this);
            }
        }
        else {
            debugMsg("Painted image is not ready!");
            g.drawString("Waiting for the load of image...", 15, 15);
        }
    }

    /**
     * Get the unsigned int parameter.
     * @param msg String for the message to extract.
     * @param pattern String for the pattern to handle.
     * @return int of the result, negative for errors.
     * <p>msg should be in "pattern=value" format (NO space before and after =).</p>
     */
    public static int getUInt(String msg, String pattern) {
        int value = -1; // -1 shows error.
        
        if (msg.startsWith(pattern+"=") == true) {
            try {
                value = Integer.parseInt(msg.substring(msg.indexOf("=")+1));
            }
            catch (NumberFormatException e) {
                value = -1; // -1 means error.
            }
        }
        return value;
    }
    
    /**
     * Get the URL parameter, null for errors.
     * @param msg String for the message to extract.
     * @param pattern String for the pattern to handle.
     * @return URL for the result, null for errors.
     * <p>msg should be in "pattern=value" format. We use baseURL!</p>
     */
    public URL getURL(String msg, String pattern) {
        URL u = null;
        
        if (msg.startsWith(pattern+"=") == true) {
            try { u = new URL(msg.substring(msg.indexOf("=")+1)); }
            catch (MalformedURLException e) { u = null; }
            // In case of error, we try to use baseURL as the base.
            if (u == null) {
                try {
                    u = new URL(baseURL + msg.substring(msg.indexOf("=")+1));
                }
                catch (MalformedURLException e) { u = null; }
            }
        }
        return u;
    }
      
    /**
     * Parse the control parameters by a connection.
     * @return true for success, false for failure.
     * <p>It sets advancedMode to true for valid descriptions.
     * Besides, any old value is not changed if new value is invalid.
     */
    private boolean parseCommands() {
        int v, s, t;    // temporary variables for jwpVersion, seq and fetchTime
        URL cURL, sURL; // temporary variables to find the ctlURL and slideURL
        
        advancedMode = false;
        if (urlCtl == null) return false; // return (advancedMode is thus false)
       
        advancedMode = true; // Must set to true as ctlURL may not be ready.
        countCtl++;
        try {
            c = urlCtl.openConnection();
            c.connect();
            in = new BufferedReader(new InputStreamReader(c.getInputStream()));
            debugMsg("Parsing the control commands ...");
            v = s = t = -1;  // initialize temporary variables
            cURL = sURL = null;
            while ((str = in.readLine()) != null) {
                debugMsg("Remote control paramters>> " + str);
                if (sURL == null) sURL = getURL(str, "Slide");
                if (cURL == null) cURL = getURL(str, "NextCtl");
                str = str.trim().toLowerCase(); // URL is case sensitive, but...
                // Find valid descriptions for jwpVersion, Seq and fetchTime.
                if (v < 1) v = getUInt(str, "jwpversion");
                if (s < 0) s = getUInt(str, "seq");
                if (t < 0) t = getUInt(str, "fetchtime");
            }
            if (v >= 1)     jwpVersion = v;     // renew the version
            if (s >= 0)     seq        = s;     // renew the seq
            if (t >= 1)     fetchTime  = t*100; // renew the fetch time
            if (cURL != null) urlCtl   = cURL;  // renew the urlCtl
            if (sURL != null) urlSlide = sURL;  // renew the urlSlide
            // Turn off the advanced mode here for invalid parameters only.
            if ((v < 1) || (s < 0)) advancedMode = false;
        }
        catch (IOException e) {
            debugMsg("IO error in reading from " + urlCtl);
            return false;
        }
        debugMsg("*** Settings after parsing control command ***\n" +
                 "  JWPVersion = " + jwpVersion + "\n" +
                 "  Seq = " + seq + "\n" +
                 "  FetchTime = " + fetchTime+ "ms\n" +
                 "  Slide = " + urlSlide + "\n" +
                 "  NextCtl = " + urlCtl +
                 (advancedMode?"":"\n  Advanced mode disabled."));
        return true;
    }
}

---