Browser Inter-Tab communication via Applet

"Richard Maher" <>
Mon, 16 Mar 2009 18:50:47 +0800

For some time (ever since a guy called Bojan Nemec told me about it :-) I've
been toying with the idea of my Java Applet declaring its TCP/IP Socket as a
static class-variable instead of an instance-variable, and on each
invocation (new page, new tab, or new browser) the init() would check to see
if the Socket was already connected (and in my case User Authorization
completed) and, if so, skip that bit. Where I think it would be useful is
when there is a Control-Panel/Dashboard requirement, similar to what Arne
and another poster were discussing recently, where each browser "tab" was a
different set of instrumentation/view. All pages being servered by a single,
secure, feature-rich, connection-oriented, context-laden, and
high-performance Socket.

NB: If this is simply *just not doable* then please let me know now before I
spend a few days trying to get it to work :-)

Some issues that spring to mind (that I hope someone can offer advice on)
are: -

1) To continue my "single reader-thread to oodles of writer-threads" model,
I'm really hoping that JSObject.getWindow() will return something that is
both unique to each web-page instance (wherever it is hosted) and the
accessible from my single reader thread. I plan to store it in a Linked-List
along with a Unique Id that will accompany the user request-messages on
their trips to the server and when they comes back, I'll search the list for
matching index-number, get the corresponding JSObject, and then perform the (Perhaps JSObject is serializable? No wait - there's a toString()
method! What's the reverse? I'm guessing you can't simply cast the String as

2) I hope that JSObject.getWindow() returns the same thing in the Applet's
destroy() method as it does in the int() method so that I can do a reverse
lookup. Hey, there's a JSObject.equals() method - You bewdy!

3) The whole concept of Socket-Hijacking a la mode de Session-Hijacking, I'm
gonna leave to one side for the moment. I'm relying on Java to prohibit the
manual construction/fudge of a Java Socket on top of just any old socket,
and the operating system to protect a socket in one process/image from
access by another unprivileged process/image.

4) How do I prevent just any old page from including an <object> tag for my
Applet and gaining access to the (possibly pre-authorized) Socket? Off the
top of my head, I could store the Document Base of the first page that
actually passed authentication, and if any subsequent page comes from a
different DB then prompt for username/password again. Any other tools in the
toolbox that I can use to secure access?

5) I'll have to introduce a logout function as that functionality is
currently enforced automatically by any page-change. I guess a dialog box
with some useless Socket statistics and a logout button should suffice.
(When the number of JSObjects is reduced to zero, an automatic logout will
take place.)

6) JRE instances. Funny how IE and FF don't share the same JRE instance :-)
Even with Java 6 and up, as long as the Applets ask for the same Java
version then can there be every expectation that they'll share the same JRE

7) Anything else?

Cheers Richard Maher

PS. Which Frame does the activate in (let's say there is a
function with the same name in each frame of a 3-frame frameset? Current?
Top? Different JSObject.getWindow() result for each frame?

"Richard Maher" <> wrote in message


I replaced the pilot-error: -
    public void javaMethod (String jsNum, String jsFunc) {
    public void javaMethod (String jsNum, Object jsFunc) {

and it seems to be giving me a bit more. Sorry for the distraction.

Cheers Richard Maher

"Richard Maher" <> wrote in message


Using netscape.javascript.JSObject (LiveConnect) I want/need to pass a
Function Reference to my Java Applet so that it can either call that
directly, or pass it to a static JavaScript function that will then


the call to the appropriate anonymous function that formed a closure.

Please forgive me if the terminology is not strictly correct, but I hope


can still understand what I'm trying to do.

I thought the second argument to could be an array of


*or* Objects but trying to get a JavaScript object (or a


to it) to survive the Java Applet membrane (without some sort of
serialize/deserialize) is proving difficult. Am I missing something


Does anyone have a small example I can look at?

Maybe it's as easy as the first argument to can be a
JavaScript VARiable? I'll give it a go. . .

Cheers Richard Maher

//This is called from the "onload" event
    function load() {
      myFunc = setClosure();
      chan = document.getElementById("AnonCallApplet");
// This is called from the Applet
    function jsMethod(javaInt, javaFunc) {
      alert('Integer ' + javaInt);
      alert('JavaFunc ' + javaFunc.toString());

    function setClosure() {
      var lclNum = 0;
      return function(){
                alert("lclNum = " + lclNum);
// This is called by some user-driven event (onchange, onclick. . ).
    function callApplet() {
      chan.javaMethod(step, myFunc)
      return true;

//Here's the Applet

import java.applet.Applet;
import netscape.javascript.JSObject;
import netscape.javascript.JSException;

public class AnonCallApplet extends Applet {

    private JSObject browser;
    private static int sumNum = 0;
    private int addNum;

    public void init(){
        try {
            browser = JSObject.getWindow(this); }
        catch (netscape.javascript.JSException e) {
            e.printStackTrace(); }
        catch (Exception e) {
            e.printStackTrace(); }

    public void javaMethod (String jsNum, String jsFunc) {

        addNum = Integer.parseInt(jsNum);

        sumNum += addNum;
        Object args[] = {(Object)new Integer(sumNum), (Object)jsFunc};
        try {
  "jsMethod", args);}
        catch (JSException e){
            System.out.println("Error when calling jsMethod()"); }

    public void destroy() {

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