How can I test that a java applet is loaded using javascript?

Question

The applet is my own, calling ready() simply returns "yes".

First I tried embedding the applet like this:

        <object id="appletIe"
        classid="clsid:8AD9C840-044E-11D1-B3E9-00805F499D93"
        width="100%" height="100%"
        codebase="MyApplet.jar">
        <param name="archive" value="MyApplet.jar" />
        <param name="code" value="MyPackage.Myclass" />
        <param name="myParam" value="My Param Value" />
         <embed id="applet" MAYSCRIPT=true
        type="application/x-java-applet;version=1.6"
        width="1px" height="1px"
        archive="MyApplet.jar"
        code="MyPackage.Myclass"
        pluginspage="http://java.com/download/">
        </object>

I tried to check it was loaded with javascript by calling ready() on document.ready like this: but I immediately got an error (TypeError: $(...).get(...).ready is not a function) so I assume it tried to call the applet ready() function before it loaded.

$(function(){
  if (CheckApplet() == false) {
          $('#appletStatus').html('Failed to load applet.');
      } 
  });



  function CheckApplet() {
      return $('#applet').get(0).ready() == 'yes';
  }

Then I tried loading the applet with jquery like this:

This worked a little better, it did not call the applet ready() function until the applet had loaded. But once in a while it doesn't work, the javascript becomes unresponsive, no error is produced even though the applet seems to be loaded ok.

 $(function(){
  var html = '';

    if ($.browser.msie) {
        html += '<object id="applet" ';
        html += 'classid="clsid:8AD9C840-044E-11D1-B3E9-00805F499D93" ';
        html += 'width="100%" height="100%" ';
        html += 'codebase="MyApplet.jar"> ';
        html += '<param name="archive" value="MyApplet.jar" /> ';
        html += '<param name="code" value="MyPackage.Myclass" /> ';
        html += '<param name="myParam" value="My Param Value" /> ';
        html += '< /object>';
    } else {
        html += '<embed id="applet"';
        html += 'type="application/x-java-applet;version=1.6"';
        html += 'width="1px" height="1px" ';
        html += 'archive="MyApplet.jar"';
        html += 'code="MyPackage.Myclass" ';
        html += 'pluginspage="http://java.com/download/"';
        html += 'myParam="My Param Value" />';
        html += '</embed>';
    }
    $('#myDiv').append(html);

if (CheckApplet() == false) {
          $('#appletStatus').html('Failed to load applet.');
      } 

});

I'm looking for suggestions on how I can improve this, or other ways to achieve the solution.

Answer 1

As you newer know when your applet comes alive (the JVM must be run, the .jar downloaded and run and .ready() must be connected to the browser), it would be a better strategy to let the applet tell the browser when it is ready. It may do that by invoking a JS function named applet_ready() for example.

See here how an applet can invoke JavaScript functions: http://docs.oracle.com/javase/tutorial/deployment/applet/invokingJavaScriptFromApplet.html

Answer 2

I liked dronus's answer but didn't find Oracle's link to be very helpful so here is my full code, which took me a while to sort out (yep, I know, I'm a bit slow).

At the end of the applet class's init() method ('myApplet' in the example):

JSObject window = JSObject.getWindow(this);
Runnable r = new RunJScript(window);
new Thread(r).start();

In a new separate class in the same package as your applet class:

import netscape.javascript.JSObject;

public class RunJScript implements Runnable
{
    private JSObject window;
    public RunJScript(JSObject window) 
    {
        this.window = window;
    }

   public void run() 
   {
        window.call("waitUntilAppletLoaded", null);
   }

}

In the web page header which contains your applet:

<SCRIPT language="javascript">
    timeOut = 0;
    function waitUntilAppletLoaded() 
    {
        if (document.applets['myApplet'].isActive()) 
        {
            // Your actions now that the applet has finished loading.
        }
        else 
        {
            // Increase the timeout by half a second each time round.
            timeOut = timeOut + 500
            settimeout(waitUntilAppletLoaded(),timeOut)
        }
    }
</SCRIPT>

Answer 3

If you don't have access to the applet source code, you can poll for the applet to be loaded before calling methods on it.

Have a look to this answer: https://stackoverflow.com/a/7150084/513173