http://www.pinlady.net/PluginDetect/JavaDetect.htm

It turns out that for the newer versions of Sun Java, one can detect the JRE very quickly in Internet Explorer without starting up the full JRE.

Older JRE versions are a different story.

Here are a few comments/tests regarding Java that I have so far:
http://www.pinlady.net/test/PluginDetect.htm

If you put Java detection on your page, it looks to the user like your page never loads. Many people don’t have the patience for that, and will just leave your site.

You might be better off using Flash for displaying videos, as opposed to Java.

So the question is what is more annoying. Having your home page appear that it doesn’t ever load (in reality a bad delay due to Java startup), or having a message popup saying ’sorry’ when they click on a link to see your video.

It is my conclusion that there is no way in IE to detect Java without starting it up. But that statement must be qualified.

Prior to IE 7, you could look for certain ActiveX objects like “JavaWebStart.isInstalled”
which would not start Java, and would tell you the Java Family version present.

However, IE 7 has made plugin detection for Java (and QuickTime) alot more difficult. All ActiveX objects are deactivated by default, meaning they won’t work the first time unless the user clicks on that yellow security popup the first time.

There are only a small number of pre-approved ActiveX controls that never give that popup.

So, for IE

For IE 7, the best I can do is try to detect some minimum version of Java. If Java is min version, then Java starts up.

I have spent the last year trying to find ways to detect Java. And there are no simple answers.

How about you do Java detection only after someone asks to see the video? If Java is present, the Java detection starts up Java…but so what since you are going to be using Java anyway to display the video.

If Java is not present, no big deal. No startup delay since it is not installed.

Also it is usually IE that starts up Java during detection, not other browsers.

These scripts need tweaking to apply to your situation, in my case I was sniffing for 1.4 support.
—- from checkjava.js (firefox /netscape compatible) ————
var supports14 = false;
function checkJava() {
// Firefox
if ( navigator.plugins && navigator.plugins.length > 0 ) {
nps = navigator.plugins;
for ( i = 0; i = 0 ) {
idx = mtype.type.indexOf(”version=”);
if ( idx > 0 ) {
version = mtype.type.substr( idx + 8, 3 );
if ( version == “1.4″ ) { supports14 = true; break; }
}
}
}
}
}
}

———- from checkjava.vbs (for IE) —————————–
‘* Note that is_ie has been previously defined, prolly based on User-Agent string
on error resume next
If is_ie Then
If Not(IsObject(CreateObject(”JavaWebStart.isInstalled”))) Then
javawsInstalled = 0
Else
javawsInstalled = 1
End If
If Not(IsObject(CreateObject(”JavaWebStart.isInstalled.1.4.2.0″))) Then
javaws142Installed = 0
Else
javaws142Installed = 1
End If
If Not(IsObject(CreateObject(”JavaWebStart.isInstalled.1.5.0.0″))) Then
javaws150Installed = 0
Else
javaws150Installed = 1
End If
supports14 = javaws150Installed Or javaws142Installed
End If

‘* needs updating for java 1.6

should do the trick. I’m not totally sure it works in all browsers, though, and it merely states that Java is available, not that it is already running.