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Editorial Team
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Asked: 2026-05-15T07:16:53+00:00

This is driving me up the wall. I have checked and rechecked spelling and

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This is driving me up the wall. I have checked and rechecked spelling and paths. I have tried just about every combination of paths, including relative, absolute, and full http paths. I continue to get the following error when trying to load a Java applet:

java.lang.ClassNotFoundException: AppletClient.class
    at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Exception: java.lang.ClassNotFoundException: AppletClient.class

The HTML used to load the applet:

<applet width="100" height="100" archive="applet/myapplet.jar, applet/applet_dependency.jar" code="AppletClient.class">
    <param value="blahblah" name="username">
    <param value="false" name="codebase_lookup">
</applet>

The applet is in a relative directory, “applet”, from the path of the current page. I have unzipped the jar file and can see AppletClient.class. Also, in the source of the project, it is spelled that way (casing and all). I have tried with/without the parameters. I have changed the names of the archive jars in the applet include tag just to see if I get a different error for bad file names (same error).

I have manually done GETs on the jars to make sure the server is responding to the requests (it is).

I have tried with and without the codebase tag, with all different varieties of paths (start getting bad “magic number” errors on those).

I know that this error sometimes pops up when a dependency fails to load, so it can be misleading, but all dependencies are present, accounted for, and are fetchable via manual GETs.

Between each and every attempt I always clear my cache in FireFox. These problems are reproduced in IE8 and Chrome as well.

Per my Java Console from the browser, I am running Java Plug-in 1.6.0_20. This is from the same machine that I develop the applet on, which runs fine via Eclipse.

Finally, I kicked on Fiddler2, and I don’t see a single request for the jar files anywhere The host site is running from my Visual Studio debugger, so it’s running on localhost. But I see the requests for all the other resources on Fiddler. Just… no Jars. ANYWHERE. I clear the log, cleared my browser cache, and did a ctrl-R refresh. And still, not a single Jar request on the Fiddler log.

I even did a delayed write (with JS) of the applet tag after the page loaded, once all the Fiddler activity slowed down. The element gets written to the document (and I can see the 100×100 Java error window), but not a single request shows up on Fiddler.

Any suggestions, before I go crawl into the corner and cry myself to sleep?

EDIT: From the Java console, if I hit “l” (el) to “dump classloader list”, I see something that looks like this:

Live entry: key=http://localhost:55446/BaseWebSite/,http://localhost:55446/BaseWebSite/applet/myappliet.jar, http://localhost:55446/BaseWebSite/applet/applet_dependency.jar, refCount=1, threadGroup=sun.plugin2.applet.Applet2ThreadGroup[name=http://localhost:55446/BaseWebSite/-threadGroup,maxpri=4]

EDIT 2: The applet does some networking (Jabber/XMPP), so I did a self-signed cert to see if that helped. Get prompted regarding the self signed cert – so it’s reading something – but still doesn’t work. And it is not showing up in the Java cache file list… and still nothing on Fiddler.

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1 Answer

  1. Editorial Team

    It turns out my problem was actually a combination of problems. I would temporarily solve one, but since that didn’t work (since there were other problems), I would revert back and try another approach.

    I’ve tried so many different things here that I’m not sure what the exact fix was. But, I think what it boiled down to was

    1) Since my applet uses networking components (Jabber/XMPP), it needed to be signed.

    2) Even though early on in my testing I confirmed that the jar file was packaged in the correct fashion, with the Applet.class at the root, later on in my debugging I created a NAnt build script for simplifying the build/sign/deploy process for me. This build script was packaging the jar from a working directory that was not the root of the application. So, the AppletClient.class was not at the root anymore, but nested in sever subdirectories.

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