java applet ClassNotFoundException with codebase

I'm starting to work on an applet that will replace an existing one. Having never developed an applet before, I thought I'd get going with the popular HelloWorld example. I am able to run it a couple different ways: in the appletviewer, and also in a browser if I put the JAR file containing the HelloWorld class in the same directory as the HTML (i.e. http://localhost:8080/myApp). I also got it to work when I put the JAR in a directory called HelloWorld just below the myApp directory and specified the codebase parameter in the <applet> tag as HelloWorld. But when I try to specify WEB-INF directories such as classes or lib, I get a ClassNotFoundException. What am I doing wrong?

But when I try to specify WEB-INF directories such as classes or lib, I get a ClassNotFoundException. What am I doing wrong?

Those directories are only meant for classes/jars that are used in JSP and servlets (i.e. the stuff the server needs). The resources inside them are available to site visitors. In this sense 'visitor' means a User Agent (i.e. a browser) or a client side plug-in (such as Flash or the JRE).

You can confirm this for yourself by pasting the full URL to the Jar in the web browser address bar and hit 'enter' to browser to it. The server will give a message back to the effect 'forbidden'.

See also the WEB-INF info. page which expands:

WEB-INF is the name of a folder found in Java web applications. It is used to store deployment information such as the web.xml, required library files and compiled class files. It is normally not accessible from web. Any files which you want to put on war but do not want to make to public then web-inf is the place where you can keep those files.