Custom applet class loader, how?

Question

Fellow Java programmers;
I would like to load 'secure' class files (ie encrypted) into an applet at startup time.
I have code that does this for a normal java program.
How do you go about using a custom class loader in an applet?
Would something like this work? (using say *.Xclass local encrypted class files)
..somewhere in theapplet: init().. runClass()
.public void runClass(name)
{ aCL = new AppletClassLoader(); // extends ClassLoader
Class c = aCL.loadClass(name);
Method m= c.getMethod("main"..)
m.invoke(...);
Your comments or pehaps a code snippet would be appreciated.
Thanks, John

Answer 1

John,
this does not work without modifying the runtime client environment.
Security constraints will prevent you from setting up a new class loader, so you will have to at least grant this permission in a policy file deployed to your clients as you will have to deplay the encryption keys.
As bringing in a new class loader from an applet is highly security critical, this should be backed by a rather strict policy and by signing the applet.
Though the example you provided might work, the class loader implementation itself is not so easy-
If you would like to imitate the findClass() and loadClass() methods from SUN you will see that those are complex and not suitable for "hooking" in an encrypted stream.
You might try an easier way:
Load the class data as an encrypted byte array, decrypt it and use SUNs class loader methods to define a JAVA class out of this byte array:
ClassLoader.defineClass(String�name, byte[]�b, int off, int�len)
This seems to be easier than implmenting your own loader.
Oliver