Alex,
Thank you for your advice! It makes sense, although I
don't quite understand what's going on...
My current classloader is based on the BCEL example
code. It works fine, except for when the user uses
his own classloader.
Unfortunately, I don't totally understand why they
wrote it that way. And, I don't quite understand why
you wrote your WeavingClassLoader the way you did...
In particular, I don't want to affect where the code
is coming from. In the BCEL example, they write:
protected Class findClass(String className, boolean instrument) {
JavaClass javaClass = Repository.lookupClass(className);
...
javaClass = Debugify.debugifyClass(javaClass, className); // do theinstrumentation
byte[] b = javaClass.getBytes();
clazz = defineClass(className, b, 0, b.length);
return clazz;
}
and you have something very similar:
protected Class findClass(String name) throws ClassNotFoundException {
String path = name.replace('.', '/').concat(".class");
Resource res = new URLClassPath(getURLs()).getResource(path, false);
...
byte[] b = res.getBytes();
byte[] transformed = ClassPreProcessorHelper.defineClass0Pre(this, name,
b, 0, b.length, null);
return defineClass(name, transformed, 0, transformed.length);
}
The bit I'm confused about is the Repository/Resource. Won't
that affect where the class is loaded from? So if the user
writes a weird classloader that just creates a byte array
"magically", our R/R will miss that. (right?)
So shouldn't we be delegating the findClass() stuff to the
existing classloaders? They would then come up with the
byte array and hand that to defineClass(). Our classloaders
would specialize defineClass() to include the instrumentation
and pass the transformed byte array to super.defineClass(),
which would finally turn the byte array into a class.
Does that make sense?
(I've read all I could find on classloaders, but it's still
less then 100% clear.)
================
Looking through your Plug stuff, it looks like you're instrumenting
java.lang.ClassLoader to do instrumentation in all the
define0() methods (yes?). And that's equivalent to what I
said above wrt defineClass()?
================
Finally, does this really work? If a user defines a classloader
which has the bootstrap classloader as parent, will your
enhanced classloader be used?
Sincerely,
-Bil
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