Question

Class clazz = ...;
InputStream is = ClassLoader.getSystemResourceAsStream(clazz.getName().replace('.', '/') + ".class");

The input stream is returning null. I have used a simple java instrumentation agent to log classes as they are loaded and the class (clazz) is definitely being loaded by the ClassLoader. I’ve also tried

... Thread.currentThread().getContextClassLoader().getResourceAsStream(...));

and it returns null as well. What would be some possible causes for the resource not being able to be found by the class loader?

Answer 1

The Class has apparently been loaded by a different ClassLoader than the ones you’re trying to find it with. Try this instead:

InputStream is = clazz.getClassLoader().getResourceAsStream(
    clazz.getName().replace('.', '/') + ".class");

Short of a flaw in the JVM, I don’t think that can possibly return null.