How to load modified superclass in Java?

Question

• I have a class A that extends B.
• I created a CustomClassLoader that extends ClassLoader for use defineClass(className, byte[], offset, length).
• I have installed new CustomClassLoader(Thread.currentThread().getContextClassLoader()). So the parent of my CustomClassLoader is the ClassLoader from the current thread.
• I modified class B using the ASM structure. I wrote my modified class in a .class file and use a decompiler to make sure it works. And it works.
• I added a modified class B to my CustomClassLoader
• I installed Thread.currentThread().setContextClassLoader()using my CustomClassLoader.
• I load A using Class.forName(String, true, the CustomClassLoader).
• But the loaded class B seems to be the original class.

What did I misunderstand? If you need more information, a detailed topic is on my GitHub .

Answer 1

Java class loaders first look for the parent class loader before looking in it.

The loadClass method in ClassLoader performs these tasks so that when called to load the class:

• If the class is already loaded, it returns it.
• Otherwise, it delegates the search for the new class to the parent class loader.
• If the loader of the parent class does not find the class, loadClass calls the findClass method to find and load the class.

( Understanding Extension Class Loading - Oracle)

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Answer 2

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