如何使用ASM重命名类并保留在同一类加载器中？

Question

I'm trying to rename a class using ASM 4.0 :

ClassReader reader = new ClassReader(
    loader.getResourceAsStream("test/MyClass.class")
);
ClassWriter writer = new ClassWriter(reader, 0);
ClassVisitor visitor = new RemappingClassAdapter(visitor, new Remapper() { /* skipped */ });
reader.accept(visitor, 0);
return new ClassLoader() {
    public Class<?> load(final String name, final byte[] bytes) {
        return this.defineClass(name, bytes, 0, bytes.length);
    }
}.load("test/MyClass", writer.toByteArray());

I skipped the renaming part intentionally. A new class should be an exact copy of the original one. It is, but it can't be used any more as an old one:

java.lang.ClassCastException: test.MyClass cannot be cast to test.MyClass

How to stay in the same class loader?

Answer 1

In the JVM, each class is identified by it's fully qualified name AND the class loader which loaded the class. This explains your ClassCastException.

Once you rename the class, you should be able to load your renamed class in any classloader. Use reflection to get hold of the "ClassLoader.defineClass()" method and use it to call it on getClass().getClassLoader();

Method m=ClassLoader.class.getDeclaredMethod("defineClass",
 String.class,byte[].class,int.class,int.class) 
m.setAccessible(true);
m.invoke(getClass().getClassLoader(), ... )