code: @Override
      public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
              ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
  
          ClassReader cr = new ClassReader(classfileBuffer);
          ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_FRAMES);
          ClassVisitor cv = new ClassAdapter(cw);
          cr.accept(cv, ClassReader.SKIP_FRAMES);
          return cw.toByteArray();
      }
docs: /*
  Called during class loading.
  
  Use ASM to modify class bytecode if necessary using the ClassAdaptor