cglib - Byte Code Generation Library

cglib - Byte Code Generation Library is high level API to generate and transform Java byte code. It is used by AOP, testing, data access frameworks to generate dynamic proxy objects and intercept field access.

https://github.com/cglib/cglib/wiki

Here is good example for this:

http://markbramnik.blogspot.kr/2010/04/cglib-introduction.html

In addition, I attached sample project to be able to run his explanation:

CglibTest.zip

TODO: I need to investigate and study cglib's usage more!

It's now widely used at famous frameworks like Hibernate, Spring and more.