How to replace class name in .class file code?

Question

Java

Good afternoon.
Suppose I have a class .class file with the name com.example1.FooFoo.
Now I want this file to be loaded as the com.example1.Bar class.
In other words, write a ClassLoader that:
1. Received a request from the application to load the com.example1.Bar class.
2. In some way that doesn't matter now, I determined that I needed to load the code from the com/example1/FooFoo.class file.
3. Loaded bytecode from file com/example1/FooFoo.class (which compiled as class FooFoo)
4. Replaced FooFoo class name in bytecode with Bar
5. Called defineClass

Answer 1

Here, I think, you need to write (or find) JavaAgent .
May I ask - what is it for?