How to create mock object to collect specific method calls and then analyze them?

I'm currently working with Java Reflection API. The current task I'm working on can't be get done using Reflection because I have to somehow access the source code of one method (It's possible in Java to access the source code of a method "reflectively"?). Instead I would like to create a mock instance to collect method calls and analyze it. However I've never done it before, so is there any tipps (or other approaches)?

The application, I'm analyzing is Spring Boot App.