How to write a Java annotation processor?

Question

I may be just looking in the wrong direction but I find the JSE documentation on annotation processing very ... sparse. I want to write an annotation processor which processes annotated String fields and local variables to substitute them with a computed String expression. This should not be too complicated but I'm pretty lost in the Javadoc for javax.annotation.processing.

EDIT: I need to process annotations at compile time because I want to modify the generated code. It should replace annotated constant String expressions with a computed String expression.

Answer 1

This can not be done with a compile time annotation processor. Compile time time annotation processors can only generate new files (and classes) they can not modify existing classes. You can do reflection at runtime but strictly speaking you that is not called annotation processing. Also you won't have access to local variables.

If you're looking on how to write a compile time annotation processor check out https://github.com/pellaton/spring-configuration-validation-processor