Java write Code that is just run at compile time?

Question

is it possible to write a "maven plugin" or something like that which changes the .java at compile time?

For example:

@Entity
... class ... {
  @Id
  long id
}

I would like to comment out all the Annotations and Create a ORM-Mapping.xml / Persistence according to the entitys

If you have already the JPA annotation why not using them instead of going back to xml based mapping? Or what is the real problem here? — khmarbaise, Oct 01 '18 at 08:46
@prosp so ... the code isn't even compiling yet and you want it to run? — Stultuske, Oct 01 '18 at 08:51
This seems to be an A-B- question. There may be a better/easier way to achieve what you want to do (some deploy-time configuration of the database?) without a source code pre-processor or compile-time macro (both of which are not well established in Java). — Thilo, Oct 01 '18 at 10:06

score 0 · Answer 1 · answered Oct 01 '18 at 08:34

The annotations are mostly based on the configuration files which enable/disable their recognition.

Use the Spring profiles to distinguish the configuration classes. If the special profile will appear, no configuration classes will be recognized. The solution requires to make all the configurations configurable according to the Spring profiles.

@Configuration
@Profile("noAnnotations")
public class SomeConfigurationClass

score 0 · Answer 2 · answered Oct 01 '18 at 21:19

It's possible. Project lombok modifies compiled code however there's no exposed API to do that. (See How does lombok work?) Which is what you want if you have to strip annotations. Disabling all annotations at runtime is probably not reasonable. If you just want to generate something from annotations found in compiled classes that is much simpler

score -1 · Answer 3 · answered Oct 01 '18 at 08:54

What you describe sounds like you're looking for something like a C/C++ preprocessor/templating - feature?

Maybe Annotation Processing can help you https://docs.oracle.com/javase/8/docs/api/javax/annotation/processing/Processor.html

Apart from that - inferring a persistence.xml from your entities annotations is something the Spring Framework does.

Java write Code that is just run at compile time?

3 Answers3