How is it Possbile to run Groovy class together with java classes using Spring boot

I am trying to run my spring-boot app (using gradle and java) together with groovy classes.

So I added controller (as shown in the examples)

the controller is under src/main/groovy

@RestController
class ThisWillActuallyRun {

    @RequestMapping("/")
    String home() {
        "Hello World!"
    }

}

I also have my java classes under

src/main/java

Iam running spring boot using java -jar (or gradle in dev mode: bootRun)

Code is compiled but the groovy controller isnt loaded.

I miss some concept here about running groovy and java classes side-by-side on the same jar?

Thanks.