Yeah, if I wouldn't care for type safety, and I'd want to write validation code for stuff currently handled by GSON instead of me, by the class definitions.

We use Groovy for some things, but here I'd stick to Java.

Also Groovy has limited IDE support.

Apache Groovy's dynamic typing, closures, and shorthand collection syntax (from v. 1.0) are great for testing and playing with Java classes, and I'm told Groovy's Ruby-like MOP is useful for Grails developers, but the stuff added later (like generics in v. 1.5) made the language klunky and overdone. Best switch to Java (or Scala/Kotlin/etc) once you need anything to be typed, let alone with generics.