Hi Walter,
Just checked the GitHub source and wow, it's been quite a long while since I've seen a pure Java / Ant project! Reminds me of Ardor, a Java blockchain project in active development that doesn't use Maven or Gradle.
Anyway, I'm a Java architect/developer with over 18 years of experience, mostly with Java EE and Spring/Spring Boot and its frameworks: JHipster, CUBA Platform, and Grails. I also have over four years experience with Groovy/Grails and Kotlin, including Grails GORM.
In the past few months I have also been using/studying Vert.x, RxJava 2, GraalVM, Micronaut, and Quarkus, with particular interest with reactive streams and server-push events. Server-side reactive streams could be used with your project such as v2.0+ of JAX-RS which supports it (although it requires Java 8+ I think).
Also have excellent experience with API-first development with Swagger/OpenAPI.
Highly interested with your project. Thank you.