Implement a JAX-RS REST client to batch queries

I am looking for a freelancer to extend a JAX-RS REST client with mapped json to java classes with JAX-RS annotations. The ideal candidate should have experience with the JAX-RS standard and spring-boot.
The API to use is https://aebb.es/xh6bj your task will be to implement the Batches API with polling for finishing the posted batches

Use common spring boot pattern:
- service class(es) to access API
- DTO classes

In later phase MSx this classes will be persisted into postgresql+h2

Deliveries?
- in our on premise git (access will be granted to you)
- full sources
- maven
- JDK 17

Payment?
- you estimate in a WBS after getting the task
- we discuss about clearances and effort
- we mutually agree to effort
- we assign you the task after agree
- you implement & delivery
- we pay
(basically the rules of freelancer)

Closed book vs open book?
We work only on open book.
Closed book means you are unwilling to define a WBS for the work and you add only a price tag to the task. We are sorry we will not hire you in such a case!