There's total mess with GraphQL and Java (Spring). There are multiple projects, and multiple examples, but totally inconsistent.
What I understand Spring Boot should gives is OOTB working solution, and (to some extent) it works like this. Project which gives you such experience is on Github https://github.com/graphql-java-kickstart. Especially https://github.com/graphql-java-kickstart/graphql-spring-boot gives you possibility to create schema, make resolver and everything else is done automatically.
Problem is when you try to replace resolver - which seems like very simply datafetcher - with custom datafetcher. As I know there's no possibility to make asynchronous resolver, or batched resolver - you have to make datafetcher.
To make custom datafetchers one needs to make custom wiring etc, replacing spring-boot solution, or using it somehow (how?). There's no single point of true, how to do that properly. I even found that BatchedDataFetcher are deprecated(!) before they even get a good Spring Boot support/example (see: GraphQL Java: Using @Batched DataFetcher)
Because of that I even don't know where to look for solution. What I would welcome to see is to have an example which has:
- Spring Boot support
- asynchronous/parallel datafetcher
- batched datafetcher
- connecting multiple services with GraphQL endpoints (maybe out of scope)
- paging/filtering