Introduce a new scrolling-based ItemReader

[scordio]

Spring Data Commons 3.1 introduced the concept of scrolling (spring-projects/spring-data-commons#2787) and I'm particularly interested in scrolling using keyset-filtering, which provides performance benefits with large datasets.

It would be nice to have an item reader compatible with this concept.

As far as I can judge, RepositoryItemReader is highly coupled with PagingAndSortingRepository, therefore an extension doesn't seem to be the right direction as scrolling is supposed to work with any Repository.

Therefore, my proposal would be to introduce a new ItemReader, maybe a ScrollingRepositoryItemReader?

Happy to work on a PR in case the idea is accepted.

My concrete use case: in several Batch & JPA-based projects that are still on Spring Boot 2.7, scrolling based on keyset-filtering is currently achieved via a custom AbstractPaginatedItemReader with an underlying Spring Data JPA repository using QueryDSL predicates. After upgrading to Spring Boot 3, the QueryDSL predicates will be replaced by the Spring Data scrolling API. I would also be very happy to throw away the custom item reader if Spring Batch offered an idiomatic way to achieve the same result.

[scordio]

I'm reconsidering my previous suggestion to add a new ScrollingRepositoryItemReader.

Maybe there is a way to generalize RepositoryItemReader and make it work with the new scrolling patterns, without breaking existing code. I have a few new setters in mind, paired with an overall check in afterPropertiesSet to verify that the reader is configured for either the current behavior or the scrolling one.

I'll look into it and try to come up with a proposal.