Spring JPA data: filtering page content results in a smaller page than requested

Question

Situation

We create a simple API to get the bars belonging to this Foo using pagination, for example:

GET /foo/1/bar?pageSize=50&pageOffset=1

The backend uses Spring support for paganizing JPA data, for example:

Page<Bar> barsPage = repo.findBarsForFoo(fooId, new PageRequest(pageOffset, pageSize));

Problem

We need to filter out certain elements from barPage - easily, for example:

List<Bar> filtered = barsFilter.removeSome(barsPage.getContent())

Filtering component delegates to other services (let them refuse them):

class BarsFilter {
  @Autowired Rejector1 rejector1;
  @Autowired Rejector2 rejector2;

  public List<Bar> filterSome(List<Bar> bars) {
    return bars.stream()
      .filter(bar -> rejector1.matches(bar))
      .filter(bar -> rejector2.matches(bar))
      .collect(toList());
  }
}

The problem is that the API client will receive fewer elements than they requested.

Gotchas

The filtering logic is complex and depends on other components. It cannot be written as a single database query.

? ? ? Spring Data JPA ?

Answer 1

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