Introduce argument resolver for OffsetScrollPosition

[quaff]

Just like org.springframework.data.web.PageableHandlerMethodArgumentResolver did for Pageable

[mp911de]

We do not have a good way to capture the keyset type. For offset-based positions, we could provide something. Feel free to submit a pull request. We should provide argument resolves for the servlet- and the reactive stack.

[quaff]

I will try OffsetScrollPosition first.

[quaff]

For KeysetScrollPosition:

Given

@GetMapping("/users")
public Window<User> scroll(@SortDefault(sort = "id", direction = ASC) Sort sort,
		@RequestParam(defaultValue = "10") int limit, KeysetScrollPosition position) {
	Specification<User> spec = (root, query, cb) -> null;
	return this.userRepository.findBy(spec, q -> q.limit(limit).sortBy(sort).scroll(position));
}

Use implicit id as sort:

/users -> ScrollPosition.forward(Map.of())
/users?id=10 -> ScrollPosition.forward(Map.of("id", 10))
/users?direction=backward -> ScrollPosition.backward(Map.of())
/users?direction=backward&id=10 -> ScrollPosition.backward(Map.of("id", 10))

Use explicit username as sort:

/users?sort=username -> ScrollPosition.forward(Map.of())
/users?sort=username&username=test -> ScrollPosition.forward(Map.of("username", "test"))
/users?sort=username&direction=backward -> ScrollPosition.backward(Map.of())
/users?sort=username&direction=backward&username=test -> ScrollPosition.backward(Map.of("username", "test"))

Use explicit foo and bar combination as sort:

/users?sort=foo,bar -> ScrollPosition.forward(Map.of())
/users?sort=foo,bar&foo=foo&bar=bar -> ScrollPosition.forward(Map.of("foo", "foo", "bar", "bar"))
/users?sort=foo,bar&direction=backward -> ScrollPosition.backward(Map.of())
/users?sort=foo,bar&direction=backward&foo=foo&bar=bar -> ScrollPosition.backward(Map.of("foo", "foo", "bar", "bar"))

The key problem is how to convert keys to correct type, maybe we should introduce an annotation to extract actual type from underlying domain object, for example

@TypeHints(from = User.class) KeysetScrollPosition position

WDYT? @mp911de