Chapter 144: Pagination in Java

Pagination splits large result sets into pages so HTTP responses stay fast and bounded. Offset pagination (?page=3&size=20) is easy but degrades on deep pages; keyset (seek) pagination uses WHERE id > ? ORDER BY id LIMIT ? and a cursor—stable under concurrent inserts when keys are monotonic.

1. Topic title

Pagination: cap response size; choose offset or keyset based on data churn and depth

2. What it means

Page<T> in Spring Data wraps content, totalElements, number, size—count(*) queries cost money on big tables.

Keyset needs a unique sort key—composite cursors when sorting by non-unique columns (tie-breaker id).

Opaque cursors (Base64 JSON) hide internal ids if needed.

3. Why it is used

Mobile feeds and admin tables both need predictable latency.

Database planners prefer range scans over large offsets.

4. Mental sketch

Offset pagination is flipping to page 400 of a magazine while someone reorders pages—you skip wrong. Keyset is “start after this bookmark”—robust when the book grows.

5. Java code example

import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;
 
/** Illustrative service API — repository returns Page<ItemEntity>. */
public final class PageSketch {
    private PageSketch() {
    }
 
    public static Pageable firstPage(int size) {
        return PageRequest.of(0, Math.min(size, 100));
    }
}

Clamp size server-side—clients lie.

6. Explanation of code

PageRequest.of(page, size) is zero-based page index—document that for frontend teams.

7. Common mistakes

Unbounded size=999999—OOM or timeouts.

Sorting without stable tie-breaker—duplicate/missing rows across pages.

8. Best practices

Return Link headers (RFC 8288) for next/prev when easy—clients follow URLs you control.

Keyset for infinite scroll; offset for jump to page UIs with full counts when acceptable.

9. Small practice task

Implement GET /items?afterId=42&limit=20 with repository query findByIdGreaterThanOrderById—compare explain plans vs OFFSET 10000.

Beginner tip

“Total pages” UI forces COUNT(*)—if that query times out, switch UX to “has next” only.