Pagination

Introduction

Returning 100,000 rows in one API call will crash your app and your database. Spring Data's Pageable interface provides standard offset/limit pagination with sorting — essential for every list endpoint.

Informative example

Paginated REST endpoint:

@GetMapping("/products")
public Page<ProductDto> list(
    @RequestParam(defaultValue = "0") int page,
    @RequestParam(defaultValue = "20") int size,
    @RequestParam(defaultValue = "name,asc") String[] sort
) {
    Pageable pageable = PageRequest.of(page, size, Sort.by(parseSort(sort)));
    return productRepo.findAll(pageable).map(ProductDto::from);
}

// Repository
Page<Product> findByCategory(String category, Pageable pageable);

// Response includes: content, totalElements, totalPages, number, size

Best practices

• Cap max page size (e.g. 100) to prevent abuse.
• For deep pagination (page 10,000+), use keyset/cursor pagination instead of offset.
• Return total count only when the UI needs it — it's expensive on large tables.

Purpose of this lesson

Master Pagination so you can apply it confidently in production Java code, technical interviews, and code reviews.

Step-by-step explanation

1. Understand the core idea behind Pagination.
2. Walk through the runnable example and tweak it in the playground.
3. Apply the pattern in a small Spring Boot or CLI exercise of your own.
4. Re-read the common mistakes and interview Q&A to lock the concept in.

Interactive workflow diagram

Debugging tips

• Read the full stack trace — Java's exception messages name the offending class and line.
• Reproduce in the smallest possible main() method before fixing in the real app.
• Use IntelliJ's debugger breakpoints and 'Evaluate Expression' rather than scattering System.out.

Optimization strategies

• Keyset pagination: WHERE id > :cursor ORDER BY id LIMIT 20 — O(1) vs OFFSET which scans skipped rows.

Enterprise example

Teams at Netflix, Uber and Goldman Sachs apply Pagination daily — usually wrapped behind Spring Boot services with observability hooks (Micrometer + OpenTelemetry).

Interview questions & answers

Summary

In this lesson you learned Pagination — the concept, syntax, a runnable example, and the production pitfalls to avoid. Apply it in the playground before moving on.