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Spring Boot 4 Microservices & REST APIs · Lesson

Dynamic Queries with Specifications

Build flexible queries programmatically.

Dynamic Queries with Specifications is a free Spring Boot 4 Microservices & REST APIs lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Spring Boot 4 Microservices & REST APIs learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

The Problem with Static Queries

When users can filter by many optional fields, writing one query method per combination explodes quickly.

Spring Data Specifications let you build queries dynamically at runtime based on which filters are present.

JpaSpecificationExecutor

Extend JpaSpecificationExecutor on your repository to enable Specification-based queries.

public interface UserRepository
    extends JpaRepository<User, Long>,
            JpaSpecificationExecutor<User> {
}

A Specification

A Specification<T> describes a single WHERE predicate using the JPA Criteria API.

Specification<User> hasName(String name) {
    return (root, query, cb) ->
        cb.equal(root.get("name"), name);
}

Executing a Specification

Pass the spec to findAll.

List<User> users =
    userRepository.findAll(hasName("Alice"));

Combining with and

Specifications compose with and, or, and not.

Specification<User> spec =
    hasName("Alice").and(isActive(true));
List<User> users = userRepository.findAll(spec);

Building Conditionally

The real power: add predicates only when the filter is supplied.

Specification<User> spec = Specification.where(null);
if (name != null) {
    spec = spec.and(hasName(name));
}
if (active != null) {
    spec = spec.and(isActive(active));
}
return userRepository.findAll(spec);

Like and Comparison Predicates

The Criteria builder offers many predicate types.

Specification<User> nameLike(String part) {
    return (root, query, cb) ->
        cb.like(root.get("name"), "%" + part + "%");
}

Specification<User> olderThan(int age) {
    return (root, query, cb) ->
        cb.greaterThan(root.get("age"), age);
}

Joining Related Entities

Specifications can navigate joins to filter on associated entities.

Specification<User> inCity(String city) {
    return (root, query, cb) ->
        cb.equal(root.join("address").get("city"), city);
}

Specifications with Paging

Combine a Specification with a Pageable for filtered, paginated results.

Page<User> page = userRepository.findAll(
    spec, PageRequest.of(0, 20));

Counting Matches

count accepts a Specification too.

long matches = userRepository.count(hasName("Alice"));

Reusing Predicate Factories

Group spec factories in a helper class so they can be reused and unit tested.

public class UserSpecs {
    public static Specification<User> active() {
        return (root, q, cb) ->
            cb.isTrue(root.get("active"));
    }
}

Quick Check

Test your understanding of Specifications.

Recap

You learned dynamic querying:

  • Extend JpaSpecificationExecutor
  • A Specification is one Criteria predicate
  • Compose with and/or, add conditionally
  • Combine with Pageable for filtered pages

Frequently asked questions

Is the “Dynamic Queries with Specifications” lesson free?

Yes — the full text of “Dynamic Queries with Specifications” is free to read here on the web, and the Spring Boot 4 Microservices & REST APIs course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Spring Boot 4 Microservices & REST APIs course, upgrade to CoddyKit PRO.

What will I learn in “Dynamic Queries with Specifications”?

Build flexible queries programmatically. You practise Spring Boot 4 Microservices & REST APIs with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Spring Boot 4 Microservices & REST APIs?

No prior experience is required. Spring Boot 4 Microservices & REST APIs on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Dynamic Queries with Specifications” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Spring Boot 4 Microservices & REST APIs lesson?

Yes. Every Spring Boot 4 Microservices & REST APIs lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Dynamic Queries with Specifications
  2. Projections and DTOs
  3. Auditing with @CreatedDate
  4. Pagination and Sorting
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