Module 17: Spring Boot Service Development
Mini-Project: Task Management API
Assemble a task management API that feels like a professional service, not a disconnected framework demo. You will combine controllers, validation, services, repositories, DTOs, configuration, and tests into one small but coherent backend application.
Author
Java Learner Editorial Team
Reviewer
Technical review by Java Learner
Last reviewed
2026-04-17
Java version
Java 25 LTS
Learning goals
- Turn Spring concepts into one layered, end-to-end service
- Practice package structure, validation flow, persistence, and error handling together
- Produce a mini-project that is easy to demo, test, and extend
Before you start
- You understand classes, objects, exceptions, collections, and basic persistence concepts
Lesson roadmap: Start with the mental model, then follow the design choices, common pitfalls, and the practical workflow you should apply in a real project.
Project goal: Build a task API with endpoints for creating, listing, updating, and completing tasks.
What to practice: Controller-to-service flow, DTO mapping, validation, persistence, and exception-to-response handling.
Suggested layers: Controller for HTTP, service for business logic, repository for persistence, DTOs for boundary models.
Success check: The project should feel maintainable when someone adds one more endpoint or validation rule later.
Project scope: Support creating tasks, listing tasks, updating title or status, and marking tasks complete. Keep the first version intentionally small so the architecture stays visible.
Suggested package plan: api for controllers and DTOs, service for business logic, repository for data access, domain for entities, and config for application configuration.
Milestone plan: Start with one read endpoint and one create endpoint, add persistence, add validation, add update paths, then add exception handling and tests. This order produces a working slice early.
Professional finish: Include sample requests, a short README, configuration instructions, and one integration or slice test that proves the API boundary works.
How to study this module: Keep one small service running while you learn. Seeing one controller call one service and one repository is much easier than reading isolated annotations with no end-to-end flow.
Code review mindset: Spring code stays healthy when each layer has one job. Controllers translate HTTP, services coordinate rules, repositories load and save data, and configuration wires the environment together.
Production habit: Favor explicit boundaries over framework magic. Auto-configuration is helpful, but teams still need to know where behavior comes from and how to override it safely.
Runnable examples
A service boundary keeps business logic out of the controller
@Service
class TaskService {
public TaskDto createTask(CreateTaskRequest request) {
return new TaskDto(1L, request.title());
}
}Expected output
The controller can delegate business logic instead of owning it directly.
A service method can coordinate repository work and DTO mapping
@Service
class TaskService {
TaskDto complete(long id) {
Task task = repository.findById(id).orElseThrow();
task.markCompleted();
return mapper.toDto(repository.save(task));
}
}Expected output
Business logic stays in the service layer while the controller remains a thin HTTP adapter.
Common mistakes
Adding too many framework features before the core task flow even works
Finish a thin vertical slice first, then add extras such as pagination, security, or documentation.
Leaving package structure and naming vague because the project is “small”
Mini-projects are exactly where strong structure habits should be practiced.
Mini exercise
Write the package structure and first three endpoints for the task API before coding. Then list which class will own validation, which class will own persistence, and which class will own HTTP response shaping.
Summary
- The mini-project ties Spring Boot pieces together into one service.
- Thin controllers and clear service boundaries keep the design maintainable.
- This is the transition from framework concepts to full backend application work.
- A strong Spring mini-project demonstrates boundaries, not just annotations.
- Shipping one clean vertical slice is better than sketching many half-finished features.
Next step
The next module turns from framework design to the delivery workflow that makes services safe to change and easy to ship.
Sources used