service-layer-extractor

Refactoring controllers into a service layer involves moving business logic into injectable services, establishing clear routes → controllers → services → repositories boundaries, and wiring units with dependency injection to enable isolated unit testing.

Separating business logic from route handlers requires introducing a service layer where services encapsulate core rules and data orchestration, allowing controllers to focus solely on HTTP concerns while services handle the underlying business operations.

A migration to dependency injection follows a phased rollout plan: create service classes, connect them to existing controllers, introduce repositories for data access, and validate each phase with unit tests to preserve public APIs.

You need a service layer when business logic accumulates in route handlers, making them difficult to test and maintain; extracting services enforces clear boundaries and allows mocking data access for isolated unit testing.

Yes, introducing a service layer preserves existing public APIs by wiring services and injection points internally, allowing controllers to delegate orchestration to services while maintaining their original HTTP interface contracts.

Moving business logic to services improves unit testing by isolating core rules from the HTTP layer, allowing you to mock repositories and dependency injection points to test business orchestration independently of web infrastructure.