API / Apache Grails Interview questions
What is the difference between a Grails controller and a Grails service?
Both are Groovy classes managed by Grails' conventions, but they sit at different layers of the application and are responsible for fundamentally different concerns.
| Controller | Service |
| Location: grails-app/controllers | Location: grails-app/services |
| Handles HTTP requests, params binding, rendering views/JSON | Holds business logic, coordinates persistence and external calls |
| Not transactional by default | Transactional by default for every public method |
| URL-addressable, reached directly by a browser or API client | Not URL-addressable; called internally by controllers or other services |
The intended flow is that a controller receives a request, delegates the real work to one or more services, and then renders whatever result the service returns — keeping the controller's own logic limited to request/response concerns and letting the service layer hold logic that's easy to test and reuse independent of any particular HTTP endpoint.
Which of the two is transactional by default for every public method?
Which of the two is directly URL-addressable by a browser or API client?
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