Single order lookup API

Complete an API built on Spring Boot 3 and JPA (in-memory H2) that finds a single order by id and returns it. Looking up a stored order responds with 200 and a body (items and quantities).

An API that looks up a single resource by id is mainly about the flow where the controller and service split roles to receive the lookup result and send it out as a response. This problem completes a single lookup that finds one order by id and returns it with 200 and its body (items and quantities), and verifies in real code that a normal lookup returns the order.

In Spring, where do lookup logic and the HTTP response get split?

The controller handles only the HTTP boundary, while business rules such as the lookup live in the service. The controller sends out as a response what the service found.

How do you verify a single-item lookup API?

Look up a stored order by id and confirm that the 200 response and its body (items and quantities) come back as that order.