Build controllers, DTOs, validation, global error handling, pagination, sorting, and API documentation.
Spring Boot · web
Use the strong answer as your reference, explain it aloud in your own words, then choose how soon you want to review it again.
Interview prompt
Strong answer
A production REST endpoint validates input at the boundary, calls an application service, maps domain outcomes to stable responses, and handles errors consistently. DTOs, pagination, idempotency, and documentation make the contract usable by other teams.
Key points
Interviewer looks for
Walk through one endpoint, including invalid input, missing data, authorization failure, database failure, and a successful response.
Java example
1@PostMapping
2ResponseEntity<OrderResponse> create(@Valid @RequestBody CreateOrderRequest request) {
3 return ResponseEntity.status(HttpStatus.CREATED)
4 .body(mapper.toResponse(service.create(request)));
5}Topic interview questions
These questions are tied to this lesson. Read each question aloud, then compare your explanation with the strong answer.
Strong answer
It asks the validation provider to check constraints on the bound request object before the controller method proceeds. The API should translate failures into a stable field-level error response.
Strong answer
Use a consistent error representation and a centralized exception handler to map validation, domain, authorization, and unexpected failures to appropriate status codes. Do not leak stack traces or database details.
Strong answer
Separate DTOs prevent persistence changes from silently changing the public contract, limit fields returned to clients, and make request validation explicit. Mapping is an intentional boundary rather than accidental serialization.
Strong answer
Accept an idempotency key or use a client-provided unique identifier, persist the result of the first successful attempt, and return the same outcome for retries. This prevents duplicate orders or payments.
Strong answer
Document request and response schemas, validation rules, authentication, status codes, error shapes, pagination, sorting, rate limits, and idempotency behavior. Examples should cover both success and failure paths.
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