Error handling is part of an API contract. When every endpoint returns a different error format, clients need special logic for each failure. Spring Boot can provide one predictable structure for validation, missing resources, conflicts, and unexpected errors.
Create domain-specific exceptions
Use meaningful exceptions such as ResourceNotFoundException, ReservationConflictException, or AccessDeniedException. These names describe the business problem and keep service methods readable. Avoid throwing a generic runtime exception for every case.
Centralize translation to HTTP
A class annotated with RestControllerAdvice can catch exceptions and convert them into ResponseEntity objects. This keeps controllers focused on successful request handling while one component controls status codes and response fields.
Return useful but safe details
A practical error response can include a timestamp, status, error code, message, request path, and field validation details. Do not expose stack traces, SQL statements, or internal infrastructure information to public clients.
Separate expected and unexpected failures
A missing record may produce 404, invalid input 400, and a booking conflict 409. An unhandled technical failure should usually become 500 and be logged with enough context for investigation. The public message can remain safe while internal logs contain diagnostic detail.
Test the error contract
Integration tests should verify both the status code and response body. Consistent error handling improves frontend development, monitoring, support, and debugging. It turns failures from random surprises into a documented part of the system.