Generate Expert Spring Boot Controllers

This skill embodies a Spring Boot controller expert covering REST API design, HTTP semantics, validation, error handling, and production practices. Core RESTful design guidance covers using HTTP methods with their proper semantic meaning, designing resource-oriented URLs that represent entities rather than actions, returning appropriate status codes (200, 201, 204, 400, 404, 409, 500), and keeping response structures consistent across endpoints. A full UserController example demonstrates the pattern: a @RestController with @RequestMapping, @Validated, and @Slf4j, constructor-injected service dependency, a paginated GET list endpoint using Pageable, a GET by ID endpoint, a POST create endpoint that returns 201 Created with a Location header built via ServletUriComponentsBuilder, a PUT update endpoint, and a DELETE endpoint returning 204 No Content.

Validation is handled through Bean Validation annotations on request DTOs - @NotBlank, @Size, @Email, @NotNull, @Min/@Max, and nested @Valid for embedded objects like an address - each with a custom error message. A @RestControllerAdvice-based GlobalExceptionHandler centralizes error handling, converting MethodArgumentNotValidException into a structured ErrorResponse with field-level validation details and a 400 status, and ResourceNotFoundException into a 404 response.

Advanced patterns cover content negotiation and API versioning (producing both JSON and XML, reading an Accept-Version header), asynchronous processing for long-running operations (a bulk-import endpoint that generates a task ID, kicks off work via CompletableFuture.supplyAsync, and immediately returns 202 Accepted with a task-status response), method-level security via @PreAuthorize expressions (including a delete endpoint that blocks a user from deleting their own account via #id != authentication.principal.id), and response caching with @Cacheable/@CacheEvict plus HTTP Cache-Control headers.

Testing guidance shows @WebMvcTest with MockMvc and a mocked service layer, asserting on status codes, response headers, and JSON body fields for both success and validation-failure cases. Documentation guidance shows OpenAPI/Swagger annotations (@Tag, @Operation, @ApiResponse, @Parameter) for self-documenting endpoints.

Use this when designing or reviewing Spring Boot REST controllers and needing concrete, idiomatic patterns for CRUD endpoints, validation, centralized error handling, security annotations, caching, or test coverage. The skill's closing guidance is explicit about priorities: keep controllers thin by delegating business logic to service layers, use DTOs for data transfer rather than exposing entities directly, implement comprehensive validation, provide meaningful error responses, and maintain proper HTTP semantics throughout.

Inputs are the API's resource model and business requirements; output is a set of controller, DTO, validation, and exception-handling classes following Spring Boot conventions. A representative delete endpoint:

@DeleteMapping("/{id}")
public ResponseEntity<Void> deleteUser(@PathVariable Long id) {
    userService.deleteUser(id);
    return ResponseEntity.noContent().build();
}

Built on Spring Boot's web MVC stack (@RestController, @RequestMapping), Bean Validation, Spring Security's @PreAuthorize, Spring's caching abstraction (@Cacheable/@CacheEvict), MockMvc for testing, and OpenAPI/Swagger annotations for API documentation.

Java/Spring Boot developers designing or reviewing REST API controllers who want idiomatic, production-grade patterns for CRUD design, validation, error handling, security, caching, and testing rather than assembling these individually from documentation.