Build a RESTful Web Service with Spring Boot

Spring Boot can expose JSON APIs with @RestController and request-mapping annotations.

@RestController
@RequestMapping("/api/users")
class UserController {
    @GetMapping("/{id}")
    ResponseEntity<UserDto> find(@PathVariable long id) {
        return ResponseEntity.ok(service.find(id));
    }

    @PostMapping
    ResponseEntity<UserDto> create(@Valid @RequestBody CreateUserRequest request) {
        UserDto created = service.create(request);
        return ResponseEntity.status(HttpStatus.CREATED).body(created);
    }
}

Use DTOs rather than exposing persistence entities directly. Apply Bean Validation to input and return accurate status codes such as 201, 400, 404, and 409.

Centralize errors with @RestControllerAdvice:

@ExceptionHandler(UserNotFoundException.class)
ResponseEntity<ProblemDetail> handleNotFound(UserNotFoundException ex) {
    return ResponseEntity.of(ProblemDetail.forStatusAndDetail(
        HttpStatus.NOT_FOUND, ex.getMessage())).build();
}

Version public contracts deliberately, document them with OpenAPI, authenticate sensitive operations, limit request sizes, and test serialization and failure responses as carefully as the success path.