java 45 lines · 9 steps

Bean Validation in a Spring REST controller

A Spring controller validates request bodies with annotations and turns validation failures into structured 400 responses.

Explained by highlit

Spring Intermediate validation rest-api exception-handling dependency-injection dtos

1@RestController
2@RequestMapping("/api/users")
3public class UserController {
4 
5    private final UserService userService;
6 
7    public UserController(UserService userService) {
8        this.userService = userService;
9    }
10 
11    @PostMapping
12    public ResponseEntity<UserResponse> create(@Valid @RequestBody CreateUserRequest request) {
13        User user = userService.register(request);
14        return ResponseEntity.status(HttpStatus.CREATED).body(UserResponse.from(user));
15    }
16}
17 
18public record CreateUserRequest(
19        @NotBlank(message = "name is required")
20        String name,
21 
22        @Email(message = "must be a valid email address")
23        @NotBlank(message = "email is required")
24        String email,
25 
26        @Size(min = 8, message = "password must be at least 8 characters")
27        String password
28) {}
29 
30@RestControllerAdvice
31public class ValidationExceptionHandler {
32 
33    @ExceptionHandler(MethodArgumentNotValidException.class)
34    @ResponseStatus(HttpStatus.BAD_REQUEST)
35    public ValidationErrorResponse handleValidation(MethodArgumentNotValidException ex) {
36        List<FieldErrorDetail> errors = ex.getBindingResult().getFieldErrors().stream()
37                .map(err -> new FieldErrorDetail(err.getField(), err.getDefaultMessage()))
38                .toList();
39        return new ValidationErrorResponse("Validation failed", Instant.now(), errors);
40    }
41 
42    public record ValidationErrorResponse(String message, Instant timestamp, List<FieldErrorDetail> errors) {}
43 
44    public record FieldErrorDetail(String field, String message) {}
45}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Pairing @Valid with @RequestBody makes Spring enforce Bean Validation constraints before your handler runs.
2A @RestControllerAdvice centralizes error formatting so every controller returns consistent failure responses.
3Records make concise, immutable DTOs for both incoming requests and outgoing error payloads.

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