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The Products API validates all incoming create and update request bodies using Jakarta Bean Validation annotations declared directly on ProductRequestDTO. When a request body fails validation, Spring automatically throws MethodArgumentNotValidException before your controller logic runs. GlobalExceptionHandler catches that exception and converts it into a structured 400 response with a field-level error map—no try-catch required in your controller.

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ProductRequestDTO

@Setter
@Getter
public class ProductRequestDTO {

    @NotBlank(message = "Nombre del proudcto es requerido")
    @Size(min = 3, max = 100, message = "El nombre del producto debe tener entre 3 y 100 caracteres")
    private String name;

    @Min(value = 1, message = "El precio del producto debe ser mayor a 0")
    private Double price;

    public ProductRequestDTO() {}

    public ProductRequestDTO(String name, Double price) {
        this.name = name;
        this.price = price;
    }
}

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Validation constraints

FieldAnnotationRuleError message
name@NotBlankMust not be null, empty, or whitespace-onlyNombre del proudcto es requerido
name@Size(min=3, max=100)Length must be between 3 and 100 charactersEl nombre del producto debe tener entre 3 y 100 caracteres
price@Min(1)Must be 1 or greater (effectively > 0 for a Double)El precio del producto debe ser mayor a 0
All three constraints fire independently. If both name and price are invalid, the 400 response includes an entry for each failing field.

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What happens on a validation failure

When the request body violates one or more constraints, the API returns HTTP 400 with the following JSON shape: 
{
  "responseCode": "400",
  "responseMessage": "Error de validación",
  "data": {
    "name": "El nombre del producto debe tener entre 3 y 100 caracteres"
  }
}
The data object is a Map<String, String> where each key is the failing field name and each value is the constraint’s message attribute. Multiple failures appear as multiple keys in the same map.

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Example: sending a bad request

The following request omits price and passes a name that is too short: 
curl -X POST http://localhost:8080/api/v1/products \
  -H "Content-Type: application/json" \
  -d '{"name": "AB", "price": 0}'
Response: 
{
  "responseCode": "400",
  "responseMessage": "Error de validación",
  "data": {
    "name": "El nombre del producto debe tener entre 3 y 100 caracteres",
    "price": "El precio del producto debe ser mayor a 0"
  }
}
Both fields fail simultaneously, and the client receives a single response that lists every issue.

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Activating validation in the controller

Bean Validation only runs automatically when the controller method parameter is annotated with @Valid. Without it, the annotations on ProductRequestDTO are ignored and no validation occurs. Confirm that your controller methods that accept a ProductRequestDTO include @Valid:
@PostMapping
public ResponseEntity<ApiResponse<ProductResponseDTO>> createProduct(
        @Valid @RequestBody ProductRequestDTO dto) {
    ...
}

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Extending with additional constraints

You can add more Jakarta Bean Validation annotations to ProductRequestDTO without touching the controller or the error handler. Common additions include:
  • @DecimalMax / @DecimalMin on price to cap the maximum allowed value
  • @Pattern on name to restrict to alphanumeric characters
  • @NotNull on price to make the field explicitly required (currently a missing price defaults to null and skips the @Min check)
After adding annotations, the 400 response automatically includes the new field’s error message—no other code changes are needed.

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