1. JSR-303
Bean Validation

2. Spring MVC Validator
public interface Validator {
boolean supports(Class<?> clazz);
void validate(Object target, Errors errors);
}

3. Spring MVC Validator
● Spring MVC specific
● Can not be used on client side
● All validation goes to single method
● Hard to make unit tests

4. Description
"This JSR will define a meta-data model and API
for JavaBeanTM validation based on annotations,
with overrides and extended meta-data through
the use of XML validation descriptors."

5. Key points
● Configured with annotations
● Not tied to a specific application tier
● Suits both server and client side

6. Implementations
● Hibernate Validator (reference implementation)
● Apache Bean Validation (incubation)
● GWT Validation

7. Annotation samples
@Min @Future @Null
@Past
@NotNull
@Digits
@MyCustomMegaConstraint
@Max
@Size
@Pattern

8. Custom constraint sample
@Target(TYPE)
@Retention(RUNTIME)
@Constraint(validatedBy = UniqueProductInOrderValidator.class)
public @interface UniqueProductInOrder {
String message() default "Only unique items";
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}

9. Bean sample
@UniqueProductInOrder
public class Item {
private String product;
@Valid private Order order;
@NotBlank
@Length(min = 5, max = 30)
public String getProduct() {
return product;
}
}

10. Validator sample
public class UniqueProductInOrderValidator implements
ConstraintValidator<UniqueProductInOrder, Item> {
@Override
public boolean isValid(Item v, ConstraintValidatorContext c) {
Collection<Item> items = value.getOrder().getItems();
Set<Item> set = new HashSet<Item>(items);
return set.size() == items.size();
}
}

11. Invoke validation sample
@RequestMapping(method = POST)
public String create(@Valid Item item) {
orderRepository.update(item.getOrder());
return "redirect:/orders/" + item.getOrder().getId();
}
@ExceptionHandler(BindException.class)
public ModelAndView itemHasErrors(BindException e) {
return new ModelAndView("addItem", e.getModel());
}

12. Another sample
@RequestMapping(value = "/orders", method = POST)
public String create(@Valid Order order, BindingResult errors) {
if (errors.hasErrors()) {
return null;
}
orderRepository.save(order);
return "redirect:/orders";
}

13. Groups sample
@GroupSequence({ Item.class, ComplexValidation.class })
@UniqueProductInOrder(groups = ComplexValidation.class)
public class Item {
@NotBlank
private String product;
}
interface ComplexValidation {}

14. Service layer validation
public class SomeService {
@Inject
private Validator validator;
public void doSomething(Item item) {
Set<ConstraintViolation<Order>> violations =
validator.validate(item);
}
}

15. Unit test sample
@Test
public void noValidationErrorsWhenItemIsValid() {
Item item = new Item(order, "x", 0);
Validator validator =
Validation.buildDefaultValidatorFactory().getValidator();
Set<ConstraintViolation<Item>> violations = validator.validate(item);
assertTrue(violations.isEmpty());
}

16. Single property unit test sample
@Test
public void nullProductIsNotAllowed() {
Item item = new Item(order, null, 0);
Validator validator =
Validation.buildDefaultValidatorFactory().getValidator();
Set<ConstraintViolation<Item>> violations =
validator.validateProperty(item, "product");
assertFalse(violations.isEmpty());
}

17. Hibernate Validator Annotation
Processor
Annotation processor based on JSR-269 which plugs
into the build process and raises compilation errors
whenever constraint annotations are incorrectly used.

18. https://github.com/aleksz/spring-
reference