Sometimes I just want to apply to a property exactly the same Bean Validator validations I apply to another property.
Point in case: I have a password property in a User class, and there is a ChangePassword data transfer object somewhere else that happens to have currentPassword, newPassword and repeatPassword fields, used precisely to change User.password.
It is obvious that I will want to apply the validations for User.property to all these fields. And, of course, I want changes to validation rules in the original property to be taken into account, automatically.
Copying them is a no-no, because we will violate the DRY (Don’ Repeat Yourself) rule, and creating a custom validation annotation, say @Password, might be overkill. And it would not convey the right meaning, or that’s how I see it.
Creating some kind of DelegateValidation validator that replicates other validations makes a lot of sense, as it clearly conveys the intention and keeps code DRY.
Well, here is the code for the validation annotation itself:
@Target( { ElementType.METHOD, ElementType.FIELD,
ElementType.ANNOTATION_TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = DelegateValidationValidator.class)
@Documented
public @interface DelegateValidation {
Class<?> clazz();
String property();
Class<? extends Payload>[] payload() default {};
String message() default "";
Class<?>[] groups() default {};
}
Here clazz and property are the class and property whose validations we will replicate to validate our own property.
For example, if we have a ValidatedClass like this one,
public static class ValidatedClass {
public static final String OTHER_PROPERTY= "otherProperty";
@Length( min = 3)
@NotNull
@Size(min = 4)
public String otherProperty;
@NotNull
public String getSecondProperty() {
return "hi";
}
}
we can apply the validations in that class otherProperty and secondProperty (corresponding to the getSecondProperty getter) to other properties in our MyClass class as follows:
public static class MyClass {
@DelegateValidation(clazz=ValidatedClass.class,
property=ValidatedClass.OTHER_PROPERTY)
public String value;
@DelegateValidation( clazz=ValidatedClass.class,
property="secondProperty")
public String value;
}
Here is the validator implementation:
public class DelegateValidationValidator implements ConstraintValidator<DelegateValidation, Object> {
private static transient Validator globalValidator;
public static void setGlobalValidator(Validator v ) {
assert v != null;
assert globalValidator == null;
globalValidator = v;
}
@Inject
private transient javax.validation.Validator validator;
private Validator getValidator() {
if( this.validator == null ) {
assert globalValidator != null:
"A validator has not been injected: please, supply one via " +
"setGlobalValidator";
return globalValidator;
}
return this.validator;
}
private Class<Object> referencedClass;
private String property;
// To make happy very demanding compiler with regard to generic parameters
@SuppressWarnings("unchecked")
@Override
public void initialize(DelegateValidation constraintAnnotation) {
// To make happy very demanding compiler with regard to generic parameters
this.referencedClass = (Class<Object>)constraintAnnotation.clazz();
this.property = constraintAnnotation.property();
}
@Override
public boolean isValid(Object value, ConstraintValidatorContext context) {
Set<ConstraintViolation<Object>> constraints =
getValidator().validateValue(this.referencedClass,
this.property, value);
if( constraints.isEmpty() ) {
return true;
}
context.disableDefaultConstraintViolation();
for( ConstraintViolation<Object> c : constraints) {
context.buildConstraintViolationWithTemplate(
c.getMessage()).addConstraintViolation();
}
return false;
}
}
Here we must get access to the Validator we are using to peform validations to ask it to perform validations against the tracked property. Since I use CDI, as well as the Seam validtor module, I rely on them to inject the right Validator instance in my validator implementation.
However, if you are not using CDI/Seam, or just to make testing easier, I am providing a way to supply a validator via the setGlobalValidator method, that you should call before any validations are performed.
Last but not least, let me tellyou that, if you provide a wrong property name for the validator, the validation will fail with a ValidationException, as attested by some of the following tests.
The tests
For the sake of completeness, here are my tests, written against TestNg:
public class DelegateValidationTest {
public static class ValidatedClass {
public static final String OTHER_PROPERTY= "otherProperty";
@Length( min = 3)
@NotNull
@Size(min = 4)
public String otherProperty;
@NotNull
public String getSecondProperty() {
return "hi";
}
private Integer propertyWithNoValidations;
}
private Validator validator;
@BeforeClass
void classSetUp() {
if( this.validator == null ) {
this.validator = Validation.buildDefaultValidatorFactory().getValidator();
DelegateValidationValidator.setGlobalValidator(this.validator);
}
}
public static class MyClass {
@DelegateValidation(clazz=ValidatedClass.class, property=ValidatedClass.OTHER_PROPERTY)
public String value;
}
@Test
public void testValueValidation() {
Assert.assertEquals( this.validator.validateValue(
MyClass.class, "value", null).size(), 1);
Assert.assertEquals( this.validator.validateValue(
MyClass.class, "value", "ab").size(), 2);
Assert.assertEquals( this.validator.validateValue(
MyClass.class, "value", "abc").size(), 1);
Assert.assertTrue( this.validator.validateValue(
MyClass.class, "value", "abcd").isEmpty());
}
@Test
public void testWholeBeanValidation() {
ConstraintViolation<MyClass> firstV;
ConstraintViolation<MyClass> secondV;
Iterator<ConstraintViolation<MyClass>> it;
MyClass mc = new MyClass();
mc.value = "ab";
Set<ConstraintViolation<MyClass>> violations =
this.validator.validate(mc);
Assert.assertEquals( violations.size(), 2);
it = violations.iterator();
firstV = it.next();
secondV = it.next();
// We expect MyClass, even if validations are run
// against ValidatedClass
Assert.assertEquals( firstV.getRootBeanClass(),
MyClass.class);
// We expect "value", even if validations are run
// against "otherProperty"
Assert.assertEquals( firstV.getPropertyPath().toString(),
"value");
// We expect MyClass, even if validations are run
// against ValidatedClass
Assert.assertEquals( secondV.getRootBeanClass(),
MyClass.class);
// We expect "value", even if validations are run
// against "otherProperty"
Assert.assertEquals( secondV.getPropertyPath().toString(),
"value");
}
public static class MyClassWithWrongDelegationProperty {
@DelegateValidation(clazz=ValidatedClass.class,
property="wrongPropertyName")
public String value;
}
@Test(expectedExceptions={ValidationException.class})
public void testReferencePropertyDoesNotExist() {
this.validator.validateValue(
MyClassWithWrongDelegationProperty.class, "value", "ab");
}
public static class MyClassTrackingGetter {
@DelegateValidation( clazz=ValidatedClass.class,
property="secondProperty")
public String value;
}
@Test
public void testWorksWithGetters() {
Assert.assertEquals( this.validator.validateValue(
MyClassTrackingGetter.class, "value", null).size(), 1);
Assert.assertTrue( this.validator.validateValue(
MyClassTrackingGetter.class, "value", "a").isEmpty());
}
public static class MyClassTrackingPropertyWithNoValidations {
@DelegateValidation( clazz=ValidatedClass.class,
property="propertyWithNoValidations")
public Integer value;
}
@Test
public void testWorksWithPropertyHavingNoValidations() {
Assert.assertTrue( this.validator.validateValue(
MyClassTrackingPropertyWithNoValidations.class, "value", null).
isEmpty());
}
}
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