We Keep Coding

ConstraintValidation not getting applied to the list

I have List of Objects that I need to run some validation on
#KeyValid
#Valid
protected List<KeyValue> keyValues;
and I have a the following annotation created for it:
#Target({ElementType.TYPE, ElementType.FIELD})
#Retention(RetentionPolicy.RUNTIME)
#Constraint(validatedBy = KeyValidator.class)
public #interface KeyValid{
String message() default "invalid_parameter_default_message";
String[] checks() default {};
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}
And this is my validator:
public class KeyValidator implements ConstraintValidator<KeyValid, KeyValue> {
#Override
public void initialize(KeyValid keyValid) {
}
#Override
public boolean isValid(KeyValue keyValue, ConstraintValidatorContext constraintValidatorContext) {
return true;
}
}
I had read somewhere that collections can be validated in bulk if the list or map or set is annotated by custom constraint then all of the elements of the collection call the validator but the above code throws the following error
javax.validation.UnexpectedTypeException: HV000030: No validator could be found for constraint 'com.util.Validators.KeyValid' validating type 'java.util.List<com.model.KeyValue>'. Check configuration for 'keyValue'

Your constraint would get the actual List passed not its elements. If you are using Java 8 and the latest version of Hibernate Validator, you can use type argument constraints. You just have to make sure to also add ElementType.TYPE_USE to #Target in your constraint. Type argument constraints are not yet official part of Bean Validation, but will be in the next version of it (BV 2.0).
You would have something like this:
protected List<#KeyValid KeyValue> keyValues;
Alternatively, could you not put the #KeyValid constraint as class level constraint on KeyValue?

Is it possible to add custom property to java bean validation annotation?

Like that
#NotNull(code=10000)
#Size(min=5, max=10, code=10001)
Java bean validation has 3 properties: message, payload and groups. I wanna add a new one: code.
I've checked some docs, like https://docs.jboss.org/hibernate/validator/5.0/reference/en-US/html/validator-customconstraints.html and https://docs.oracle.com/javaee/6/tutorial/doc/gkfgx.html. It seems not possible?

Short answer to your question: No, you can't just add an extra field, nor can you use inheritance too add the extra field. See this question which explains why Java doesn't allow inheritance with annotations.
What you'll have to do is create your own particular version of the #Size annotation. But you should be able to apply the #Size annotation to your custom annotation so that #Size is checked automatically when you run your validations.
Your annotation would probably look something like this:
#Constraint(validatedBy = { })
#Target({ElementType.FIELD, ElementType.PARAMETER})
#Retention(RetentionPolicy.RUNTIME)
#ReportAsSingleViolation
//The only downside of this approach
//is that you have to hardcode your min and max values
#Size(min=5, max=10)
public #interface CodedSize {
String message() default "{Default Validation Message}";
Class<?>[] groups() default { };
Class<? extends Payload>[] payload() default { };
int code() default 0;
}
If you wanted to specify the size as well in the annotation, you could do that, and write a custom validator that validates your annotation.
#Constraint(validatedBy = { CodedSizeValidator.class })
#Target({ElementType.FIELD, ElementType.PARAMETER})
#Retention(RetentionPolicy.RUNTIME)
public #interface CodedSize {
String message() default "{Default Validation Message}";
Class<?>[] groups() default { };
Class<? extends Payload>[] payload() default { };
int minSize() default 5;
int maxSize() default 10;
int code() default 0;
}
Then your custom validator looks something like this:
public class CodedSizeValidator implements ConstraintValidator<CodedSize, String> {
private int minSize;
private int maxSize;
private int code;
#Override
public void initialize(CodedSize constraintAnnotation){
this.minSize = constraintAnnotation.minSize();
this.maxSize = constraintAnnotation.maxSize();
this.code = constraintAnnotation.code();
}
#Override
public boolean isValid(String value, ConstraintValidatorContext context) {
boolean isValid = false;
if(value == null || value.isEmpty()) {
//if a null or empty value is valid, then set it here.
isValid = true;
} else {
//Logic here to determine if your value is valid by size constraints.
}
return isValid;
}
}
I used String because that seemed the most applicable, but you could easily use Number, or even a generic type to allow you to use this annotation on more than one field. The advantage of doing it this way is that if you want to add a null check in with this validation, you can do so.
The ConstraintValidatorContext can be used to build out your error message if multiple validations fail. You can make this as detailed as you want, but be aware that this code can spaghetti-fy very quickly.

How to set default group in bean validation context

I'm working with bean validations and I'm searching for a possibility to set a default group of my own bean validation annotation.
I have something (working) like this:
Application.class (calling validate on MyBean)
public class Application {
public static void main(String[] args) {
Validator validator = Validation.buildDefaultValidatorFactory().getValidator();
Set<ConstraintViolation<MyBean>> violations =
validator.validate(new MyBean(), SecondStep.class);
}
}
MyBean.class (the bean itself; here is what I want to prevent)
public class MyBean {
// I don't want to write this "groups" attribute every time, because it's very clear,
// that this should only be validated for the second step, isn't it?
#RequiredBySecondStep(groups=SecondStep.class)
private Object myField;
}
RequiredBySecondStep.class (the bean validation annotation)
#Documented
#Target(FIELD)
#Retention(RUNTIME)
#Constraint(validatedBy = RequiredBySecondStepValidator.class)
public #interface RequiredBySecondStep {
String message() default "may not be null on the second step";
Class<?>[] groups() default {}; // <-- here I want to set SecondStep.class
Class<? extends Payload>[] payload() default {};
}
RequiredBySecondStepValidator.class (an implemented constraint validator)
public class RequiredBySecondStepValidator implements ConstraintValidator<RequiredBySecondStep, Object> {
public void initialize(RequiredBySecondStep constraintAnnotation) {
}
public boolean isValid(Object object, ConstraintValidatorContext constraintContext) {
return object != null;
}
}
SecondStep.class (the bean validation group)
public interface SecondStep {
}
Unfortunately, it's not possible by specification, to set the default group in the RequiredBySecondStep annotation like this:
Class<?>[] groups() default SecondStep.class;
// and using just the following in the bean:
#RequiredBySecondStep
private Object myField;
This will result in a RuntimeException:
javax.validation.ConstraintDefinitionException: Default value for
groups() must be an empty array
Furthermore, there is not only a SecondStep. There are probably 5 different groups which I want to annotate directly with a #RequiredByFirstStep or #RequiredByFifthStep.
Is there a good way to implement this?

I think you got it all a bit wrong. There is indeed to way to do what you want and that's because the aspect of constraints and their validation via a ConstraintValidator is orthogonal to groups and groups sequences. Per design a constraint (annotation and its validator) should be independent of the group getting validated. Even if you would get this to work, it would not be portable constraints. Personally, I would re-think what you want to achieve. #RequiredByFirstStep does not tell you what the requirement is. You should develop constraints which imply what they are valiating (a string length, not null, etc), when or better in which condition they are executed is a then controlled by group interfaces.

Bean validation: at least one element of a list must have one field filled

I have a list of lets say Car objects. Each car has a miles member.
I need to validate (using Hibernate Validator) that at least one car in my list has a not null miles member. The best solution would be an annotation that would apply to all the elements of a collection, but would validate in the context of the whole collection.
I have two questions:
Is there already an annotation for this (I do not know of any)?
If there is no annotation for this, is there a way to create an generic annotation?
I thought of specifiyng the name of the field that has to be not null at least for one element in the list, then I can apply this not only for Car classes.
public class VechicleTransport {
#AtLeastOneNotNull( fieldName = "miles" )
private List<Car> carList;
}
public class Car {
private Double miles;
....
}

AFAIK there is no such annotation, You need to define custom constraint annotations and define your validation logic inside it.
Like
Defining custom constraint annotation AtLeastOneNotNull
#Target({ElementType.FIELD})
#Retention(RetentionPolicy.RUNTIME)
#Documented
#Constraint(validatedBy=AtLeastOneNotNullValidator.class)
public #interface AtLeastOneNotNull{
String message() default "Your error message";
Class<!--?-->[] groups() default {};
Class<!--? extends Payload-->[] payload() default {};
}
Defining validator for custom annotation.
public class AtLeastOneNotNullValidator implements ConstraintValidator<AtLeastOneNotNull, object=""> {
#Override
public void initialize(AtLeastOneNotNull constraint) {
}
#Override
public boolean isValid(Object target, ConstraintValidatorContext context) {
// Add logic to check if atleast one element have one field
}
}
Link for more details

Variable field in a constraint annotation

I need to create a custom constraint annotation which can access the value of another field of my bean. I'll use this annotation to validate the field because it depends on the value of the other but the way I define it the compiler says "The value for annotation attribute" of my field "must be a constant expression".
I've defined it in this way:
#Target(ElementType.FIELD)
#Retention(RetentionPolicy.RUNTIME)
#Constraint(validatedBy=EqualsFieldValidator.class)
#Documented
public #interface EqualsField {
public String field();
String message() default "{com.myCom.annotations.EqualsField.message}";
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}
public class EqualsFieldValidator implements ConstraintValidator<EqualsField, String>{
private EqualsField equalsField;
#Override
public void initialize(EqualsField equalsField) {
this.equalsField = equalsField;
}
#Override
public boolean isValid(String thisField, ConstraintValidatorContext arg1) {
//my validation
}
}
and in my bean I want something like this:
public class MyBean{
private String field1;
#EqualsField(field=field1)
private String field2;
}
Is there any way to define the annotation so the field value can be a variable?
Thanks

The easiest thing to do is take one step back: the constraint/validator you have written works on a field-level, but what you want to enforce is a cross-field dependency i.e. a class-level constraint.
Rewrite your constraint and validator to work at the class level (i.e. the annotation will go on the class, not on the field). That way you'll get access to the entire class. In your isValid(..) method, simply do a get on both the fields, compare, and return appropriately.

As the compiler said annotations must be constant (i.e. you can determine the value at compile time.) Now If I'm guessing correctly it looks like you are using this annotation to denote that the values of those fields should be equal when run through the equals field validator. One approach you could take is using reflection. Instead of trying to annotate with the value, annotate with the field name instead
public class MyBean{
private String field1;
#EqualsField("field1")
private String field2;
}
Then in your validator you can read the name of the field and use reflection to access it
Object o = object.getClass().getDeclaredField(annotationValue).get(object);
o == object.(field with annotation) OR
o.equals(object.(field with annotation));
Depending on what you are trying to do you may need to add in logic based on the field type, but still the same general principle.

Check out this previous question, has multiple solutions for cross-field validation: Cross field validation with Hibernate Validator (JSR 303)