Is there an annotation for java validate if the value of a field in a List of Objects is duplicated? - spring-boot

Question

I have a List of Objects and each Object have an email, I'd like to validate if the email is duplicated in this list.
#PostMapping
#ResponseStatus(HttpStatus.CREATED)
Father create(#PathVariable String id,
#Valid #RequestBody Father father) {
...
}
Father will have a list of child:
private List<Child> childs;
Each child will have an email:
public class Child {
...
#NotEmpty
private String email;
...
}
I'd like to validate if for example there is a request body with 2 child with the same email.
Is it possible or only validating after receive and process the payload?

Answer 1

Edited
For validating the child emails list, you can create a custom validation.
I coded a custom validation as follows
1- Create annotation named ChildEmailValidation
#Documented
#Constraint(validatedBy = ChildEmailValidator.class)
#Target( { ElementType.METHOD, ElementType.FIELD })
#Retention(RetentionPolicy.RUNTIME)
public #interface ChildEmailValidation {
String message() default "Duplicate Email";
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}
2- Create a validator for ChildEmailValidation
In this part, you can write your custom business for validation. (You can write your algorithm)
public class ChildEmailValidator implements ConstraintValidator<ChildEmailValidation, List<Child>> {
#Override
public void initialize(ChildEmailValidation constraintAnnotation) {
}
#Override
public boolean isValid(List<Child> childList, ConstraintValidatorContext constraintValidatorContext) {
//Create empty mailList
List<String> mailList = new ArrayList<>();
//Iterate on childList
childList.forEach(child -> {
//Checks if the mailList has the child's email
if (mailList.contains(child.getMail())) {
//Found Duplicate email
throw new DuplicateEmailException();
}
//Add the child's email to mailList (If duplicate email is not found)
mailList.add(child.getMail());
});
//There is no duplicate email
return true;
}
}
3- Add #ChildEmailValidation in Father class
public class Father {
List<Child> child;
#ChildEmailValidation
public List<Child> getChild() {
return child;
}
public void setChild(List<Child> child) {
this.child = child;
}
}
4- Put #Valid on fatherDto in the controller
#RestController
#RequestMapping(value = "/test/", method = RequestMethod.POST)
public class TestController {
#RequestMapping(value = "/test")
public GenericResponse getFamily(#RequestBody #Valid Father fatherDto) {
// ...
}
}

Answer 2

You can use #UniqueElements annotation of Hibernate that you can find on this documentation this is based on equals of some element.
#UniqueElements
private List<Child> childs;