How to add ConstraintViolations to list element at index i with custom ConstraintValidator

Question

I'm currently working on a custom ConstraintValidator to check an array of objects which have a timespan associated with them for overlaps in their timespan. The validation logic is working, however, I am uncertain how to add a "This object's timeslot overlaps with another object's timeslot" message to every object in violation of the validation logic.

I've tried several approaches described here: https://docs.oracle.com/javaee/7/api/javax/validation/ConstraintValidatorContext.html

Specifically those described in the buildConstraintViolationWithTemplate method docs.

Here is the relevant section of the code:

@Override
public boolean isValid(List<Shift> shifts, ConstraintValidatorContext context) {

List<Integer> overlappingShiftIndices = determineOverlappingShifts(shifts);

if (!overlappingShiftIndices.isEmpty()) {
  log.debug("Overlap validation failed.");

  context.disableDefaultConstraintViolation();
  // Moving the error from form-level to fields
  for (int index : overlappingShiftIndices) {
    context.buildConstraintViolationWithTemplate("{com.generali.standbyscheduler.validation.shiftlist.overlap}")
           .addBeanNode()
           .inIterable().atIndex(index)
           .addConstraintViolation();
  }

  return false;
}

log.debug("Overlap validation succeeded.");
return true;
}

As you can see I tried the .addBeanNode().inIterable().atIndex(index) approach here. When looking at the ConstraintViolations the property path displays as list[index]. Is this correct?

I plan on using this to access the determined violations from a BindingResult in a Thymeleaf template and am uncertain whether the violations will be accessible this way. The list will be a property of another bean, so I'm expecting to read the violations using a path like propertyNameOfList[index]. Or would it be propertyNameOfList.list[index] or something else?

Answer 1

I got the same problem, when trying to validate if certain fields are unique within a object list. My own solution (I found none on the internet :/ ):

You have to overwrite the current PropertyNode and add the index number by using .addPropertyNode(null).inIterable().atIndex(index). Example:

ConstraintAnnotation:

@Target({ElementType.FIELD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = UniqueBusinessIndexValidator.class)
public @interface UniqueEntries {

    String message() default ValidationMessages.REQUIRED_UNIQUE_INDEX;
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

ConstraintValidator:

public class UniqueBusinessIndexValidator implements ConstraintValidator<UniqueEntries, List<HasBusinessIndex>> {

    @Override
    public boolean isValid(List<HasBusinessIndex> collection, ConstraintValidatorContext context) {
        if (collection == null || collection.isEmpty()) {
            return true;
        }

        Map<String, List<Integer>> indexesMap = new HashMap<>();
        for (int runner = 0; runner < collection.size(); runner++) {
            String businessIndex = collection.get(runner).getBusinessIndex();
            if (indexesMap.containsKey(businessIndex)) {
                indexesMap.get(businessIndex).add(runner);
            } else {
                indexesMap.put(businessIndex, new ArrayList<>(List.of(runner)));
            }
        }

        boolean isValid = indexesMap.values().stream().noneMatch(indexes -> indexes.size() > 1);
        if (!isValid) {
            indexesMap.values()
                      .stream()
                      .filter(index -> index.size() > 1)
                      .forEach(index -> addUniqueBusinessIndexkennungViolation(context, index));
        }
        return isValid;
    }

    private void addUniqueBusinessIndexkennungViolation(ConstraintValidatorContext context, List<Integer> indexes) {
        for (Integer index : indexes) {
            context.buildConstraintViolationWithTemplate(ValidationMessages.REQUIRED_UNIQUE_INDEX)
                   .addPropertyNode(null)
                   .inIterable()
                   .atIndex(index)
                   .addPropertyNode("businessIndex")
                   .addConstraintViolation()
                   .disableDefaultConstraintViolation();
        }
    }