Using validation in Spring to restrict ZonedDateTime field to 3 digits at millisecond time

Question

I have an input DTO in a Spring MVC request that I want to validate, specifically the ZonedDateTime field should at most contain 3 digits at millisecond level, i.e. it cannot be the full nanoseconds precision. Other than that the input request should follow the ISO datetime format. I could make the field a String and then just restrict it with a regex but I prefer to keep it as an ZonedDateTime so I don't need to parse it again.

The object looks like this:

@Data
public class MeasurementDTO {

    private ZonedDateTime date;
    @Digits(integer = 20, fraction = 8) private BigDecimal value;

}

And this is a nested DTO where the parent object comes in as a @RequestBody with the @Valid annotation.

I've tried @JsonFormat but I can't seem to restrict the millisecond part. Is there any way to do this or should I just parse it myself as a String and then deal with it? Or even just leave it at ZonedDateTime and then check the nanosecond component to see if it's there in a custom validator?

Thanks to Tim's answer I remembered Java Dates don't have more precision than millis anyway, so I updated the question to use ZonedDateTimes which do have up to nanosecond precision. I do want to be able to give the user a warning if they do attempt to pass more precision, if using Date this information would just get swallowed.

Answer 1

I did this the hard way with a custom validator. I am still welcoming answers that do this in a more concise way though.

Here's my solution:

I added an annotation @ValidMeasurementInput

@Documented
@Constraint(validatedBy = MeasurementValidator.class)
@Target({TYPE, FIELD, ANNOTATION_TYPE})
@Retention(RUNTIME)
public @interface ValidMeasurementInput {

    String message() default "Invalid measurement input";

    Class<?>[] groups() default {};

    Class<? extends Payload>[] payload() default {};
}

And implemented a custom validator

public class MeasurementValidator implements ConstraintValidator<ValidMeasurementInput, MetricsDTO> {

    @Override
    public boolean isValid(MetricsDTO metricsDTO, ConstraintValidatorContext context) {
        ...
    }
}

Somewhere in this class among some other validations is this code:

   int nano = measurementDTO.getDate().getNano();
   int remainderAfterMillis = nano % 1000000;
   if (remainderAfterMillis != 0)
       valid = false;

And of course I added the @ValidMeasurementInput to my DTO.