CheckCaseValidator.java

package me.test;

import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;

public class CheckCaseValidator implements ConstraintValidator<CheckCase, String> {

    private CaseMode caseMode;

    public void initialize(CheckCase constraintAnnotation) {

        this.caseMode = constraintAnnotation.value();
    }

    public boolean isValid(String object, ConstraintValidatorContext constraintContext) {

        if (object == null) {
            return true;
        }

        if (caseMode == CaseMode.UPPER) {
            return object.equals(object.toUpperCase());
        } else {
            return object.equals(object.toLowerCase());
        }
    }

}