how to validate the maxLength restriction

I have added the new attribute maxLength in ClassificationAttribute Item type I need to Validate if product is part of classifying attribute and the classification attribute length restriction. In Details: - Invoke the custom validation service: CustomAttributeValidationService. If the product is part of classification attributeassignment for that attribute, fetch the maxLength attribute from ClassificationAttribute and validate with the input attribute. - If the input attribute length field exceeds the maxLength attribute, throw custom exception CustomAttributeLengthException with appropriate message. Please any one help me on this