1. rails.validations.customValidators.js, new file rails.validations.cus...

1. rails.validations.customValidators.js, new file rails.validations.customValidators.js
2. manage.js, load rails.validations.customValidators.js
3. product.rb, add error message
4. url_validator.rb, it is a empty class. just let rails know app use this custom validator