Should I duplicate validation in my MVC layer and Service layer?

Question

I'm feeling a little conflicted at the moment. I have a web application using Stripes for an MVC framework and Spring/Hibernate for the back-end. I have an account registration method in my MVC layer which requires the following validation:

• Username is not already taken
• The provided email address is not already associated with another account

I have a validation method in Stripes (MVC layer) that checks these two cases but was wondering whether my service layer should duplicate these checks? If the service layer interface was exposed as a web service then I think the validation would be a good idea, but if it's only used in the context of a web application is it required?

Edit: I'm not intending to duplicate the validation code - I mean duplicating the validation method calls in two places.

I see my options as:

1. Duplicate the validation calls in both MVC and service layer
2. Only perform this validation in the MVC layer
3. Only perform this validation in the service layer.

What's best practice here? I'm looking for advice/opinions on which option I should go with and why.

Note that there are simple validation checks on the input fields of the registration form (like checking for blanks) and that I think these should be handled by the MVC validation only; I'm only concerned about more complex validations.

Answer 1

Don't duplicate code. Use JSR303 Bean Validation so you can use the same validation logic in all layers of your app.

Hibernate Validator (a separate project from the Hibernate ORM stuff) provides the reference implementation of this interface. It is dead simple to use, you can get started with it very quickly.