Business logic validation patterns & advices

Question

I have two layers of validation in my application. First is entity validation performed by bean validation API (e.g. required fields). The second level is business logic val

Answer 1

Strategy pattern is the solution in my opinion. I will give you a very simple example. Lets say we have two kinds of credit cards, Visa and Mastercard. The logic to perform payment operation is the same for both cards, but card number validation is different. So, by passing VisaStrategy object through a workflow does the same logic and operations as we would pass MastercardStrategy, except one thing - card number validation, which is done inside each defined Strategy class, so you do not have any "if else" stuff in your code at all. Each Strategy class is now responsible for one and only one type of card validation. If you look for flexible and easy to maintain code structure - use Strategy design pattern.