Validating Input
Understand the importance of validating input within the application layer to ensure data integrity in hexagonal architecture. Explore how input models like SendMoneyCommand handle validation, leverage Java Bean Validation annotations, and maintain use case purity by preventing invalid data from reaching core business logic.
We'll cover the following...
While validating input is not a responsibility of a use case class, it belongs in the application layer, so this is the place to discuss it.
Why not let the calling adapter validate the input before sending it to the use case? Well, do we want to trust the caller to have validated everything as is needed for the use case? Also, the use case might be called by more than one adapter, so the validation would have to be implemented by each adapter and one might get it wrong or forget it altogether.
The application layer should care about input validation because if it does not, it might get invalid input from outside the application ...