title: Spring - Best approach to provide specific error messages in a validator from a DAO?
body: <p>What is the best way to implement a validator in Spring that accesses a DAO object but needs to return different error messages based on the DAO error?  Should the DAO method throw different exceptions that the validator turns into proper error messages?  Should the DAO return an enumeration so the validator can handle each return type separately if necessary?  I suppose the validator can pass the org.springframework.validation.Errors object to the DAO, but that seems to tie the two classes too closely together.</p>
  
  <p>I believe the best approach is the enumeration approach to avoid the overhead of exceptions.  Is there another way I should be considering?</p>
  
  <p><strong>Update</strong></p>
  
  <p>Actually, the enumeration would probably have to be a reference passed into the DAO as that method had to return the actual object.  Is this still the best approach?</p>
  
  <p><strong>Update 2</strong></p>
  
  <p>The issue is I need to retrieve information from the database in this particular case, not store it. In the validation class, I was checking if the value already exists (which is why it needed the DAO), and if it already exists that is an error that I would show to the user on the page. I do need to validate that all fields on the form were filled in, so maybe that's the only thing I use the validator for. Then, how do I handle the error where the value already exists in the database? The DAO is the only thing that will know that - what is the best way to communicate that error from the DAO to the web layer?  </p>
  
  <p>The DAO method is currently returning the user object it is retrieving from the database - I can return null if there is an error, but that doesn't give me any granularity into the error details - it's essentially a boolean at that point indicating if the record was found or not, but not why.</p>