问题
I noticed that all built-in constraints have an empty value for the validatedBy parameter in @Constraint. i.e. @Constraint(validatedBy = {})
First, why are they allowed to have an empty value for validatedBy? I thought you can leave it blank only for constraint composition that does not need addtional validation?
Also, note that the Hibernate Validator can still find a validator implementation class for each built-in constraint, despite the validatedBy is empty, but if I leave the validatedBy blank for my constraint, my custom validator never gets picked up. Why is that?
Thanks.
回答1:
Those built-in are treated in special implementation-specific way and their validators are configured programmatically.
For Hibernate Validator it's done in ConstraintHelper.java. I think you can't achieve the same for your custom constraints.
回答2:
Maybe have a look at this answer:
How to avoid cross dependency between layers because of @Constraint validatedBy?
And those two links:
Adding constraints programmatically: http://docs.jboss.org/hibernate/stable/validator/reference/en-US/html/validator-specifics.html#section-programmatic-api
Adding constraints per xml: http://docs.jboss.org/hibernate/validator/4.1/reference/en-US/html/validator-xmlconfiguration.html
来源：https://stackoverflow.com/questions/4512826/empty-validatedby-in-constraint