I found out that cross-parameter constraints were not supported by hibernate annotation processor. In the example provided, the processor was trying to compare Object or Object[] to the return type of the method, not to the parameters.

I've implemented the support for cross-parameter constraints, added most of the checks and related test cases.

The code is attached to the following pull request: https://github.com/hibernate/hibernate-validator/pull/455

Thanks for the response Gunnar. I would very much like to contribute a fix, however, am working on new product development at the moment and on a pretty tight schedule. I will try and find some time to create the fix but cannot promise it will be any time soon. The good thing is that the issue is not a blocker and there is a workaround that I can use for now.

Hi Georgios, thanks for reporting this issue. The annotation processor does not yet support method/constructor constraints and thus cross-parameter constraints. Good to hear that you found a workaround for the time being.

That said, would you be interested in contributing a fix for this? The processor code base is quite straight-forward so it would be a great chance if you'd like to dive a bit into Hibernate Validator development If you're interested I could give you some guidance on the general design and how to get started.

Changing the type parameter from Object[] to Object in CrossParameterConstraintValidator seems to do the trick. However, the issue still applies for the case when Object[] type parameter is used. As mentioned in cross-parameter constraint documentation: The type parameter T from the ConstraintValidator interface must resolve to either Object or Object[] in order to receive the array of method/constructor arguments in the isValid() method.