Q:

Java fields validation mechanism

Can you recommend any mechanism/technology/3rd party jar that does field validation (like field length validation, regexp validations and so on..)?
It's important that it would be highly configurable - meaning that I would be able to map between fields to a set of validations or something of that sort. 
Perhaps it should have also the ability to implement custom validators.
Any suggestion would be appreciated,
Thank you!

A:

javax.validation (JSF 303 - Bean Validation) 
Hibernate validator is the reference implementation.

