Smooks 1.2 adds support for message data Validation as one of its new features. This new feature allows you to perform strong field and fragment validation on not just XML data, but also on EDI, JSON, CSV etc. It currently supports Regex and MVEL rules bases (Drools to follow). Regex rules allow you to perform low level field format validation, while MVEL rules allow you to perform Business rules validation at a fragment/message level.
Vivek Tomar has written an interesting blog on using Smooks to perform Java to Java transforms. Vivek works for NAXOS Software Solutions.