server-side, java-based validation rules for struts..

[Levi Cook <le...@papajo.com>]

I believe its well established that Struts would benefit from a good
validation framework (duh, right?). While there are a number of
really good ideas floating around, some seem to be introducing
unnecessary complexity (IMHO, of course)

Getting to the point, I think constrained properties from the
JavaBeans spec. provides a built in, flexible foundation for
struts invoked validation.
(http://java.sun.com/products/javabeans/docs/spec.html)

key advantages:
  * support is provided by the standard java.beans package
  * it doesn't require learning anything proprietary (even though
    other solutions are very cool :)
  * its conceptually simple; ie. before accepting a new value,
    the bean/ActionForm's setter method(s) ensures its accepted by
    all registered listeners before commiting the value
    (java.bean.VetoableChangeListenter).
  * and finally, its wide open for extension (key since we can't
    predict all validation scenario's, right?)

I also believe that integration with Struts could be pretty straight
forward. In a nutshell, we could make 2 modifications ActionServlet:

  1. Make it responsible for registering "change-listeners"
  2. Make it handle PropertyVetoException(s) thrown by setter methods
     (primarily by turning them into ActionErrors)

Prior to making a "formal" proposal for this, I thought it might be
useful to consider the attached code fragments:

Then again, maybe I'm way off and should be ignored- If I am,
let me know..

Regards,
Levi Cook