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From Don Brown <mr...@twdata.org>
Subject [validator] Why doesn't commons-validator include functional validators?
Date Fri, 21 May 2004 20:37:20 GMT
After looking through the different validator usages - Struts, Spring, 
and the unit tests - I'm a bit confused why commons-validator doesn't 
ship with functional validators that can be used directly and not hidden 
by some adapter.  commons-validator contains validator classes, yes, but 
you still need to create a validator adapter class that accepts at least 
the bean and the Field object to interact with the validator.  
Furthermore, this adapter class (Struts and Spring both call it 
CheckFields) contains framework specific references, usually dealing 
with their errors system.

The problem with this approach is it requires huge levels of duplication 
as each container needs to write their own adapter and error creation 
code.  I'm particularly confused because it seems the solution already 
exists within commons-validator - ValidationResult(s).  I would think a 
better approach would be for commons-validator to provide adapters for 
every validator to extract the field information from Field and pass it 
along to the actual validator.  The process of creating messages should 
be left to the class that called validator.validate() to process 
ValidationResults and handle the errors in a container-specific way.  
This way, new containers that want to use commons-validator don't have 
to write their own monolithic adapter class but can use validators as 
they are.  If commons-validator wants to separate a validator into a 
commons-validator adapter class and a actual  validation class, that is 
fine, but there really isn't any need for that adapter to depend on a 
container.

If my premise is sound and the solution agreeable, I would be willing to 
do the leg work of writing container-independent adapters for each of 
the validators.

Don

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