RE: [Springframework-developer] purpose of code in Errors.rejectV alue()

[John C. <joh...@sa...>]

Juergen,

Please see inline.

>=20
> Spring's validator framework is definitely meant to be reusable =
across
> presentation and business logic layers. This is a major USP compared =
to
> Struts' web-centric validation support.
[John Cavacas]=20

Agreed. Which is why I am exploring its use.
>=20
> You can define validator beans in your application context, e.g. a
> "userValidator" bean that implements =
com.interface21.validation.Validator
> and supports your User class. The bean definition can configure the
> validator via its properties. You can assign this bean to respective
> CommandController/FormController implementations as "validator" bean
> reference easily, for web controller validation. This is shown in =
chapter
> 12 of Rod's book.
>=20
[John Cavacas]=20

This is exactly what I have done. However I haven't defined it in a
CommandController/FormController as of yet. As it stands now, the only =
usage
of the validator is in my unit tests, but like you said I will be able =
to
just make it available to my controller and use it.

> Beyond usage in web controllers, you can assign your validator bean =
to any
> business logic services too, easily via bean reference if your =
services
> are registered as beans in your application context. For services =
outside
> of the application context, you could assign the validator bean =
manually
> by getting a reference to the application context, looking up the =
bean,
> and setting it to your service instance. All of this would work in a
> standalone application too, if it utilizes a Spring application =
Context.
>=20
[John Cavacas]=20

Now this is the problem that I am dealing with currently (well I =
haven't had
time to look at it in the past couple of days). My business object is a =
bean
and it is configured by the framework. Let me explain a bit more about =
my
current design. My business object is simply a JavaBean that uses a DAO
object (which in turn makes use of the JDBC and bean Framework). You =
are
right in saying that I can make the validator object also available to =
the
Business Object, however the Business Object is the one responsible for
using the DAO to find out for example, if an email address is already =
in the
database. How do you suggest that the validator have access to that =
kind of
functionality/data? Should it have a reference to the DAO as well? =
Should it
call back the Business Object? That's the issue that I am dealing with =
as it
seems that the separation of concerns becomes mixed up if I do that.=20

Could you perhaps explain how you would solve this problem in more =
detail?
Or rather how the framework Validator can be reused across multiple =
layers.
Maybe I'm just not seeing it.



> Therefore, I don't see a need for validator plug-ins or the like. =
This
> demonstrates the power of the bean factory concept: You can achieve =
so
> much with it so easily.
>=20
> BTW, I assume that the unfinished class in Spring's validation =
package
> that you mentioned is ValidationUtils. This class is meant to be a =
simple
> static utility class that provides low-level validation checks to =
ease
> Validator implementations. Don't confuse this with your Validator
> implementations and their reusability across multiple layers.
[John Cavacas]=20

That was the class that I was referring too and I realize it's not =
finished.

Thanks,
John





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