Validation Model

Question

Hi,
I�m on the final project of my degrees. I have to develop a system to generate client side validations and server side validations for n-tiers Java applications. The principal objective of the project is: write the validations rules ones and use it for validations in the client side (JavaScript) and the server side (Java).
I�m over the research stage and searching for the possible solutions that the Java technologies proposes for this problem. I know that JSF has a �Validation Model� that maybe resolve the problem, probably only part of it. I need to evaluate the possibilities to integrate this existing solution with my work, but first y have to make sure that I�m not fighting with JSF Validation Model, this is not the idea.
The problem that I found was the poor official information that explain how the validations works, probably because JSF is in a very early realize. I mean, I find a lot of information in the Internet but I need an official voice, so I can justify why I will not use the standard solution (JSF) or why I�ll use it.
1)     The validation model generate client side validations (for example JavaScript) ?. If not, do you think that a feature like this can be included in the next release of JSF?.
2)     The validations runs on the server side. Do they run on the web-tier or on the business-tier?
3)     I need to now the plans for the future, what do I�ll expect for JSF Validation Model now to 6-8 months?
4)     Is there a way to make validation rules using different fields, for example, validate one field based on the value of another field.
Thanks, Elena.

Answer 1

I'll try to answer your questions;
1) The validation model generate client side validations (for example JavaScript) ?. If not, do you think that a feature like this can be included in the next release of JSF?.
This is unlikely to change for the RI, however the spec does not care where the validations take place so long as they follow the spec. So I could see some JSF vendor suppling an implemenation that did generate JavaScript for client side validations but also performed the Web Tier validations as described in the spec.
2) The validations runs on the server side. Do they run on the web-tier or on the business-tier?
JSF only addresses the web-tier.
3) I need to now the plans for the future, what do I�ll expect for JSF Validation Model now to 6-8 months?
I susspect that things in the validation area will not changes much in the next 6 months.
4) Is there a way to make validation rules using different fields, for example, validate one field based on the value of another field.
You could fairly easily write a custom validator that validated several fields in relation to each other. In the JSP I could see something like this.
<h:input_number ......
<f:validator type="foo.bar.MyValidator>
<f:attribute name="attrOne" value="propertyReference.one"/>
<f:attribute name="attrTwo" value="propertyReference.two"/>
</f:validator>
</h:input_number>
Then the MyValidator could use the attributes (attrOne and attrTwo) set on the component (a UIInput in this case) to lookup the values to validate against.
This thread has info on how to use the property references to get at the actual values;
http://forum.java.sun.com/thread.jsp?forum=427&thread=427896&message=1908077#1908077
From what it sounds like that you want to do I'd suggest perhaps writing an extension to XDoclet that would allow you to specify the validation once and have XDoclet generate the code for a custom renderer that would generate JavaScript as well as making java code that you could invoke from your validator and your back-end business logic. Extending XDoclet is supposed to be easy (although I have not done it personally yet) the hard part would be defining the proper semantics in your 'constraint language' so that you could generate propery JavaScript and Java.
Good luck,
-bd-
http://bill.dudney.net