Hi
Please find below some of the useful community articles for Server side validations:-
Link:- https://cqwemblog.wordpress.com/2014/01/19/an-approach-for-server-side-validation-in-cq5/
// It talks about An approach for server side validation
Link:- http://help-forums.adobe.com/content/adobeforums/en/experience-manager-forum/aem-forms.topic.html/fo...
// Enable Server-Side Validation
Link:- https://forums.adobe.com/thread/1141475
//server side form validation code for all the field
Yes in CQ you can do both, client and server side validation. More details of form refer [1].
Most of the components have already some build it validation (e.g. 'Required' for 'Text Field' component) and should you need more you can always add some custom validation.
[1] http://dev.day.com/docs/en/cq/current/developing/developing-forms.html
Link:- http://aemtuts.com/aem-sightly-quick-reference/
// Sightly Component with server side Javascript
I hope this would help you.
~kautuk
Kautuk Sahni