Server Side Validations in form AEM 6.2

Hi Ankur - Did you try "Enable server validation" property?

https://helpx.adobe.com/aem-forms/6/configuring-submit-actions.html#ServerSideRevalidationinAdaptiveForm

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/forum__egmg-hi_i_want_toena.html

// 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