On click on confirm ajax submit this form, and wherever your redirect in your class the ajax will redirect just the portlet.

<portlet:actionURL var="ajaxURL" name="atsglobaltechsoft" windowState="< %= LiferayWindowState.EXCLUSIVE.toString()%>" />

<script type="text/javascript" >
    function submitForm(){
        jQuery.ajax({
          type: 'POST',
          url: '<%= ajaxURL % >',
          success: function(data){
              jQuery('#p_p_id<portlet:namespace/ > .portlet-content').html(data);
          }
        });
    }
</script >

<form action="" name="fm" id="fm" method="post">
    <a href="#" onclick="submitForm();">confirm < /a>
</form>