How to get Json from the Magento JsonResultFactory Class

<?php

namespace Webkul\<Modulename>\Framework\Controller\Result;

/**
 *  Inherited 
 * */
class Json extends \Magento\Framework\Controller\Result\Json
{ 
    /**
     * GetJsonData function
     *
     * @return void
     */
    public function getJsonData()
    {
        return $this->json;
    }

    /**
     * GetData function
     *
     * @return void
     */
    public function getData()
    {
        return \Zend_Json::decode($this->json);
    }
}

    <preference for="Magento\Framework\Controller\Result\Json" type="Webkul\PosMultiFee\Framework\Controller\Result\Json" />