I resolved the issue by converting the source feed from http://www.news18.com/rss/politics.xml to https://www.news18.com/rss/politics.xml
with http below code was creating an empty file which was causing the issue down the line
String feedUrl = "https://www.news18.com/rss/politics.xml";
File feedXmlFile = null;
try {
feedXmlFile =new File("C://opinionpoll/newsFeed.xml");
FileUtils.copyURLToFile(new URL(feedUrl),feedXmlFile);
DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
Document doc = dBuilder.parse(feedXmlFile);