Http charset vs xml encoding (utf-8, utf-16, etc)

Which one I should use to parse the xml file. what is the recommended approach to the parse http-xml file. my approach is read xml as String and use DocumentBuilder to parse the String. Is this right approach.

        DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
        Document doc = null;
        InputSource is = null;
        DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
        is = new InputSource(new StringReader(getRawInput()));
        doc = dBuilder.parse(is);