Hi Guys, 

I am pretty new to Salesforce Apex development and recently I have created a @futurecallout class in Apex which gets invoked by a Lead Trigger (after Insert). In the class i am doing a POST Call (sending Lead Info) and the external system is returning an XML with a message( I am able to see that in debug log). Now I need to parse the same XML data extract a value (UID) and Update the Lead record i am sending to get updated with the value UID as received in XML. 

Please Help

public class WS FromLead {
   
   @future (callout=true)
    public static void sendNotification(id lid, String username) {
        HttpRequest req = new HttpRequest();
        HttpResponse res = new HttpResponse();
        Http http = new Http();
        req.setEndpoint("Endpoint URL");
        req.setMethod('POST');
        req.setHeader('Content-Type','application/x-www-form-urlencoded');
       req.setBody(
        'username='+EncodingUtil.urlEncode(username, 'UTF-8' );  
        req.setTimeout(120000);
        try {
         res = http.send(req);
         System.debug(res.getbody());
         // Generate the HTTP response as an XML stream
         XmlStreamReader reader = res.getXmlStreamReader();
         // Read through the XML
        System.debug('Event Type:' + reader.getEventType());
        if (reader.getEventType() == XmlTag.START_ELEMENT)
           {
            System.debug(reader.getLocalName());
           }
        } 
        catch(System.CalloutException e) {
            System.debug('Callout error: '+ e);
            System.debug(res.toString());
            res.getbody();
        }
        }
        }