documentBulder.parse(string) returns [#document: null]

import java.io.*;
import java.net.*;

import org.w3c.dom.*;
import org.w3c.dom.Element;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.w3c.dom.NamedNodeMap;
import org.xml.sax.InputSource;
import org.w3c.dom.Text;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

public class GetWeather{
    public static void main(String []arg){
        String path = "http://xml.weather.yahoo.com/forecastrss?
p=INXX0038&u=f";
        try{
            URL url = new URL(path);
            URLConnection urlcon = url.openConnection();

            //int responseCode =urlcon.getResponseCode ( ) ;
            //if ( responseCode ==HttpURLConnection.HTTP_OK) {}

            BufferedReader in = new BufferedReader(new
InputStreamReader(urlcon.getInputStream()));
            String inputLine = null;
            String xmlString = "";
            while ((inputLine = in.readLine()) != null){
                xmlString = xmlString+inputLine;
            }
            //System.out.println(xmlString);
            try{
                parseXml(xmlString);
                //parseXml(urlcon.getInputStream());
            }catch(Exception ex){
                System.out.println("exception in parseXml():-> "+ex);
            }

        }catch(Exception ex){
            System.out.println("exception:-> "+ex);
        }

    }

    public static void parseXml(String xml) throws Exception{
    //public static void parseXml(InputStream xml) throws Exception{
        Document doc;
        DocumentBuilder docBuilder;
        DocumentBuilderFactory docFactory;

        docFactory = DocumentBuilderFactory.newInstance();

        docBuilder = docFactory.newDocumentBuilder();

        doc = docBuilder.parse(new InputSource(new StringReader(xml))); //**
Line abc **/
        //doc = docBuilder.parse(xml);
        System.out.println("doc:-> "+doc); //** Line pqr **/
        Element parentEle = doc.getDocumentElement();

        NodeList nodeList = parentEle.getChildNodes();
        NamedNodeMap nodeAttr = null;
        for(int i=0;i<nodeList.getLength();i++){
            nodeAttr = nodeList.item(i).getAttributes();
            for(int j=0;j<nodeAttr.getLength();j++){
                System.out.println("Node Attr :-
                
System.out.println("----------------");
            }
        }
    }
}

/**Line abc*/ returns null

doc:-> [#document: null]
exception in parseXml():-> java.lang.NullPointerException

why ?
how can i resolve exception