Parse XML with namespaces in Java using xpath

I am trying to parse SOAP request in java but code is not returning any nodes here is the code can anybody find error

        String xml="<soapenv:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soapenv=\"http://schemas.xmlsoap.org/soap/envelope/\" xmlns:ser=\"http://services.web.post.list.com\"><soapenv:Header><authInfo xsi:type=\"soap:authentication\" xmlns:soap=\"http://list.com/services/SoapRequestProcessor\"><!--You may enter the following 2 items in any order--><username xsi:type=\"xsd:string\">dfasf@google.com</username><password xsi:type=\"xsd:string\">PfasdfRem91</password></authInfo></soapenv:Header></soapenv:Envelope>"; 
    System.out.println(xml);
    DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
    domFactory.setNamespaceAware(true);
    DocumentBuilder builder = domFactory.newDocumentBuilder();
    Document doc = builder.parse(new InputSource(new StringReader(xml)));
    XPath xpath = XPathFactory.newInstance().newXPath();
    // XPath Query for showing all nodes value

    try
    {
    XPathExpression expr = xpath.compile("/soapenv:Envelope/soapenv:Header/authInfo/password");
    Object result = expr.evaluate(doc, XPathConstants.NODESET);
    NodeList nodes = (NodeList) result;
    System.out.println("Got " + nodes.getLength() + " nodes");
//    System.out.println(nodes.item(0).getNodeValue());
    }
    catch(Exception E)
    {
        System.out.println(E);
    }