Multiple NameSpace in Xml Xpath value

Am new in using Xpath parsing in Java for Xmls. But I learnt it and it worked pretty well until this below issue am not sure how to go traverse to next node in this . Please find the below code and Let me know what needs to be corrected .

package test;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.TransformerException;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;

import org.w3c.dom.Document;
import org.w3c.dom.NodeList;

public class CallTestcall {
    public static void main(String[] args) throws Exception {

        DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
        domFactory.setNamespaceAware(true);
        DocumentBuilder builder = domFactory.newDocumentBuilder();

        String responsePath1 = "C:/Verizon/webserviceTestTool/generatedResponse/example.xml";
        Document doc1 = builder.parse(responsePath1);

        String responsePath0 = "C:/Verizon/webserviceTestTool/generatedResponse/response.xml";
        Document doc0 = builder.parse(responsePath0);

        example0(doc0);
        example1(doc1);
    }

    private static void example0(Document example)
            throws XPathExpressionException, TransformerException {
        System.out.println("\n*** First example - namespacelookup hardcoded ***");

        XPath xPath = XPathFactory.newInstance().newXPath();
        xPath.setNamespaceContext(new HardcodedNamespaceResolver());


        String result = xPath.evaluate("s:Envelope/s:Body/ns1:UpdateSessionResponse",
                example);

        // I tried all the Values to traverse further to UpdateSessionResult but am not able to I used the following xpath expressions

        result = xPath.evaluate("s:Envelope/s:Body/ns1:UpdateSessionResponse/a:UpdateSessionResult",
                example);

        result = xPath.evaluate("s:Envelope/s:Body/ns1:UpdateSessionResponse/i:UpdateSessionResult",
                example);

        System.out.println("example0 : "+result);
    }

    private static void example1(Document example)
            throws XPathExpressionException, TransformerException {
        System.out.println("\n*** First example - namespacelookup hardcoded ***");

        XPath xPath = XPathFactory.newInstance().newXPath();
        xPath.setNamespaceContext(new HardcodedNamespaceResolver());

        String result = xPath.evaluate("books:booklist/technical:book/:author",
                example);
        System.out.println("example1 : "+result);
    }

}

Please find the class that implements nameSpaceContext where I have added the prefixes

package test;

import java.util.Iterator;
import javax.xml.XMLConstants;
import javax.xml.namespace.NamespaceContext;

public class HardcodedNamespaceResolver implements NamespaceContext {



/**
     * This method returns the uri for all prefixes needed. Wherever possible it
     * uses XMLConstants.
     * 
     * @param prefix
     * @return uri
     */
    public String getNamespaceURI(String prefix) {
        if (prefix == null) {
            throw new IllegalArgumentException("No prefix provided!");
        } else if (prefix.equals(XMLConstants.DEFAULT_NS_PREFIX)) {
            return "http://univNaSpResolver/book";
        } else if (prefix.equals("books")) {
            return "http://univNaSpResolver/booklist";
        } else if (prefix.equals("fiction")) {
            return "http://univNaSpResolver/fictionbook";
        } else if (prefix.equals("technical")) {
            return "http://univNaSpResolver/sciencebook";
        } else if (prefix.equals("s")) {
            return "http://schemas.xmlsoap.org/soap/envelope/";
        } else if (prefix.equals("a")) {
            return "http://channelsales.corp.cox.com/vzw/v1/data/";
        } else if (prefix.equals("i")) {
            return "http://www.w3.org/2001/XMLSchema-instance";
        } else if (prefix.equals("ns1")) {
            return "http://channelsales.corp.cox.com/vzw/v1/";
        } 


        else {
            return XMLConstants.NULL_NS_URI;
        }
    }

    public String getPrefix(String namespaceURI) {
        // Not needed in this context.
        return null;
    }

    public Iterator getPrefixes(String namespaceURI) {
        // Not needed in this context.
        return null;
    }

}

Please find my Xml ::::

String XmlString  = "<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"><s:Body><UpdateSessionResponse xmlns="http://channelsales.corp.cox.com/vzw/v1/"><UpdateSessionResult xmlns:a="http://channelsales.corp.cox.com/vzw/v1/data/" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
<a:ResponseHeader>
<a:SuccessFlag>true</a:SuccessFlag>
<a:ErrorCode i:nil="true"/>
<a:ErrorMessage i:nil="true"/>
<a:Timestamp>2012-12-05T15:28:35.5363903-05:00</a:Timestamp>
</a:ResponseHeader>
<a:SessionId>cd3ce09e-eb33-48e8-b628-ecd406698aee</a:SessionId>
<a:CacheKey i:nil="true"/>