Namespace for prefix 'xsi' has not been declared

I'm new into java and xml parsing processes, so i got stucked. My xml is:

  <?xml version="1.0" encoding="utf-16"?>
<LauncherInfo xmlns:xsi="http://ift.tt/ra1lAU" xmlns:xsd="http://ift.tt/tphNwY" xmlns="http://ift.tt/1vC7NUZ" hash="d8bf41f6053ab2df28704dfcda443f9199546d3b">
  <File Name="parakstitais.edoc" Location="vieta_kur_saglabat" />
  <Action xsi:type="CreateNewSignAction">
    <FileReferences>
        <FileReference Name="Document1.doc" Address="some url" />
        <FileReference Name="Scan7.pdf" Address="some url" />
        <FileReference Name="Scan8.pdf" Address="some url" />
    </FileReferences>
  </Action>
</LauncherInfo>

and my goal is to extract all Action part, so it should be like:

<Action xsi:type="CreateNewSignAction">
    <FileReferences>
        <FileReference Name="Document1.doc" Address="some url" />
        <FileReference Name="Scan7.pdf" Address="some url" />
        <FileReference Name="Scan8.pdf" Address="some url" />
    </FileReferences>
  </Action>

Currently my Java code is

public static void main(String[] args) throws ParserConfigurationException,
        MalformedURLException, SAXException, IOException,
        TransformerException, XPathExpressionException {

    String URL = "my xml URL";
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
    factory.setNamespaceAware(false);

    DocumentBuilder builder = factory.newDocumentBuilder();
    Document doc = builder.parse(new URL(URL).openStream());

     URL namespaceURL = new URL("http://ift.tt/ra1lAU");
        String namespace = "xmlns:xsi="+namespaceURL.toString();

        Element messages = doc.createElementNS(namespace, "messages");
        doc.appendChild(messages);

    XPath xPath = XPathFactory.newInstance().newXPath();


    Node result = (Node) xPath.evaluate("LauncherInfo/Action", doc,
            XPathConstants.NODE);

    System.out.println(nodeToString(result));
    System.out.println("...");
}

private static String nodeToString(Node node) throws TransformerException {
    StringWriter buf = new StringWriter();
    Transformer xform = TransformerFactory.newInstance().newTransformer();
    xform.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
    xform.transform(new DOMSource(node), new StreamResult(buf));
    return (buf.toString());
}

When launching an error appears: ERROR: 'Namespace for prefix 'xsi' has not been declared.'. I suppose that something with namespace declaration should be done. Is there any way to declare namepace URI in xpath query, or there is a better solution?