how to use XPATH process DOM node on ANDORID?

Question

Hi folks,

I am in a ANDROID project that use XPATH a lot. I followed the way in The Force Unleashed: XML+XPath On Android Using Dom4j And Jaxen. Everything's fine beside the performance. The XML file's big and read intensively. Following code consume 6 mins.

org.dom4j.Document MatrixXML = (new org.dom4j.io.SAXReader()).read(this.getResources().getAssets().open(XMLFile));

for (int i = 0; i < ListUsedQuestions.size(); i++) {
 aQuestion = ListUsedQuestions.get(i);
 List DxList = new ArrayList<Node>();
 DxList = MatrixXML.selectNodes("/diagnoses/diagnosis[question[@id='" + aQuestion.getQuestionID() + "' and @weighting < 0]and not(@triggersystemid='" + systemID + "')]");
}

I think it is worth to try DOM since it store all XML file in the memory. I tried following code but the last line has a error:

org.w3c.dom.Document doc = javax.xml.parsers.DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(this.getResources().getAssets().open(XMLFile));

DOMXPath xpath = new DOMXPath("/xpath.......");

List DxList = xpath.selectNodes((Node)doc.getDocumentElement());   <--- ERROR

Can anyone have any suggestion for me in this situation?

Thanks guys.