Evaluvate XPath expression from an element in VTD XML - vtd-xml

Question

XML File:
<apps>
<app name="google">
<branches>
<branch location="us">
<datacenters>
<datacenter city="Mayes County" />
<datacenter city="Douglas County" />
</datacenters>
</branch>
</branches>
</app>
<app name="facebook">
</app>
</apps>
Java Code:
XPath xpath = XPathFactory.newInstance().newXPath();
Document document = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(file);
String expression = "/apps/app[name='google']";
Element element = xpath.evaluvate(expression,document.getDocumentElement();
Element app = (Element)xpath.evaluvate(expression,element,XPathConstants.NODE);
I can able to store the app element and execute the xpath expression within the app element . Like this
xpath.evaluvate("branches/branch[#location='us']",app,XPathConstants.STRING);
How can I do this in VTD XML?

Answer 1

I think you can learn the API by visiting VTD-XML's sourceforge web site. Below is what I think how it will look like:
VTDGen vg = new VTDGen();
String filename ="this.xml";
if (vg.parseFile(filename, true)){
VTDNav vn = vg.getNav();
AutoPilot ap = new AutoPilot(vn);
ap.selectXPath("/apps/app[name='google']");
int i=-1;
while((i=ap.evalXPath())!=-1){
//do something with i, it is the node index
}
}