Fetch XML-Nodes by Path

Question

I have following (very large => 5GB) XML:

<Hotels>
  <Hotel>
    <Name>Hotel 1</Name>
    <City>City 1</City>
    <Phone>12345</Phone>
  </Hotel>
  <Hotel>
    <Name>Hotel 2</Name>
    <City>City 2</City>
    <Phone>67890</Phone>
  </Hotel>
  ...
</Hotels>

And I have a file which defines which fields I want to extract and what their path is:

$root = "/Hotels/Hotel";
$fields = array("HotelName"   => "/Name",
                "PhoneNumber" => "/Phone");

So the path for HotelName would be: /Hotels/Hotel/Name.

Now I want to get the information for every hotel. I cannot create classes for them (like here) because the script has to be dynamically and different XML-files with different definition-files will be passed.

How can I solve this by using the paths, without classes and with low memory usage (=> large files)?

//Edit: Everything is implemented. I just need a way to iterate through the Hotel and get their values with the paths I have.

Answer 1

Try reading this tutorial there are some explanations and examples. http://viralpatel.net/blogs/java-xml-xpath-tutorial-parse-xml/

For your porpuse you shoudl use something from Stax familiy, not DOM.

try do this

public class QueryXML {
  public void query() throws ParserConfigurationException, SAXException,
      IOException, XPathExpressionException {
    // standard for reading an XML file
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
    factory.setNamespaceAware(true);
    DocumentBuilder builder;
    Document doc = null;
    XPathExpression expr = null;
    builder = factory.newDocumentBuilder();
    doc = builder.parse("person.xml");

    // create an XPathFactory
    XPathFactory xFactory = XPathFactory.newInstance();

    // create an XPath object
    XPath xpath = xFactory.newXPath();

    // compile the XPath expression
    expr = xpath.compile("//person[firstname='Lars']/lastname/text()");
    // run the query and get a nodeset
    Object result = expr.evaluate(doc, XPathConstants.NODESET);

    // cast the result to a DOM NodeList
    NodeList nodes = (NodeList) result;
    for (int i=0; i<nodes.getLength();i++){
      System.out.println(nodes.item(i).getNodeValue());
    }

    // new XPath expression to get the number of people with name Lars
    expr = xpath.compile("count(//person[firstname='Lars'])");
    // run the query and get the number of nodes
    Double number = (Double) expr.evaluate(doc, XPathConstants.NUMBER);
    System.out.println("Number of objects " +number);

    // do we have more than 2 people with name Lars?
    expr = xpath.compile("count(//person[firstname='Lars']) >2");
    // run the query and get the number of nodes
    Boolean check = (Boolean) expr.evaluate(doc, XPathConstants.BOOLEAN);
    System.out.println(check);
  }

You can simply adapt that code to your needs.

Answer 2

If you already found the <Hotel/> node and got it as a DOM-reference, just access its children (with the hotel as context). Either using

• XPath: ./Name or shorter Name (just don't start it with /, which refers to the root), but make sure to use the hotel node as query context; or
• DOM: hotel.getChildNodes(), and then loop over the result set comparing element names to find the respective child node.