php - Using Java to parse XML

Question

I have made a PHP script that parses an XML file. This is not easy to use and I wanted to implement it in Java.

Inside the first element there are various count of wfs:member elements I loop through:

foreach ($data->children("wfs", true)->member as $member) { }

This was easy to do with Java:

NodeList wfsMember = doc.getElementsByTagName("wfs:member");
for(int i = 0; i < wfsMember.getLength(); i++) { }

I have opened the XML file like this

DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
Document doc = documentBuilder.parse(WeatherDatabaseUpdater.class.getResourceAsStream("wfs.xml"));

Then I need to get a attribute from an element called observerdProperty. In PHP this is simple:

$member->
    children("omso", true)->PointTimeSeriesObservation->
    children("om", true)->observedProperty->
    attributes("xlink", true)->href

But in Java, how do I do this? Do I need to use getElementsByTagName and loop through them if I want to go deeper in the structure?`

In PHP the whole script looks the following.

foreach ($data->children("wfs", true)->member as $member) {
    $dataType = $dataTypes[(string) $member->
                    children("omso", true)->PointTimeSeriesObservation->
                    children("om", true)->observedProperty->
                    attributes("xlink", true)->href];

    foreach ($member->
            children("omso", true)->PointTimeSeriesObservation->
            children("om", true)->result->
            children("wml2", true)->MeasurementTimeseries->
            children("wml2", true)->point as $point) {

        $time = $point->children("wml2", true)->MeasurementTVP->children("wml2", true)->time;
        $value = $point->children("wml2", true)->MeasurementTVP->children("wml2", true)->value;

        $data[$dataType][] = array($time, $value)
    }
}

In the second foreach I loop through the observation elements and get the time and value data from it. Then I save it in an array. If I need to loop through the elements in Java the way I described, this is very hard to implement. I don't think that is the case, so could someone advice me how to implement something similar in Java?

Answer 1

The easiest way, if performance is not a main concern, is probably XPath. With XPath, you can find nodes and attributes simply by specifying a path.

XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath = xPathfactory.newXPath();
XPathExpression expr = xpath.compile(<xpath_expression>);
NodeList nl = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);

The xpath_expression could be as simple as

"string(//member/observedProperty/@href)"

For more information about XPath, XPath Tutorial from W3Schools is pretty good.