XML Parsing with STAX API

Question

I am trying to parse XML Structure of Open Street Maps using Stax. In my implementation I use XMLStreamConstants.START_ELEMENT and XMLStreamConstants.END_ELEMENT to recognize Elements.

OpenStreetMaps structure has Elements such as tag which describe as well the node, as well as the way. Here is an example of the structure:

      <node id="2311741639" ... lat="50.7756648" lon="6.0844948">
       <tag k="entrance" v="yes"/>
      </node>
      <way id="4964449" visible="true" ... uid="67862">
       <nd ref="27290865"/>
        ...
       <tag k="highway" v="residential"/>
        ...
      </way>

How can I distinguish between node and way if parser reads Tag-Element?

Answer 1

You could use an ArrayDeque of your node representations, or even build a temporary DOM-like structure if the depth of your hierarchy is small.

Here's an example with ArrayDeque...

Assuming this XML file named stuff.xml:

<?xml version="1.0" encoding="UTF-8"?>

<stuff>

<node id="2311741639" lat="50.7756648" lon="6.0844948">
    <tag k="entrance" v="yes"/>
</node>

<way id="4964449" visible="true" uid="67862">
    <nd ref="27290865"/>
    <tag k="highway" v="residential"/>
</way>

</stuff>

Assuming the file is on path: /my/path/

Here is the code (try/catch Java 6 style):

InputStream is = null;
XMLStreamReader reader = null;
try {
    is = new FileInputStream(new File("/my/path/stuff.xml"));
    XMLInputFactory xif = XMLInputFactory.newInstance();
    reader = xif.createXMLStreamReader(is);
    ArrayDeque<String> nodes = new ArrayDeque<String>();
    while (reader.hasNext()) {
        int current = reader.next();
        switch (current) {
            case XMLStreamConstants.START_ELEMENT: {
                nodes.add(reader.getLocalName());
                System.out.println("START: " + nodes.getLast());
                if (nodes.size() > 1) {
                    Iterator<String> iterator = nodes.descendingIterator();
                    // skipping first one as it's already represented
                    iterator.next();
                    while (iterator.hasNext()) {
                        System.out.println("\t in " + iterator.next());
                    }
                }
                break;
            }
            case XMLStreamConstants.END_ELEMENT: {
                System.out.println("END: " + nodes.removeLast());
                Iterator<String> iterator = nodes.descendingIterator();
                while (iterator.hasNext()) {
                    System.out.println("\t in " + iterator.next());
                }
                break;
            }
        }
    }

}
        catch (FileNotFoundException fnfe) {
            fnfe.printStackTrace();
        }
        catch (XMLStreamException xse) {
            xse.printStackTrace();
        }
        finally {
            if (reader != null) {
                try {
                    reader.close();
                    is.close();
                }
                catch (XMLStreamException xse) {
                    xse.printStackTrace();
                }
                catch (IOException ioe) {
                    ioe.printStackTrace();
                }
            }
        }

Output:

START: stuff
START: node
     in stuff
START: tag
     in node
     in stuff
END: tag
     in node
     in stuff
END: node
     in stuff
START: way
     in stuff
START: nd
     in way
     in stuff
END: nd
     in way
     in stuff
START: tag
     in way
     in stuff
END: tag
     in way
     in stuff
END: way
     in stuff
END: stuff