how to retrieve XML data using XPath which has a default namespace in Java?

Question

I've come across and problem that I've looked up on stack overflow but none of the solutions seems to solve the problem for me.

I'm retrieving XML data from Yahoo and it comes back as below (truncated for brevity's sake).

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<fantasy_content xmlns="http://fantasysports.yahooapis.com/fantasy/v2/base.rng" xmlns:yahoo="http://www.yahooapis.com/v1/base.rng" copyright="Data provided by Yahoo! and STATS, LLC" refresh_rate="31" time="55.814027786255ms" xml:lang="en-US" yahoo:uri="http://fantasysports.yahooapis.com/fantasy/v2/league/328.l.108462/settings">
    <league>
        <league_key>328.l.108462</league_key>
        <league_id>108462</league_id>
        <draft_status>postdraft</draft_status>
    </league>
</fantasy_content>

I've been having a problem getting XPath to retrieve any elements so I've written a unit test to try to resolve it and it looks like:

    final File file = new File("league-settings.xml");
    javax.xml.parsers.DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
    dbFactory.setNamespaceAware(true);
    javax.xml.parsers.DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
    org.w3c.dom.Document doc = dBuilder.parse(file);
    javax.xml.xpath.XPath xPath = XPathFactory.newInstance().newXPath();
    xPath.setNamespaceContext(new YahooNamespaceContext());
    final String expression = "yfs:league";
    final XPathExpression expr = xPath.compile(expression);
    Object nodes = expr.evaluate(doc, XPathConstants.NODESET);

    assert(nodes instanceof NodeList);
    NodeList leagueNodes = (NodeList)nodes;
    int leaguesLength = leagueNodes.getLength();
    assertEquals(leaguesLength, 1);

The YahooNamespaceContext class I created to map the namespaces looks as follows:

public class YahooNamespaceContext implements NamespaceContext {
    public static final String YAHOO_NS = "http://www.yahooapis.com/v1/base.rng";
    public static final String DEFAULT_NS = "http://fantasysports.yahooapis.com/fantasy/v2/base.rng";
    public static final String YAHOO_PREFIX = "yahoo";
    public static final String DEFAULT_PREFIX = "yfs";

    private final Map<String, String> namespaceMap = new HashMap<String, String>();
    public YahooNamespaceContext() {
        namespaceMap.put(DEFAULT_PREFIX, DEFAULT_NS);
        namespaceMap.put(YAHOO_PREFIX, YAHOO_NS);
    }

    public String getNamespaceURI(String prefix) {
        return namespaceMap.get(prefix);
    }

    public String getPrefix(String uri) {
        throw new UnsupportedOperationException();
    }

    public Iterator<String> getPrefixes(String uri) {
        throw new UnsupportedOperationException();
    }

}

Any help with people with more experience with XML namespaces or debugging tips into Xpath compilation/evaluation would be appreciated.

What is the result you're expecting from this code, and what is the result you're actually getting? Or in other words, what is the question? — LarsH
– LarsH, Commented Sep 16, 2014 at 20:10

LarsH · Accepted Answer · 2014-09-16 20:27:46Z

2

If the problem is that you're getting zero as the length of the result nodelist, have you tried changing

final String expression = "yfs:league";

to

final String expression = "//yfs:league";

?

It appears that the context for evaluating your XPath expressions, doc, is the root node of the document. dBuilder.parse(file) returns the document root node, not the outermost element (a.k.a. document element). Remember, in XPath, a root node is not an element. So doc is not the yfs:fantasy_content element node but is its (invisible) parent.

In that context, the XPath expression "yfs:league" will only select an element that is a direct child of that root node, of which there is no yfs:league -- only yfs:fantasy_content.

edited Sep 16, 2014 at 20:27

answered Sep 16, 2014 at 20:13

LarsH

28.1k9 gold badges99 silver badges162 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

sparky Over a year ago

that did the trick. Some documentation I read indicated that // was from the root of the node but I guess that's incorrect. Thanks

LarsH Over a year ago

@spark: It's true that an XPath expression beginning with // will be evaluated starting from the root node of the document, regardless of the current context node.

LarsH · Accepted Answer · 2014-09-16 20:17:27Z

1

The XPath expression yfs:league is equivalent to child::yfs:league. It means: find direct children nodes (not descendants) of doc with the specified local name (league) and namespace URI (http://fantasysports.yahooapis.com/fantasy/v2/base.rng).

You must take into account the outermost element (fantasy_content) or search for descendant instead of child nodes.

Replacing

final String expression = "yfs:league";

with

final String expression = "yfs:fantasy_content/yfs:league";

or with

final String expression = "//yfs:league";

will solve the problem.

edited Sep 16, 2014 at 20:17

LarsH

28.1k9 gold badges99 silver badges162 bronze badges

answered Sep 16, 2014 at 20:15

Aldo

5593 silver badges15 bronze badges

Collectives™ on Stack Overflow

how to retrieve XML data using XPath which has a default namespace in Java?

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related