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by Phillip Pearson.
Original Post: Using XPath with namespaced documents in dom4j
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In dom4j, once you have parsed a document, you can execute XPath expressions like so:
List list = doc.selectNodes("/path/to/elements/you/want");
The doc.selectNodes function is a thin wrapper around the jaxen XPath library. This saves you from having to write:
XPath xp = new org.jaxen.dom.Dom4jXPath("/path/to/elements/you/want");
List list = xp.execute(doc);
However, if the document uses namespaces, you have to tell jaxen about them, or you won't have any way of specifying namespaced elements. Until yesterday, I thought the only way to do this was:
XPath xp = new org.jaxen.dom.Dom4jXPath("/x:path/x:to/x:elements/x:you/x:want");
xp.addNamespace("x", "http://example.org/some-random-namespace");
List list = xp.execute(doc);
This is a pain in the ass - three lines of code every time you want to use XPath! I did it this way for a little while, but finally got sick of it yesterday and dug through the dom4j code until eventually finding out how to do it properly:
Map namespaces = new TreeMap();
namespaces.put("x", "http://example.org/some-random-namespace");
DocumentFactory.getInstance().setXPathNamespaceURIs(namespaces);
From then on, any time you call selectNodes on a dom4j Node object, you'll be able to use the x: namespace prefix. Much nicer!
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