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POUsing Xpath to get XML in Java trouble with namespaces
 

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  1. POUsing Xpath to get XML in Java trouble with namespaces
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    <p>I'm having trouble extracting XML nodes using Xpath in Java. Here is the URL for the YouTube feed I am using</p> <p><a href="http://gdata.youtube.com/feeds/api/videos?q=skateboarding+dog&amp;start-index=21&amp;max-results=10&amp;v=2" rel="nofollow">http://gdata.youtube.com/feeds/api/videos?q=skateboarding+dog&amp;start-index=21&amp;max-results=10&amp;v=2</a></p> <p>Here's an extract of the feed</p> <pre><code>&lt;?xml version="1.0" encoding="UTF-8" ?&gt; - &lt;feed xmlns="http://www.w3.org/2005/Atom" xmlns:app="http://www.w3.org/2007/app" xmlns:media="http://search.yahoo.com/mrss/" xmlns:openSearch="http://a9.com/-/spec/opensearch/1.1/" xmlns:gd="http://schemas.google.com/g/2005" xmlns:yt="http://gdata.youtube.com/schemas/2007" gd:etag="W/"CEANQ3o9fCp7I2A9WhBbFEg.""&gt; &lt;id&gt;tag:youtube.com,2008:videos&lt;/id&gt; &lt;updated&gt;2013-05-13T13:46:32.464Z&lt;/updated&gt; &lt;category scheme="http://schemas.google.com/g/2005#kind" term="http://gdata.youtube.com/schemas/2007#video" /&gt; &lt;title&gt;Videos matching: skateboarding dog&lt;/title&gt; &lt;logo&gt;http://www.youtube.com/img/pic_youtubelogo_123x63.gif&lt;/logo&gt; &lt;link rel="alternate" type="text/html" href="http://www.youtube.com" /&gt; &lt;link rel="http://schemas.google.com/g/2005#feed" type="application/atom+xml" href="http://gdata.youtube.com/feeds/api/videos?v=2" /&gt; &lt;link rel="http://schemas.google.com/g/2005#batch" type="application/atom+xml" href="http://gdata.youtube.com/feeds/api/videos/batch?v=2" /&gt; &lt;link rel="self" type="application/atom+xml" href="http://gdata.youtube.com/feeds/api/videos?q=skateboarding+dog&amp;start-index=21&amp;max-results=10&amp;v=2" /&gt; &lt;link rel="service" type="application/atomsvc+xml" href="http://gdata.youtube.com/feeds/api/videos?alt=atom-service&amp;v=2" /&gt; &lt;link rel="previous" type="application/atom+xml" href="http://gdata.youtube.com/feeds/api/videos?q=skateboarding+dog&amp;start-index=11&amp;max-results=10&amp;v=2" /&gt; &lt;link rel="next" type="application/atom+xml" href="http://gdata.youtube.com/feeds/api/videos?q=skateboarding+dog&amp;start-index=31&amp;max-results=10&amp;v=2" /&gt; + &lt;author&gt; &lt;name&gt;YouTube&lt;/name&gt; &lt;uri&gt;http://www.youtube.com/&lt;/uri&gt; &lt;/author&gt; &lt;generator version="2.1" uri="http://gdata.youtube.com"&gt;YouTube data API&lt;/generator&gt; &lt;openSearch:totalResults&gt;277515&lt;/openSearch:totalResults&gt; </code></pre> <p>I have created a NamespaceContext class</p> <pre><code>import java.util.Iterator; import javax.xml.XMLConstants; import javax.xml.namespace.NamespaceContext; public class YouTubeNameSpaceContext implements NamespaceContext { @Override public String getNamespaceURI(String prefix) { if (prefix == null) throw new NullPointerException("Invalid Namespace Prefix"); else if (prefix.equals(XMLConstants.DEFAULT_NS_PREFIX)) return "http://www.w3.org/2005/Atom"; else if ("app".equals(prefix)) return "http://www.w3.org/2007/app"; else if ("media".equals(prefix)) return "http://search.yahoo.com/mrss/"; else if ("openSearch".equals(prefix)) return "http://a9.com/-/spec/opensearch/1.1/"; else if ("gd".equals(prefix)) return "http://schemas.google.com/g/2005"; else if ("yt".equals(prefix)) return "http://gdata.youtube.com/schemas/2007"; else return XMLConstants.NULL_NS_URI; } @Override public String getPrefix(String arg0) { // TODO Auto-generated method stub return null; } @Override public Iterator getPrefixes(String arg0) { // TODO Auto-generated method stub return null; } </code></pre> <p>}</p> <p>The Java which I'm using to get the XML node. THe node I'm trying to get is but the result is always 'null' :( </p> <pre><code>XPath xPath = XPathFactory.newInstance().newXPath(); xPath.setNamespaceContext(new YouTubeNameSpaceContext()); String QUERY_FORM_NUMBER = "//feed/openSearch:totalResults"; Node result = (Node)xPath.evaluate(QUERY_FORM_NUMBER, document, XPathConstants.NODE); </code></pre>
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    1. COWhy do you think you only need to implement `getNamespaceURI()` and not `getPrefix()`?
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    2. COAlso: what namespace does `feed` belong to, and why aren't you referencing that in your XPath?
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    3. COHmmm I only implemented `getNamespaceURI()` and not `GetPrefix()` because I was following this example http://stackoverflow.com/questions/5465840/xpath-xml-namespaces-and-java, but I don't 100% understand it. The `feed` node is the root node it doesn't belong to any namespace, does it? (XML isn't my speciality so I don't really know..). Do I need to implement getPrefix?
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