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PORunning XPath on child node
 

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    <p>I'm trying to do a xpath lookup on nodes returned by xpath lookup, but it doesn't seem to work as I expected.XPaths executed on the child nodes of a document seem to be executd against hthe root node of the document (in the example, the inventory tag.), instead of the root of the provided node.</p> <p>Am I missing something here? I'm new to XPath.</p> <p>Also, please don't answer "just do //book[author='Neal Stephenson'/title". I have a legitimate use case, and this is a simplified example.</p> <p>Code snippet</p> <pre><code>DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance(); domFactory.setNamespaceAware(true); DocumentBuilder builder = domFactory.newDocumentBuilder(); Document doc = builder.parse("src/main/java/books.xml"); XPathFactory factory = XPathFactory.newInstance(); XPath xpath = factory.newXPath(); Node book = (Node) xpath.evaluate("//book[author='Neal Stephenson']", doc, XPathConstants.NODE); Node title = (Node) xpath.evaluate("/title", book, XPathConstants.NODE); // I get null here. Node inventory = (Node) xpath.evaluate("/inventory", book, XPathConstants.NODE); // this returns a node. </code></pre> <p>book.xml</p> <pre><code>&lt;inventory&gt; &lt;book year="2000"&gt; &lt;title&gt;Snow Crash&lt;/title&gt; &lt;author&gt;Neal Stephenson&lt;/author&gt; &lt;publisher&gt;Spectra&lt;/publisher&gt; &lt;isbn&gt;0553380958&lt;/isbn&gt; &lt;price&gt;14.95&lt;/price&gt; &lt;/book&gt; &lt;book year="2005"&gt; &lt;title&gt;Burning Tower&lt;/title&gt; &lt;author&gt;Larry Niven&lt;/author&gt; &lt;author&gt;Jerry Pournelle&lt;/author&gt; &lt;publisher&gt;Pocket&lt;/publisher&gt; &lt;isbn&gt;0743416910&lt;/isbn&gt; &lt;price&gt;5.99&lt;/price&gt; &lt;/book&gt; &lt;book year="1995"&gt; &lt;title&gt;Zodiac&lt;/title&gt; &lt;author&gt;Neal Stephenson&lt;/author&gt; &lt;publisher&gt;Spectra&lt;/publisher&gt; &lt;isbn&gt;0553573862&lt;/isbn&gt; &lt;price&gt;7.50&lt;/price&gt; &lt;/book&gt; &lt;!-- more books... --&gt; &lt;/inventory&gt; </code></pre>
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    1. COOthers have provided good answers to your question. Note that `//book` and other expressions beginning with `//` may affect performance, as the entire DOM tree must be searched. `/inventory/book` is more efficient. On the same note, if an XPath expression is going to be used multiple times, you should probably compile it once with `XPath.compile()` and run `XPathExpression.evaluate()` on the result, instead of repeatedly calling `XPath.evaluate()`.
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      1. USmarkusk
    2. COAnswered here : http://stackoverflow.com/questions/8358994/xpath-search-on-subtree
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