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<?xml version="1.0" encoding="UTF-8"?>
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<!--
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Copyright 2003-2005 Sun Microsystems, Inc. All Rights Reserved.
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DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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This code is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License version 2 only, as
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published by the Free Software Foundation. Sun designates this
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particular file as subject to the "Classpath" exception as provided
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by Sun in the LICENSE file that accompanied this code.
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This code is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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version 2 for more details (a copy is included in the LICENSE file that
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accompanied this code).
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You should have received a copy of the GNU General Public License version
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2 along with this work; if not, write to the Free Software Foundation,
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Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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CA 95054 USA or visit www.sun.com if you need additional information or
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have any questions.
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-->
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<title>javax.xml.xpath</title>
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<meta name="@author" content="mailto:Ben@galbraiths.org" />
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<meta name="@author" content="mailto:Norman.Walsh@Sun.com" />
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<meta name="@author" content="mailto:Jeff.Suttor@Sun.com" />
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<meta name="@version" content="$Revision: 1.3 $, $Date: 2005/11/03 19:34:17 $" />
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<meta name="@see" content="http://www.w3.org/TR/xpath" />
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<meta name="@since" content="1.5" />
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</head>
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<body>
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<p>This package provides an <em>object-model neutral</em> API for the
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evaluation of XPath expressions and access to the evaluation
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environment.
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</p>
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<p>The following XML standards apply:</p>
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<ul>
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<li><a href="http://www.w3.org/TR/xpath">XML Path Language (XPath) Version 1.0</a></li>
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</ul>
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<hr />
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<h2>XPath Overview</h2>
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<p>The XPath language provides a simple, concise syntax for selecting
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nodes from an XML document. XPath also provides rules for converting a
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node in an XML document object model (DOM) tree to a boolean, double,
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or string value. XPath is a W3C-defined language and an official W3C
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recommendation; the W3C hosts the XML Path Language (XPath) Version
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1.0 specification.
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</p>
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<p>XPath started in life in 1999 as a supplement to the XSLT and
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XPointer languages, but has more recently become popular as a
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stand-alone language, as a single XPath expression can be used to
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replace many lines of DOM API code.
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</p>
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<h3>XPath Expressions</h3>
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<p>An XPath <em>expression</em> is composed of a <em>location
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path</em> and one or more optional <em>predicates</em>. Expressions
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may also include XPath variables.
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</p>
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<p>The following is an example of a simple XPath expression:</p>
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<pre>
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/foo/bar
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</pre>
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<p>This example would select the <code><bar></code> element in
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an XML document such as the following:</p>
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<pre>
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<foo>
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<bar/>
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</foo>
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</pre>
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<p>The expression <code>/foo/bar</code> is an example of a location
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path. While XPath location paths resemble Unix-style file system
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paths, an important distinction is that XPath expressions return
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<em>all</em> nodes that match the expression. Thus, all three
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<code><bar></code> elements in the following document would be
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selected by the <code>/foo/bar</code> expression:</p>
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<pre>
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<foo>
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<bar/>
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<bar/>
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<bar/>
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</foo>
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</pre>
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<p>A special location path operator, <code>//</code>, selects nodes at
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any depth in an XML document. The following example selects all
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<code><bar></code> elements regardless of their location in a
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document:</p>
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<pre>
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//bar
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</pre>
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<p>A wildcard operator, *, causes all element nodes to be selected.
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The following example selects all children elements of a
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<code><foo></code> element:</p>
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<pre>
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/foo/*
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</pre>
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<p>In addition to element nodes, XPath location paths may also address
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attribute nodes, text nodes, comment nodes, and processing instruction
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nodes. The following table gives examples of location paths for each
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of these node types:</p>
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<table border="1">
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<tr>
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<td>Location Path</td>
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<td>Description</td>
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</tr>
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<tr>
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<td>
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<code>/foo/bar/<strong>@id</strong></code>
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</td>
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<td>Selects the attribute <code>id</code> of the <code><bar></code> element
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</td>
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</tr>
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<tr>
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<td><code>/foo/bar/<strong>text()</strong></code>
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</td>
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<td>Selects the text nodes of the <code><bar></code> element. No
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distinction is made between escaped and non-escaped character data.
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</td>
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</tr>
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<tr>
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<td><code>/foo/bar/<strong>comment()</strong></code>
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</td>
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<td>Selects all comment nodes contained in the <code><bar></code> element.
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</td>
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</tr>
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<tr>
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<td><code>/foo/bar/<strong>processing-instruction()</strong></code>
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</td>
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<td>Selects all processing-instruction nodes contained in the
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<code><bar></code> element.
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</td>
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</tr>
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</table>
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<p>Predicates allow for refining the nodes selected by an XPath
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location path. Predicates are of the form
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<code>[<em>expression</em>]</code>. The following example selects all
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<code><foo></code> elements that contain an <code>include</code>
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attribute with the value of <code>true</code>:</p>
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<pre>
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//foo[@include='true']
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</pre>
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<p>Predicates may be appended to each other to further refine an
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expression, such as:</p>
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<pre>
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//foo[@include='true'][@mode='bar']
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</pre>
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<h3>Using the XPath API</h3>
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<p>
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The following example demonstrates using the XPath API to select one
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or more nodes from an XML document:</p>
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<pre>
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XPath xpath = XPathFactory.newInstance().newXPath();
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String expression = "/widgets/widget";
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InputSource inputSource = new InputSource("widgets.xml");
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NodeList nodes = (NodeList) xpath.evaluate(expression, inputSource, XPathConstants.NODESET);
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</pre>
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<h3>XPath Expressions and Types</h3>
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<p>While XPath expressions select nodes in the XML document, the XPath
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API allows the selected nodes to be coalesced into one of the
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following other data types:</p>
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<ul>
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<li><code>Boolean</code></li>
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<li><code>Number</code></li>
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<li><code>String</code></li>
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</ul>
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<p>The desired return type is specified by a {@link
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javax.xml.namespace.QName} parameter in method call used to evaluate
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the expression, which is either a call to
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<code>XPathExpression.evalute(...)</code> or to one of the
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<code>XPath.evaluate(...)</code> convenience methods. The allowed
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QName values are specified as constants in the {@link
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javax.xml.xpath.XPathConstants} class; they are:</p>
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<ul>
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<li>{@link javax.xml.xpath.XPathConstants#NODESET}</li>
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<li>{@link javax.xml.xpath.XPathConstants#NODE}</li>
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<li>{@link javax.xml.xpath.XPathConstants#STRING}</li>
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<li>{@link javax.xml.xpath.XPathConstants#BOOLEAN}</li>
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<li>{@link javax.xml.xpath.XPathConstants#NUMBER}</li>
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</ul>
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<p>When a <code>Boolean</code> return type is requested,
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<code>Boolean.TRUE</code> is returned if one or more nodes were
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selected; otherwise, <code>Boolean.FALSE</code> is returned.</p>
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<p>The <code>String</code> return type is a convenience for retrieving
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the character data from a text node, attribute node, comment node, or
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processing-instruction node. When used on an element node, the value
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of the child text nodes is returned.
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</p>
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<p>The <code>Number</code> return type attempts to coalesce the text
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of a node to a <code>double</code> data type.
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</p>
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<h3>XPath Context</h3>
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<p>XPath location paths may be relative to a particular node in the
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document, known as the <code>context</code>. Consider the following
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XML document:</p>
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<pre>
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<widgets>
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<widget>
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<manufacturer/>
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<dimensions/>
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</widget>
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</widgets>
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</pre>
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<p>The <code><widget></code> element can be selected with the
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following XPath API code:</p>
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<pre>
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// parse the XML as a W3C Document
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DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
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Document document = builder.parse(new File("/widgets.xml"));
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XPath xpath = XPathFactory.newInstance().newXPath();
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String expression = "/widgets/widget";
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Node widgetNode = (Node) xpath.evaluate(expression, document, XPathConstants.NODE);
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</pre>
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<p>With a reference to the <code><widget></code> element, a
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relative XPath expression can now written to select the
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<code><manufacturer></code> child element:</p>
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<pre>
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XPath xpath = XPathFactory.newInstance().newXPath();
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<strong>String expression = "manufacturer";</strong>
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Node manufacturerNode = (Node) xpath.evaluate(expression, <strong>widgetNode</strong>, XPathConstants.NODE);
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</pre>
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<ul>
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<li>Author <a href="mailto:Ben@galbraiths.org">Ben Galbraith</a></li>
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<li>Author <a href="mailto:Norman.Walsh@Sun.com">Norman Walsh</a></li>
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<li>Author <a href="mailto:Jeff.Suttor@Sun.com">Jeff Suttor</a></li>
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<li>See <a href="http://www.w3.org/TR/xpath">XML Path Language (XPath) Version 1.0</a></li>
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<li>Since 1.5</li>
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</ul>
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</body>
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</html>
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