jaxp/src/java.xml/share/classes/javax/xml/xpath/package.html - platform/libcore - Git at Google

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 This package provides an <em>object-model neutral</em> API for the
 evaluation of XPath expressions and access to the evaluation
 environment.

 <p>
 The XPath API supports <a href="http://www.w3.org/TR/xpath">
     XML Path Language (XPath) Version 1.0</a>

 <hr />

 <ul>
     <li><a href='#XPath.Overview'>1. XPath Overview</a></li>
     <li><a href='#XPath.Expressions'>2. XPath Expressions</a></li>
     <li><a href='#XPath.Datatypes'>3. XPath Data Types</a>
         <ul>
             <li><a href='#XPath.Datatypes.QName'>3.1 QName Types</a>
             <li><a href='#XPath.Datatypes.Class'>3.2 Class Types</a>
             <li><a href='#XPath.Datatypes.Enum'>3.3 Enum Types</a>
         </ul>
     </li>
     <li><a href='#XPath.Context'>4. XPath Context</a></li>
     <li><a href='#XPath.Use'>5. Using the XPath API</a></li>
 </ul>
 <p>
 <a name="XPath.Overview"></a>
 <h3>1. XPath Overview</h3>

 <p>The XPath language provides a simple, concise syntax for selecting
 nodes from an XML document. XPath also provides rules for converting a
 node in an XML document object model (DOM) tree to a boolean, double,
 or string value. XPath is a W3C-defined language and an official W3C
 recommendation; the W3C hosts the XML Path Language (XPath) Version
 1.0 specification.
 </p>

 <p>XPath started in life in 1999 as a supplement to the XSLT and
 XPointer languages, but has more recently become popular as a
 stand-alone language, as a single XPath expression can be used to
 replace many lines of DOM API code.
 </p>

 <a name="XPath.Expressions"></a>
 <h3>2. XPath Expressions</h3>

 <p>An XPath <em>expression</em> is composed of a <em>location
 path</em> and one or more optional <em>predicates</em>. Expressions
 may also include XPath variables.
 </p>

 <p>The following is an example of a simple XPath expression:</p>

 <blockquote>
 <pre>
 /foo/bar
 </pre>
 </blockquote>

 <p>This example would select the <code>&lt;bar&gt;</code> element in
 an XML document such as the following:</p>

 <blockquote>
 <pre>
 &lt;foo&gt;
     &lt;bar/&gt;
 &lt;/foo&gt;
 </pre>
 </blockquote>

 <p>The expression <code>/foo/bar</code> is an example of a location
 path. While XPath location paths resemble Unix-style file system
 paths, an important distinction is that XPath expressions return
 <em>all</em> nodes that match the expression. Thus, all three
 <code>&lt;bar&gt;</code> elements in the following document would be
 selected by the <code>/foo/bar</code> expression:</p>

 <blockquote>
 <pre>
 &lt;foo&gt;
     &lt;bar/&gt;
     &lt;bar/&gt;
     &lt;bar/&gt;
 &lt;/foo&gt;
 </pre>
 </blockquote>

 <p>A special location path operator, <code>//</code>, selects nodes at
 any depth in an XML document. The following example selects all
 <code>&lt;bar&gt;</code> elements regardless of their location in a
 document:</p>

 <blockquote>
 <pre>
 //bar
 </pre>
 </blockquote>

 <p>A wildcard operator, *, causes all element nodes to be selected.
 The following example selects all children elements of a
 <code>&lt;foo&gt;</code> element:

 <blockquote>
 <pre>
 /foo/*
 </pre>
 </blockquote>

 <p>In addition to element nodes, XPath location paths may also address
 attribute nodes, text nodes, comment nodes, and processing instruction
 nodes. The following table gives examples of location paths for each
 of these node types:</p>

 <table border="1">
 <tr>
 <td>Location Path</td>
 <td>Description</td>
 </tr>
 <tr>
 <td>
 <code>/foo/bar/<strong>@id</strong></code>
 </td>
 <td>Selects the attribute <code>id</code> of the <code>&lt;bar&gt;</code> element
 </td>
 </tr>
 <tr>
 <td><code>/foo/bar/<strong>text()</strong></code>
 </td>
 <td>Selects the text nodes of the <code>&lt;bar&gt;</code> element. No
 distinction is made between escaped and non-escaped character data.
 </td>
 </tr>
 <tr>
 <td><code>/foo/bar/<strong>comment()</strong></code>
 </td>
 <td>Selects all comment nodes contained in the <code>&lt;bar&gt;</code> element.
 </td>
 </tr>
 <tr>
 <td><code>/foo/bar/<strong>processing-instruction()</strong></code>
 </td>
 <td>Selects all processing-instruction nodes contained in the
 <code>&lt;bar&gt;</code> element.
 </td>
 </tr>
 </table>

 <p>Predicates allow for refining the nodes selected by an XPath
 location path. Predicates are of the form
 <code>[<em>expression</em>]</code>. The following example selects all
 <code>&lt;foo&gt;</code> elements that contain an <code>include</code>
 attribute with the value of <code>true</code>:</p>

 <blockquote>
 <pre>
 //foo[@include='true']
 </pre>
 </blockquote>

 <p>Predicates may be appended to each other to further refine an
 expression, such as:</p>

 <blockquote>
 <pre>
 //foo[@include='true'][@mode='bar']
 </pre>
 </blockquote>

 <a name="XPath.Datatypes"></a>
 <h3>3. XPath Data Types</h3>

 <p>While XPath expressions select nodes in the XML document, the XPath
 API allows the selected nodes to be coalesced into one of the
 following data types:</p>

 <ul>
 <li><code>Boolean</code></li>
 <li><code>Number</code></li>
 <li><code>String</code></li>
 </ul>

 <a name="XPath.Datatypes.QName"></a>
 <h3>3.1 QName types</h3>
 The XPath API defines the following {@link javax.xml.namespace.QName} types to
 represent return types of an XPath evaluation:
 <ul>
 <li>{@link javax.xml.xpath.XPathConstants#NODESET}</li>
 <li>{@link javax.xml.xpath.XPathConstants#NODE}</li>
 <li>{@link javax.xml.xpath.XPathConstants#STRING}</li>
 <li>{@link javax.xml.xpath.XPathConstants#BOOLEAN}</li>
 <li>{@link javax.xml.xpath.XPathConstants#NUMBER}</li>
 </ul>

 <p>The return type is specified by a {@link javax.xml.namespace.QName} parameter
 in method call used to evaluate the expression, which is either a call to
 <code>XPathExpression.evalute(...)</code> or <code>XPath.evaluate(...)</code>
 methods.

 <p>When a <code>Boolean</code> return type is requested,
 <code>Boolean.TRUE</code> is returned if one or more nodes were
 selected; otherwise, <code>Boolean.FALSE</code> is returned.

 <p>The <code>String</code> return type is a convenience for retrieving
 the character data from a text node, attribute node, comment node, or
 processing-instruction node. When used on an element node, the value
 of the child text nodes is returned.

 <p>The <code>Number</code> return type attempts to coalesce the text
 of a node to a <code>double</code> data type.

 <a name="XPath.Datatypes.Class"></a>
 <h3>3.2 Class types</h3>
 In addition to the QName types, the XPath API supports the use of Class types
 through the <code>XPathExpression.evaluteExpression(...)</code> or
 <code>XPath.evaluateExpression(...)</code> methods.

 The XPath data types are mapped to Class types as follows:
 <ul>
 <li><code>Boolean</code> -- <code>Boolean.class</code></li>
 <li><code>Number</code> -- <code>Number.class</code></li>
 <li><code>String</code> -- <code>String.class</code></li>
 <li><code>Nodeset</code> -- <code>XPathNodes.class</code></li>
 <li><code>Node</code> -- <code>Node.class</code></li>
 </ul>

 <p>
 Of the subtypes of Number, only Double, Integer and Long are supported.

 <a name="XPath.Datatypes.Enum"></a>
 <h3>3.3 Enum types</h3>
 Enum types are defined in {@link javax.xml.xpath.XPathEvaluationResult.XPathResultType}
 that provide mappings between the QName and Class types above. The result of
 evaluating an expression using the <code>XPathExpression.evaluteExpression(...)</code>
 or <code>XPath.evaluateExpression(...)</code> methods will be of one of these types.

 <a name="XPath.Context"></a>
 <h3>4. XPath Context</h3>

 <p>XPath location paths may be relative to a particular node in the
 document, known as the <code>context</code>. A context consists of:
 <ul>
     <li>a node (the context node)</li>
     <li>a pair of non-zero positive integers (the context position and the context size)</li>
     <li>a set of variable bindings</li>
     <li>a function library</li>
     <li>the set of namespace declarations in scope for the expression</li>
 </ul>

 <p>
 It is an XML document tree represented as a hierarchy of nodes, a
 {@link org.w3c.dom.Node} for example, in the JDK implementation.

 <a name="XPath.Use"></a>
 <h3>5. Using the XPath API</h3>

 Consider the following XML document:
 <blockquote>
 <pre>
 &lt;widgets&gt;
 &lt;widget&gt;
 &lt;manufacturer/&gt;
 &lt;dimensions/&gt;
 &lt;/widget&gt;
 &lt;/widgets&gt;
 </pre>
 </blockquote>

 <p>
 The <code>&lt;widget&gt;</code> element can be selected with the following process:

 <blockquote>
 <pre>
 // parse the XML as a W3C Document
 DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
 Document document = builder.parse(new File("/widgets.xml"));

 //Get an XPath object and evaluate the expression
 XPath xpath = XPathFactory.newInstance().newXPath();
 String expression = "/widgets/widget";
 Node widgetNode = (Node) xpath.evaluate(expression, document, XPathConstants.NODE);

 //or using the evaluateExpression method
 Node widgetNode = xpath.evaluateExpression(expression, document, Node.class);
 </pre>
 </blockquote>

 <p>With a reference to the <code>&lt;widget&gt;</code> element, a
 relative XPath expression can be written to select the
 <code>&lt;manufacturer&gt;</code> child element:</p>

 <blockquote>
 <pre>
 XPath xpath = XPathFactory.newInstance().newXPath();
 <strong>String expression = "manufacturer";</strong>
 Node manufacturerNode = (Node) xpath.evaluate(expression, <strong>widgetNode</strong>, XPathConstants.NODE);

 //or using the evaluateExpression method
 Node manufacturerNode = xpath.evaluateExpression(expression, <strong>widgetNode</strong>, Node.class);
 </pre>
 </blockquote>

 <p>
 In the above example, the XML file is read into a DOM Document before being passed
 to the XPath API. The following code demonstrates the use of InputSource to
 leave it to the XPath implementation to process it:

 <blockquote>
 <pre>
 XPath xpath = XPathFactory.newInstance().newXPath();
 String expression = "/widgets/widget";
 InputSource inputSource = new InputSource("widgets.xml");
 NodeList nodes = (NodeList) xpath.evaluate(expression, inputSource, XPathConstants.NODESET);

 //or using the evaluateExpression method
 XPathNodes nodes = xpath.evaluate(expression, inputSource, XPathNodes.class);
 </pre>
 </blockquote>

 <p>
 In the above cases, the type of the expected results are known. In case where
 the result type is unknown or any type, the {@link javax.xml.xpath.XPathEvaluationResult}
 may be used to determine the return type. The following code demonstrates the usage:
 <blockquote>
 <pre>
 XPathEvaluationResult&lt;?&gt; result = xpath.evaluateExpression(expression, document);
 switch (result.type()) {
     case NODESET:
         XPathNodes nodes = (XPathNodes)result.value();
         ...
         break;
 }
 </pre>
 </blockquote>

 <p>
 The XPath 1.0 Number data type is defined as a double. However, the XPath
 specification also provides functions that returns Integer type. To facilitate
 such operations, the XPath API allows Integer and Long to be used in
 {@code evaluateExpression} method such as the following code:
 <blockquote>
 <pre>
 int count = xpath.evaluate("count(/widgets/widget)", document, Integer.class);
 </pre>
 </blockquote>

 @since 1.5

 </body>
 </html>
	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
	<html>
	<head>
	<!--
	Copyright (c) 2003, 2015, Oracle and/or its affiliates. All rights reserved.
	DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

	This code is free software; you can redistribute it and/or modify it
	under the terms of the GNU General Public License version 2 only, as
	published by the Free Software Foundation. Oracle designates this
	particular file as subject to the "Classpath" exception as provided
	by Oracle in the LICENSE file that accompanied this code.

	This code is distributed in the hope that it will be useful, but WITHOUT
	ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	version 2 for more details (a copy is included in the LICENSE file that
	accompanied this code).

	You should have received a copy of the GNU General Public License version
	2 along with this work; if not, write to the Free Software Foundation,
	Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

	Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	or visit www.oracle.com if you need additional information or have any
	questions.
	-->
	</head>
	<body bgcolor="white">

	This package provides an <em>object-model neutral</em> API for the
	evaluation of XPath expressions and access to the evaluation
	environment.

	<p>
	The XPath API supports <a href="http://www.w3.org/TR/xpath">
	XML Path Language (XPath) Version 1.0</a>

	<hr />

	<ul>
	<li><a href='#XPath.Overview'>1. XPath Overview</a></li>
	<li><a href='#XPath.Expressions'>2. XPath Expressions</a></li>
	<li><a href='#XPath.Datatypes'>3. XPath Data Types</a>
	<ul>
	<li><a href='#XPath.Datatypes.QName'>3.1 QName Types</a>
	<li><a href='#XPath.Datatypes.Class'>3.2 Class Types</a>
	<li><a href='#XPath.Datatypes.Enum'>3.3 Enum Types</a>
	</ul>
	</li>
	<li><a href='#XPath.Context'>4. XPath Context</a></li>
	<li><a href='#XPath.Use'>5. Using the XPath API</a></li>
	</ul>
	<p>
	<a name="XPath.Overview"></a>
	<h3>1. XPath Overview</h3>

	<p>The XPath language provides a simple, concise syntax for selecting
	nodes from an XML document. XPath also provides rules for converting a
	node in an XML document object model (DOM) tree to a boolean, double,
	or string value. XPath is a W3C-defined language and an official W3C
	recommendation; the W3C hosts the XML Path Language (XPath) Version
	1.0 specification.
	</p>

	<p>XPath started in life in 1999 as a supplement to the XSLT and
	XPointer languages, but has more recently become popular as a
	stand-alone language, as a single XPath expression can be used to
	replace many lines of DOM API code.
	</p>

	<a name="XPath.Expressions"></a>
	<h3>2. XPath Expressions</h3>

	<p>An XPath <em>expression</em> is composed of a <em>location
	path</em> and one or more optional <em>predicates</em>. Expressions
	may also include XPath variables.
	</p>

	<p>The following is an example of a simple XPath expression:</p>

	<blockquote>
	<pre>
	/foo/bar
	</pre>
	</blockquote>

	<p>This example would select the <code><bar></code> element in
	an XML document such as the following:</p>

	<blockquote>
	<pre>
	<foo>
	<bar/>
	</foo>
	</pre>
	</blockquote>

	<p>The expression <code>/foo/bar</code> is an example of a location
	path. While XPath location paths resemble Unix-style file system
	paths, an important distinction is that XPath expressions return
	<em>all</em> nodes that match the expression. Thus, all three
	<code><bar></code> elements in the following document would be
	selected by the <code>/foo/bar</code> expression:</p>

	<blockquote>
	<pre>
	<foo>
	<bar/>
	<bar/>
	<bar/>
	</foo>
	</pre>
	</blockquote>

	<p>A special location path operator, <code>//</code>, selects nodes at
	any depth in an XML document. The following example selects all
	<code><bar></code> elements regardless of their location in a
	document:</p>

	<blockquote>
	<pre>
	//bar
	</pre>
	</blockquote>

	<p>A wildcard operator, *, causes all element nodes to be selected.
	The following example selects all children elements of a
	<code><foo></code> element:

	<blockquote>
	<pre>
	/foo/*
	</pre>
	</blockquote>

	<p>In addition to element nodes, XPath location paths may also address
	attribute nodes, text nodes, comment nodes, and processing instruction
	nodes. The following table gives examples of location paths for each
	of these node types:</p>

	<table border="1">
	<tr>
	<td>Location Path</td>
	<td>Description</td>
	</tr>
	<tr>
	<td>
	<code>/foo/bar/<strong>@id</strong></code>
	</td>
	<td>Selects the attribute <code>id</code> of the <code><bar></code> element
	</td>
	</tr>
	<tr>
	<td><code>/foo/bar/<strong>text()</strong></code>
	</td>
	<td>Selects the text nodes of the <code><bar></code> element. No
	distinction is made between escaped and non-escaped character data.
	</td>
	</tr>
	<tr>
	<td><code>/foo/bar/<strong>comment()</strong></code>
	</td>
	<td>Selects all comment nodes contained in the <code><bar></code> element.
	</td>
	</tr>
	<tr>
	<td><code>/foo/bar/<strong>processing-instruction()</strong></code>
	</td>
	<td>Selects all processing-instruction nodes contained in the
	<code><bar></code> element.
	</td>
	</tr>
	</table>

	<p>Predicates allow for refining the nodes selected by an XPath
	location path. Predicates are of the form
	<code>[<em>expression</em>]</code>. The following example selects all
	<code><foo></code> elements that contain an <code>include</code>
	attribute with the value of <code>true</code>:</p>

	<blockquote>
	<pre>
	//foo[@include='true']
	</pre>
	</blockquote>

	<p>Predicates may be appended to each other to further refine an
	expression, such as:</p>

	<blockquote>
	<pre>
	//foo[@include='true'][@mode='bar']
	</pre>
	</blockquote>

	<a name="XPath.Datatypes"></a>
	<h3>3. XPath Data Types</h3>

	<p>While XPath expressions select nodes in the XML document, the XPath
	API allows the selected nodes to be coalesced into one of the
	following data types:</p>

	<ul>
	<li><code>Boolean</code></li>
	<li><code>Number</code></li>
	<li><code>String</code></li>
	</ul>

	<a name="XPath.Datatypes.QName"></a>
	<h3>3.1 QName types</h3>
	The XPath API defines the following {@link javax.xml.namespace.QName} types to
	represent return types of an XPath evaluation:
	<ul>
	<li>{@link javax.xml.xpath.XPathConstants#NODESET}</li>
	<li>{@link javax.xml.xpath.XPathConstants#NODE}</li>
	<li>{@link javax.xml.xpath.XPathConstants#STRING}</li>
	<li>{@link javax.xml.xpath.XPathConstants#BOOLEAN}</li>
	<li>{@link javax.xml.xpath.XPathConstants#NUMBER}</li>
	</ul>

	<p>The return type is specified by a {@link javax.xml.namespace.QName} parameter
	in method call used to evaluate the expression, which is either a call to
	<code>XPathExpression.evalute(...)</code> or <code>XPath.evaluate(...)</code>
	methods.

	<p>When a <code>Boolean</code> return type is requested,
	<code>Boolean.TRUE</code> is returned if one or more nodes were
	selected; otherwise, <code>Boolean.FALSE</code> is returned.

	<p>The <code>String</code> return type is a convenience for retrieving
	the character data from a text node, attribute node, comment node, or
	processing-instruction node. When used on an element node, the value
	of the child text nodes is returned.

	<p>The <code>Number</code> return type attempts to coalesce the text
	of a node to a <code>double</code> data type.

	<a name="XPath.Datatypes.Class"></a>
	<h3>3.2 Class types</h3>
	In addition to the QName types, the XPath API supports the use of Class types
	through the <code>XPathExpression.evaluteExpression(...)</code> or
	<code>XPath.evaluateExpression(...)</code> methods.

	The XPath data types are mapped to Class types as follows:
	<ul>
	<li><code>Boolean</code> -- <code>Boolean.class</code></li>
	<li><code>Number</code> -- <code>Number.class</code></li>
	<li><code>String</code> -- <code>String.class</code></li>
	<li><code>Nodeset</code> -- <code>XPathNodes.class</code></li>
	<li><code>Node</code> -- <code>Node.class</code></li>
	</ul>

	<p>
	Of the subtypes of Number, only Double, Integer and Long are supported.

	<a name="XPath.Datatypes.Enum"></a>
	<h3>3.3 Enum types</h3>
	Enum types are defined in {@link javax.xml.xpath.XPathEvaluationResult.XPathResultType}
	that provide mappings between the QName and Class types above. The result of
	evaluating an expression using the <code>XPathExpression.evaluteExpression(...)</code>
	or <code>XPath.evaluateExpression(...)</code> methods will be of one of these types.

	<a name="XPath.Context"></a>
	<h3>4. XPath Context</h3>

	<p>XPath location paths may be relative to a particular node in the
	document, known as the <code>context</code>. A context consists of:
	<ul>
	<li>a node (the context node)</li>
	<li>a pair of non-zero positive integers (the context position and the context size)</li>
	<li>a set of variable bindings</li>
	<li>a function library</li>
	<li>the set of namespace declarations in scope for the expression</li>
	</ul>

	<p>
	It is an XML document tree represented as a hierarchy of nodes, a
	{@link org.w3c.dom.Node} for example, in the JDK implementation.

	<a name="XPath.Use"></a>
	<h3>5. Using the XPath API</h3>

	Consider the following XML document:
	<blockquote>
	<pre>
	<widgets>
	<widget>
	<manufacturer/>
	<dimensions/>
	</widget>
	</widgets>
	</pre>
	</blockquote>

	<p>
	The <code><widget></code> element can be selected with the following process:

	<blockquote>
	<pre>
	// parse the XML as a W3C Document
	DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
	Document document = builder.parse(new File("/widgets.xml"));

	//Get an XPath object and evaluate the expression
	XPath xpath = XPathFactory.newInstance().newXPath();
	String expression = "/widgets/widget";
	Node widgetNode = (Node) xpath.evaluate(expression, document, XPathConstants.NODE);

	//or using the evaluateExpression method
	Node widgetNode = xpath.evaluateExpression(expression, document, Node.class);
	</pre>
	</blockquote>

	<p>With a reference to the <code><widget></code> element, a
	relative XPath expression can be written to select the
	<code><manufacturer></code> child element:</p>

	<blockquote>
	<pre>
	XPath xpath = XPathFactory.newInstance().newXPath();
	<strong>String expression = "manufacturer";</strong>
	Node manufacturerNode = (Node) xpath.evaluate(expression, <strong>widgetNode</strong>, XPathConstants.NODE);

	//or using the evaluateExpression method
	Node manufacturerNode = xpath.evaluateExpression(expression, <strong>widgetNode</strong>, Node.class);
	</pre>
	</blockquote>

	<p>
	In the above example, the XML file is read into a DOM Document before being passed
	to the XPath API. The following code demonstrates the use of InputSource to
	leave it to the XPath implementation to process it:

	<blockquote>
	<pre>
	XPath xpath = XPathFactory.newInstance().newXPath();
	String expression = "/widgets/widget";
	InputSource inputSource = new InputSource("widgets.xml");
	NodeList nodes = (NodeList) xpath.evaluate(expression, inputSource, XPathConstants.NODESET);

	//or using the evaluateExpression method
	XPathNodes nodes = xpath.evaluate(expression, inputSource, XPathNodes.class);
	</pre>
	</blockquote>

	<p>
	In the above cases, the type of the expected results are known. In case where
	the result type is unknown or any type, the {@link javax.xml.xpath.XPathEvaluationResult}
	may be used to determine the return type. The following code demonstrates the usage:
	<blockquote>
	<pre>
	XPathEvaluationResult<?> result = xpath.evaluateExpression(expression, document);
	switch (result.type()) {
	case NODESET:
	XPathNodes nodes = (XPathNodes)result.value();
	...
	break;
	}
	</pre>
	</blockquote>

	<p>
	The XPath 1.0 Number data type is defined as a double. However, the XPath
	specification also provides functions that returns Integer type. To facilitate
	such operations, the XPath API allows Integer and Long to be used in
	{@code evaluateExpression} method such as the following code:
	<blockquote>
	<pre>
	int count = xpath.evaluate("count(/widgets/widget)", document, Integer.class);
	</pre>
	</blockquote>

	@since 1.5

	</body>
	</html>