java/13 : java.xml/javax/xml/xpath/package-info.java

javax.xml.xpath
https://openjdk.java.net/
GPLv2 + Classpath Exception
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Provides an object-model neutral API for the
evaluation of XPath expressions and access to the evaluation
environment.

The XPath API supports 
    XML Path Language (XPath) Version 1.0


    1. XPath Overview
    2. XPath Expressions
    3. XPath Data Types
        
            3.1 QName Types
            
3.2 Class Types
            
3.3 Enum Types
        
    
    4. XPath Context
    5. Using the XPath API



1. XPath Overview

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.

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.

2. XPath Expressions

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

The following is an example of a simple XPath expression:

    /foo/bar



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

    <foo>
        <bar/>
    </foo>


The expression /foo/bar 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
all nodes that match the expression. Thus, all three
<bar> elements in the following document would be
selected by the /foo/bar expression:

    <foo>
        <bar/>
        <bar/>
        <bar/>
    </foo>



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

    //bar



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

    /foo/*



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:

    Examples of Location Path
    
        
            Location Path
            Description
        
    
    
        
            
                /foo/bar/@id
            
            
                Selects the attribute id of the <bar> element
            
        
        
            /foo/bar/text()
            
            
                Selects the text nodes of the <bar> element. No
                distinction is made between escaped and non-escaped character data.
            
        
        
            /foo/bar/comment()
            
            
                Selects all comment nodes contained in the <bar> element.
            
        
        
            /foo/bar/processing-instruction()
            
            
                Selects all processing-instruction nodes contained in the
                <bar> element.
            
        
    


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

    //foo[@include='true']



Predicates may be appended to each other to further refine an
expression, such as:

    //foo[@include='true'][@mode='bar']



3. XPath Data Types

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:

    Boolean
    Number
    String


3.1 QName types
 The XPath API defines the following QName types to represent return types of an XPath evaluation: 
    XPathConstants.NODESET
    XPathConstants.NODE
    XPathConstants.STRING
    XPathConstants.BOOLEAN
    XPathConstants.NUMBER

 The return type is specified by a QName parameter in method call used to evaluate the expression, which is either a call to XPathExpression.evalute(...) or XPath.evaluate(...)
methods.

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

The String 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.

The Number return type attempts to coalesce the text
of a node to a double data type.

3.2 Class types
In addition to the QName types, the XPath API supports the use of Class types
through the XPathExpression.evaluteExpression(...) or
XPath.evaluateExpression(...) methods.
The XPath data types are mapped to Class types as follows:

    Boolean -- Boolean.class
    Number -- Number.class
    String -- String.class
    Nodeset -- XPathNodes.class
    Node -- Node.class


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

3.3 Enum types
 Enum types are defined in XPathResultType that provide mappings between the QName and Class types above. The result of evaluating an expression using the XPathExpression.evaluteExpression(...)
or XPath.evaluateExpression(...) methods will be of one of these types.

4. XPath Context

XPath location paths may be relative to a particular node in the
document, known as the context. A context consists of:

    a node (the context node)
    a pair of non-zero positive integers (the context position and the context size)
    a set of variable bindings
    a function library
    the set of namespace declarations in scope for the expression

 It is an XML document tree represented as a hierarchy of nodes, a Node for example, in the JDK implementation. 
5. Using the XPath API
Consider the following XML document:

<widgets>
<widget>
<manufacturer/>
<dimensions/>
</widget>
</widgets>



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

    // 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);



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

    XPath xpath = XPathFactory.newInstance().newXPath();
    String expression = "manufacturer";
    Node manufacturerNode = (Node) xpath.evaluate(expression, widgetNode, XPathConstants.NODE);
    //or using the evaluateExpression method
    Node manufacturerNode = xpath.evaluateExpression(expression, widgetNode, Node.class);



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:

    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);


 In the above cases, the type of the expected results are known. In case where the result type is unknown or any type, the XPathEvaluationResult may be used to determine the return type. The following code demonstrates the usage: 

    XPathEvaluationResult<?> result = xpath.evaluateExpression(expression, document);
    switch (result.type()) {
        case NODESET:
            XPathNodes nodes = (XPathNodes)result.value();
            ...
            break;
    }


 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 evaluateExpression method such as the following code: 

    int count = xpath.evaluate("count(/widgets/widget)", document, Integer.class);


Since: 1.5/**
 *
 * 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 id="XPath.Overview"></a>
 * <h2>1. XPath Overview</h2>
 *
 * <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>
 * 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.
 *
 *
 * <a id="XPath.Expressions"></a>
 * <h2>2. XPath Expressions</h2>
 *
 * <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>
 * The following is an example of a simple XPath expression:
 *
 * <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:
 *
 * <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:
 *
 * <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:
 *
 * <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:
 *
 * <table class="striped">
 *     <caption>Examples of Location Path</caption>
 *     <thead>
 *         <tr>
 *             <th scope="col">Location Path</th>
 *             <th scope="col">Description</th>
 *         </tr>
 *     </thead>
 *     <tbody>
 *         <tr>
 *             <th scope="row">
 *                 <code>/foo/bar/<strong>@id</strong></code>
 *             </th>
 *             <td>
 *                 Selects the attribute <code>id</code> of the <code>&lt;bar&gt;</code> element
 *             </td>
 *         </tr>
 *         <tr>
 *             <th scope="row"><code>/foo/bar/<strong>text()</strong></code>
 *             </th>
 *             <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>
 *             <th scope="row"><code>/foo/bar/<strong>comment()</strong></code>
 *             </th>
 *             <td>
 *                 Selects all comment nodes contained in the <code>&lt;bar&gt;</code> element.
 *             </td>
 *         </tr>
 *         <tr>
 *             <th scope="row"><code>/foo/bar/<strong>processing-instruction()</strong></code>
 *             </th>
 *             <td>
 *                 Selects all processing-instruction nodes contained in the
 *                 <code>&lt;bar&gt;</code> element.
 *             </td>
 *         </tr>
 *     </tbody>
 * </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>:
 *
 * <blockquote>
 * <pre>
 *     //foo[@include='true']
 * </pre>
 * </blockquote>
 *
 * <p>
 * Predicates may be appended to each other to further refine an
 * expression, such as:
 *
 * <blockquote>
 * <pre>
 *     //foo[@include='true'][@mode='bar']
 * </pre>
 * </blockquote>
 *
 * <a id="XPath.Datatypes"></a>
 * <h2>3. XPath Data Types</h2>
 *
 * <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:
 *
 * <ul>
 *     <li><code>Boolean</code></li>
 *     <li><code>Number</code></li>
 *     <li><code>String</code></li>
 * </ul>
 *
 * <a id="XPath.Datatypes.QName"></a>
 * <h2>3.1 QName types</h2>
 * 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 id="XPath.Datatypes.Class"></a>
 * <h2>3.2 Class types</h2>
 * 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 id="XPath.Datatypes.Enum"></a>
 * <h2>3.3 Enum types</h2>
 * 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 id="XPath.Context"></a>
 * <h2>4. XPath Context</h2>
 *
 * <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 id="XPath.Use"></a>
 * <h2>5. Using the XPath API</h2>
 *
 * 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:
 *
 * <blockquote>
 * <pre>
 *     XPath xpath = XPathFactory.newInstance().newXPath();
 *     String expression = <b>"manufacturer";</b>
 *     Node manufacturerNode = (Node) xpath.evaluate(expression, <b>widgetNode</b>, XPathConstants.NODE);
 *
 *     //or using the evaluateExpression method
 *     Node manufacturerNode = xpath.evaluateExpression(expression, <b>widgetNode</b>, 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
 *
 */

package javax.xml.xpath;
Location Path	Description
`/foo/bar/@id`	Selects the attribute `id` of the `<bar>` element
`/foo/bar/text()`	Selects the text nodes of the `<bar>` element. No distinction is made between escaped and non-escaped character data.
`/foo/bar/comment()`	Selects all comment nodes contained in the `<bar>` element.
`/foo/bar/processing-instruction()`	Selects all processing-instruction nodes contained in the `<bar>` element.
/

java/ 13/ java.xml/javax/xml/xpath/package-info.java

1. XPath Overview

2. XPath Expressions

3. XPath Data Types

3.1 QName types

3.2 Class types

3.3 Enum types

4. XPath Context

5. Using the XPath API
