src/java.xml/share/classes/javax/xml/xpath/package.html
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-<html xmlns="http://www.w3.org/1999/xhtml">
-<head>
-<title>javax.xml.xpath</title>
-<meta name="@author" content="mailto:Ben@galbraiths.org" />
-<meta name="@author" content="mailto:Norman.Walsh@Sun.com" />
-<meta name="@author" content="mailto:Jeff.Suttor@Sun.com" />
-<meta name="@see" content="http://www.w3.org/TR/xpath" />
-<meta name="@since" content="1.5" />
</head>
+<body bgcolor="white">
-<body>
-
-<p>This package provides an <em>object-model neutral</em> API for the
+This package provides an <em>object-model neutral</em> API for the
evaluation of XPath expressions and access to the evaluation
environment.
-</p>
-<p>The following XML standards apply:</p>
+<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="http://www.w3.org/TR/xpath">XML Path Language (XPath) Version 1.0</a></li>
+ <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>
-<hr />
-
-<h2>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
@@ -65,63 +67,74 @@
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>
-<h3>XPath Expressions</h3>
+<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/>
+ <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/>
+ <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:</p>
+<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>
@@ -164,118 +177,203 @@
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>
-<h3>Using the XPath API</h3>
+<a name="XPath.Datatypes"></a>
+<h3>3. XPath Data Types</h3>
-<p>
-The following example demonstrates using the XPath API to select one
-or more nodes from an XML document:</p>
-
-<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);
-</pre>
-
-<h3>XPath Expressions and 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 other data types:</p>
+following data types:</p>
<ul>
<li><code>Boolean</code></li>
<li><code>Number</code></li>
<li><code>String</code></li>
</ul>
-<p>The desired 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 to one of the
-<code>XPath.evaluate(...)</code> convenience methods. The allowed
-QName values are specified as constants in the {@link
-javax.xml.xpath.XPathConstants} class; they are:</p>
-
+<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>
+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>
<p>The <code>Number</code> return type attempts to coalesce the text
of a node to a <code>double</code> data type.
-</p>
-<h3>XPath Context</h3>
+<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>. Consider the following
-XML document:</p>
+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:
+<p>
+<blockquote>
<pre>
<widgets>
<widget>
<manufacturer/>
<dimensions/>
</widget>
</widgets>
</pre>
+</blockquote>
-<p>The <code><widget></code> element can be selected with the
-following XPath API code:</p>
+<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 now written to select the
+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>
-<ul>
-<li>Author <a href="mailto:Ben@galbraiths.org">Ben Galbraith</a></li>
-<li>Author <a href="mailto:Norman.Walsh@Sun.com">Norman Walsh</a></li>
-<li>Author <a href="mailto:Jeff.Suttor@Sun.com">Jeff Suttor</a></li>
-<li>See <a href="http://www.w3.org/TR/xpath">XML Path Language (XPath) Version 1.0</a></li>
-<li>Since 1.5</li>
-</ul>
+<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:
+<p>
+<blockquote>
+<pre>
+int count = xpath.evaluate("count(/widgets/widget)", document, Integer.class);
+</pre>
+</blockquote>
+
+@since 1.5
+
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