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25
26 /**
27 *
28 * Provides an <em>object-model neutral</em> API for the
29 * evaluation of XPath expressions and access to the evaluation
30 * environment.
31 *
32 * <p>
33 * The XPath API supports <a href="http://www.w3.org/TR/xpath">
34 * XML Path Language (XPath) Version 1.0</a>
35 *
36 * <hr>
37 *
38 * <ul>
39 * <li><a href='#XPath.Overview'>1. XPath Overview</a></li>
40 * <li><a href='#XPath.Expressions'>2. XPath Expressions</a></li>
41 * <li><a href='#XPath.Datatypes'>3. XPath Data Types</a>
42 * <ul>
43 * <li><a href='#XPath.Datatypes.QName'>3.1 QName Types</a>
44 * <li><a href='#XPath.Datatypes.Class'>3.2 Class Types</a>
45 * <li><a href='#XPath.Datatypes.Enum'>3.3 Enum Types</a>
46 * </ul>
47 * </li>
48 * <li><a href='#XPath.Context'>4. XPath Context</a></li>
49 * <li><a href='#XPath.Use'>5. Using the XPath API</a></li>
50 * </ul>
51 * <p>
52 * <a id="XPath.Overview"></a>
53 * <h3>1. XPath Overview</h3>
54 *
55 * <p>
56 * The XPath language provides a simple, concise syntax for selecting
57 * nodes from an XML document. XPath also provides rules for converting a
58 * node in an XML document object model (DOM) tree to a boolean, double,
59 * or string value. XPath is a W3C-defined language and an official W3C
60 * recommendation; the W3C hosts the XML Path Language (XPath) Version
61 * 1.0 specification.
62 *
63 *
64 * <p>
65 * XPath started in life in 1999 as a supplement to the XSLT and
66 * XPointer languages, but has more recently become popular as a
67 * stand-alone language, as a single XPath expression can be used to
68 * replace many lines of DOM API code.
69 *
70 *
71 * <a id="XPath.Expressions"></a>
72 * <h3>2. XPath Expressions</h3>
73 *
74 * <p>
75 * An XPath <em>expression</em> is composed of a <em>location
76 * path</em> and one or more optional <em>predicates</em>. Expressions
77 * may also include XPath variables.
78 *
79 *
80 * <p>
81 * The following is an example of a simple XPath expression:
82 *
83 * <blockquote>
84 * <pre>
85 * /foo/bar
86 * </pre>
87 * </blockquote>
88 *
89 * <p>
90 * This example would select the <code><bar></code> element in
91 * an XML document such as the following:
92 *
93 * <blockquote>
94 * <pre>
95 * <foo>
96 * <bar/>
97 * </foo>
98 * </pre>
99 * </blockquote>
100 *
101 * <p>The expression <code>/foo/bar</code> is an example of a location
102 * path. While XPath location paths resemble Unix-style file system
103 * paths, an important distinction is that XPath expressions return
104 * <em>all</em> nodes that match the expression. Thus, all three
105 * <code><bar></code> elements in the following document would be
106 * selected by the <code>/foo/bar</code> expression:
107 *
108 * <blockquote>
109 * <pre>
110 * <foo>
111 * <bar/>
112 * <bar/>
113 * <bar/>
114 * </foo>
115 * </pre>
116 * </blockquote>
117 *
118 * <p>
119 * A special location path operator, <code>//</code>, selects nodes at
120 * any depth in an XML document. The following example selects all
121 * <code><bar></code> elements regardless of their location in a
122 * document:
123 *
124 * <blockquote>
125 * <pre>
126 * //bar
127 * </pre>
128 * </blockquote>
129 *
130 * <p>
131 * A wildcard operator, *, causes all element nodes to be selected.
132 * The following example selects all children elements of a
133 * <code><foo></code> element:
134 *
135 * <blockquote>
136 * <pre>
137 * /foo/*
138 * </pre>
139 * </blockquote>
140 *
141 * <p>
142 * In addition to element nodes, XPath location paths may also address
143 * attribute nodes, text nodes, comment nodes, and processing instruction
144 * nodes. The following table gives examples of location paths for each
145 * of these node types:
146 *
147 * <table class="striped">
148 * <caption>Examples of Location Path</caption>
149 * <thead>
150 * <tr>
151 * <th scope="col">Location Path</th>
152 * <th scope="col">Description</th>
153 * </tr>
154 * </thead>
155 * <tbody>
156 * <tr>
157 * <th scope="row">
158 * <code>/foo/bar/<strong>@id</strong></code>
159 * </th>
160 * <td>
161 * Selects the attribute <code>id</code> of the <code><bar></code> element
162 * </td>
163 * </tr>
164 * <tr>
165 * <th scope="row"><code>/foo/bar/<strong>text()</strong></code>
166 * </th>
167 * <td>
168 * Selects the text nodes of the <code><bar></code> element. No
169 * distinction is made between escaped and non-escaped character data.
170 * </td>
171 * </tr>
172 * <tr>
173 * <th scope="row"><code>/foo/bar/<strong>comment()</strong></code>
174 * </th>
175 * <td>
176 * Selects all comment nodes contained in the <code><bar></code> element.
177 * </td>
178 * </tr>
179 * <tr>
180 * <th scope="row"><code>/foo/bar/<strong>processing-instruction()</strong></code>
181 * </th>
182 * <td>
183 * Selects all processing-instruction nodes contained in the
184 * <code><bar></code> element.
185 * </td>
186 * </tr>
187 * </tbody>
188 * </table>
189 *
190 * <p>
191 * Predicates allow for refining the nodes selected by an XPath
192 * location path. Predicates are of the form
193 * <code>[<em>expression</em>]</code>. The following example selects all
194 * <code><foo></code> elements that contain an <code>include</code>
195 * attribute with the value of <code>true</code>:
196 *
197 * <blockquote>
198 * <pre>
199 * //foo[@include='true']
200 * </pre>
201 * </blockquote>
202 *
203 * <p>
204 * Predicates may be appended to each other to further refine an
205 * expression, such as:
206 *
207 * <blockquote>
208 * <pre>
209 * //foo[@include='true'][@mode='bar']
210 * </pre>
211 * </blockquote>
212 *
213 * <a id="XPath.Datatypes"></a>
214 * <h3>3. XPath Data Types</h3>
215 *
216 * <p>
217 * While XPath expressions select nodes in the XML document, the XPath
218 * API allows the selected nodes to be coalesced into one of the
219 * following data types:
220 *
221 * <ul>
222 * <li><code>Boolean</code></li>
223 * <li><code>Number</code></li>
224 * <li><code>String</code></li>
225 * </ul>
226 *
227 * <a id="XPath.Datatypes.QName"></a>
228 * <h3>3.1 QName types</h3>
229 * The XPath API defines the following {@link javax.xml.namespace.QName} types to
230 * represent return types of an XPath evaluation:
231 * <ul>
232 * <li>{@link javax.xml.xpath.XPathConstants#NODESET}</li>
233 * <li>{@link javax.xml.xpath.XPathConstants#NODE}</li>
234 * <li>{@link javax.xml.xpath.XPathConstants#STRING}</li>
235 * <li>{@link javax.xml.xpath.XPathConstants#BOOLEAN}</li>
236 * <li>{@link javax.xml.xpath.XPathConstants#NUMBER}</li>
237 * </ul>
238 *
239 * <p>
240 * The return type is specified by a {@link javax.xml.namespace.QName} parameter
241 * in method call used to evaluate the expression, which is either a call to
242 * <code>XPathExpression.evalute(...)</code> or <code>XPath.evaluate(...)</code>
243 * methods.
244 *
245 * <p>
246 * When a <code>Boolean</code> return type is requested,
247 * <code>Boolean.TRUE</code> is returned if one or more nodes were
248 * selected; otherwise, <code>Boolean.FALSE</code> is returned.
249 *
250 * <p>
251 * The <code>String</code> return type is a convenience for retrieving
252 * the character data from a text node, attribute node, comment node, or
253 * processing-instruction node. When used on an element node, the value
254 * of the child text nodes is returned.
255 *
256 * <p>
257 * The <code>Number</code> return type attempts to coalesce the text
258 * of a node to a <code>double</code> data type.
259 *
260 * <a id="XPath.Datatypes.Class"></a>
261 * <h3>3.2 Class types</h3>
262 * In addition to the QName types, the XPath API supports the use of Class types
263 * through the <code>XPathExpression.evaluteExpression(...)</code> or
264 * <code>XPath.evaluateExpression(...)</code> methods.
265 *
266 * The XPath data types are mapped to Class types as follows:
267 * <ul>
268 * <li><code>Boolean</code> -- <code>Boolean.class</code></li>
269 * <li><code>Number</code> -- <code>Number.class</code></li>
270 * <li><code>String</code> -- <code>String.class</code></li>
271 * <li><code>Nodeset</code> -- <code>XPathNodes.class</code></li>
272 * <li><code>Node</code> -- <code>Node.class</code></li>
273 * </ul>
274 *
275 * <p>
276 * Of the subtypes of Number, only Double, Integer and Long are supported.
277 *
278 * <a id="XPath.Datatypes.Enum"></a>
279 * <h3>3.3 Enum types</h3>
280 * Enum types are defined in {@link javax.xml.xpath.XPathEvaluationResult.XPathResultType}
281 * that provide mappings between the QName and Class types above. The result of
282 * evaluating an expression using the <code>XPathExpression.evaluteExpression(...)</code>
283 * or <code>XPath.evaluateExpression(...)</code> methods will be of one of these types.
284 *
285 * <a id="XPath.Context"></a>
286 * <h3>4. XPath Context</h3>
287 *
288 * <p>
289 * XPath location paths may be relative to a particular node in the
290 * document, known as the <code>context</code>. A context consists of:
291 * <ul>
292 * <li>a node (the context node)</li>
293 * <li>a pair of non-zero positive integers (the context position and the context size)</li>
294 * <li>a set of variable bindings</li>
295 * <li>a function library</li>
296 * <li>the set of namespace declarations in scope for the expression</li>
297 * </ul>
298 *
299 * <p>
300 * It is an XML document tree represented as a hierarchy of nodes, a
301 * {@link org.w3c.dom.Node} for example, in the JDK implementation.
302 *
303 * <a id="XPath.Use"></a>
304 * <h3>5. Using the XPath API</h3>
305 *
306 * Consider the following XML document:
307 * <blockquote>
308 * <pre>
309 * <widgets>
310 * <widget>
311 * <manufacturer/>
312 * <dimensions/>
313 * </widget>
314 * </widgets>
315 * </pre>
316 * </blockquote>
317 *
318 * <p>
319 * The <code><widget></code> element can be selected with the following process:
320 *
321 * <blockquote>
322 * <pre>
323 * // parse the XML as a W3C Document
324 * DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
325 * Document document = builder.parse(new File("/widgets.xml"));
326 *
327 * //Get an XPath object and evaluate the expression
328 * XPath xpath = XPathFactory.newInstance().newXPath();
329 * String expression = "/widgets/widget";
330 * Node widgetNode = (Node) xpath.evaluate(expression, document, XPathConstants.NODE);
331 *
332 * //or using the evaluateExpression method
333 * Node widgetNode = xpath.evaluateExpression(expression, document, Node.class);
334 * </pre>
335 * </blockquote>
336 *
337 * <p>
338 * With a reference to the <code><widget></code> element, a
339 * relative XPath expression can be written to select the
340 * <code><manufacturer></code> child element:
341 *
342 * <blockquote>
343 * <pre>
344 * XPath xpath = XPathFactory.newInstance().newXPath();
345 * String expression = <b>"manufacturer";</b>
346 * Node manufacturerNode = (Node) xpath.evaluate(expression, <b>widgetNode</b>, XPathConstants.NODE);
347 *
348 * //or using the evaluateExpression method
349 * Node manufacturerNode = xpath.evaluateExpression(expression, <b>widgetNode</b>, Node.class);
350 * </pre>
351 * </blockquote>
352 *
353 * <p>
354 * In the above example, the XML file is read into a DOM Document before being passed
355 * to the XPath API. The following code demonstrates the use of InputSource to
356 * leave it to the XPath implementation to process it:
357 *
358 * <blockquote>
359 * <pre>
360 * XPath xpath = XPathFactory.newInstance().newXPath();
361 * String expression = "/widgets/widget";
362 * InputSource inputSource = new InputSource("widgets.xml");
363 * NodeList nodes = (NodeList) xpath.evaluate(expression, inputSource, XPathConstants.NODESET);
364 *
365 * //or using the evaluateExpression method
366 * XPathNodes nodes = xpath.evaluate(expression, inputSource, XPathNodes.class);
367 * </pre>
368 * </blockquote>
369 *
370 * <p>
371 * In the above cases, the type of the expected results are known. In case where
372 * the result type is unknown or any type, the {@link javax.xml.xpath.XPathEvaluationResult}
373 * may be used to determine the return type. The following code demonstrates the usage:
374 * <blockquote>
375 * <pre>
376 * XPathEvaluationResult<?> result = xpath.evaluateExpression(expression, document);
377 * switch (result.type()) {
378 * case NODESET:
379 * XPathNodes nodes = (XPathNodes)result.value();
380 * ...
381 * break;
382 * }
383 * </pre>
384 * </blockquote>
385 *
386 * <p>
387 * The XPath 1.0 Number data type is defined as a double. However, the XPath
388 * specification also provides functions that returns Integer type. To facilitate
389 * such operations, the XPath API allows Integer and Long to be used in
390 * {@code evaluateExpression} method such as the following code:
391 * <blockquote>
392 * <pre>
393 * int count = xpath.evaluate("count(/widgets/widget)", document, Integer.class);
394 * </pre>
395 * </blockquote>
396 *
397 * @since 1.5
398 *
399 */
400
401 package javax.xml.xpath;