xpath_getchildelem.html
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<TITLE>Selecting from a Set of Child Elements in a DOM Document Using XPath
(Java Developers Almanac Example)
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<B><A HREF="../org.w3c.dom/pkg.html#XPath">XPath</A></B><font color="#666666" SIZE="-2">
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<h3>
e549.
Selecting from a Set of Child Elements in a DOM Document Using XPath</h3>
XPath is an expression language for selecting nodes in an XML file.
See <a href="../org.w3c.dom/xpath_GetAbsElem.html" class="eglink"><font size="-1"><b>e548</b> Finding Elements by Absolute Location in a DOM Document Using XPath</font></a> for common XPath
expression for selecting elements. This example adds to those
examples by demonstrating the ability to apply a selection filter to a
set of child elements. For example, if an element <code>A</code> contained
several <code>B</code> elements, you could include only the first <code>B</code>
element or all but the first <code>B</code> element.
<P> Filtering in XPath is specified with a <font color="#0066ff"><i>predicate</i></font> after
the element name. A predicate has the form
<code>[</code><font color="#0066ff"><i>expression</i></font><code>]</code>. For example,
<pre>
/book/chapter[2]/section[3]
</pre>
selects the 3rd <code>section</code> element from the 2nd <code>chapter</code> element
under the root element <code>book</code>.
<P> This example demonstrates some common filters; for more
information on XPath, see the specification at
<a href="http://www.w3c.org/TR/xpath"><font size="-1">http://www.w3c.org/TR/xpath</font></a>. In the example, the result of an
XPath expression is shown next to the expression; the numbers are ids
of elements in the sample file shown at the end of the example.
<pre>
// Get the first element under the root
String xpath = "/*/*[1]"; // 2
// Get the second elem1 element under the root
xpath = "/root/elem1[2]"; // 8
// Get all <font color="#0066ff"><i>first-born</i></font> e elements in the document; that is, for all
// e elements with e element siblings, include only the first sibling
xpath = "//e[1]"; // 4 6 10 12
</pre>
Note that <code>//e[1]</code> does not return the first e element in the
document because the <code>[1]</code> predicate applies to <code>e</code>, which
represents the <font color="#0066ff"><i>set</i></font> of <code>e</code> elements under one element and not
to <code>//e</code>, which represents the set of <code>e</code> elements in the
document. The following expression retrieves the first <code>e</code> element
in the document:
<pre>
// Get the first e element in the document
xpath = "(//e)[1]"; // 4
// For all e elements with e element siblings, include only
// the first 3 siblings
xpath = "//e[position() <= 3]"; // 4 6 10 11 12
// Get all <font color="#0066ff"><i>last-born</i></font> e elements in the document; that is, for all
// e elements with e element siblings, include only the last sibling
xpath = "//e[last()]"; // 4 6 11 12
// Get the last e element in the document
xpath = "(//e)[last()]"; // 12
</pre>
To execute an XPath expression, see
<a href="../org.w3c.dom/xpath_GetAbsElem.html" class="eglink"><font size="-1"><b>e548</b> Finding Elements by Absolute Location in a DOM Document Using XPath</font></a>. Here is the sample XML file
used in the example:
<pre>
<?xml version="1.0" encoding="UTF-8"?>
<root id="1">
<elem1 id="2">
<elem2 id="3">
<e id="4"/>
<elem3 id="5">
<e id="6"/>
</elem3>
<elem3 id="7"/>
</elem2>
</elem1>
<elem1 id="8">
<elem2 id="9"/>
<e id="10"/>
<e id="11"/>
</elem1>
<e id="12"/>
</root>
</pre>
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Related Examples
</font></td>
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e548. <a class="eglink" href="xpath_GetAbsElem.html?l=rel">
Finding Elements by Absolute Location in a DOM Document Using XPath
</a>
<br>
e550. <a class="eglink" href="xpath_GetElemByText.html?l=rel">
Finding Elements by Content in a DOM Document Using XPath
</a>
<br>
e551. <a class="eglink" href="xpath_GetElemById.html?l=rel">
Finding Elements by Id in a DOM Document Using XPath
</a>
<br>
e552. <a class="eglink" href="xpath_GetElemByAttr.html?l=rel">
Finding Elements by Attributes in a DOM Document Using XPath
</a>
<br>
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<br>
See also:
<a class="eglink" href="/egs/org.w3c.dom/pkg.html?l=rel#Adding%20and%20Removing%20Nodes">
Adding and Removing Nodes
</a>
<a class="eglink" href="/egs/org.w3c.dom/pkg.html?l=rel#Element%20Attributes">
Element Attributes
</a>
<a class="eglink" href="/egs/org.w3c.dom/pkg.html?l=rel#Elements">
Elements
</a>
<a class="eglink" href="/egs/org.w3c.dom/pkg.html?l=rel#Getting%20Nodes">
Getting Nodes
</a>
<a class="eglink" href="/egs/org.w3c.dom/pkg.html?l=rel#Text%20Nodes">
Text Nodes
</a>
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