xpath_getabselem.html
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<TITLE>Finding Elements by Absolute Location in a DOM Document Using XPath
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<h3>
e548.
Finding Elements by Absolute Location in a DOM Document Using XPath</h3>
XPath is an expression language for selecting nodes in an XML file.
For example, the XPath expression <code>/a/b</code> selects all <code>b</code>
elements under the root element <code>a</code>. This example demonstrates
some common XPath expressions for selecting elements based on the
document root. For examples of XPath expressions relative to a
particular node, see <a href="../org.w3c.dom/xpath_GetRelElem.html" class="eglink"><font size="-1"><b>eX</b> X</font></a>. For
more information about XPath, see the specification at
<a href="http://www.w3c.org/TR/xpath"><font size="-1">http://www.w3c.org/TR/xpath</font></a>.
The XPath package used in this example selects nodes in a DOM
document. Hence, the XML file is first parsed into a DOM document and
the XPath expression is then applied to the DOM document. 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 this
example.
<P> Note: This example uses the XPath packages (<code>org.apache.xpath.*</code>)
available in J2SE 1.4. However, these packages are not yet part of
the Java 2 API and so this example may not work in future versions of
J2SE.
<pre>
// Get the root element (without specifying its name)
String xpath = "/*"; // 1
// Get the root element (using its name)
xpath = "/root"; // 1
// Get all elements directly under the root
xpath = "/root/*"; // 2 8 12
// Get all e elements directly under the root
xpath = "/root/e"; // 12
// Get all e elements in the document
xpath = "//e"; // 4 6 10 11 12
// Get all non-e elements in the document
xpath = "//*[name() != 'e']"; // 1 2 3 5 7 8 9
// Get all e elements directly under an elem1 element
xpath = "//elem1/e"; // 10 11
// Get all e elements anywhere under an elem1 element
xpath = "//elem1//e"; // 4 6 10 11
// Get all elements with at least one child element
xpath = "//*[*]"; // 1 2 3 5 8
// Get all elements without a child element
xpath = "//*[not(*)]"; // 4 6 7 9 10 11 12
// Get all elements with at least one child e element
xpath = "//*[e]"; // 1 3 5 8
// Get all elements with more than one child e elements
xpath = "//*[count(e)>1]"; // 8
// Get all non-e elements without an e child element
xpath = "//*[not(e) and name() != 'e']"; // 2 7 9
// Get all <font color="#0066ff"><i>level-4</i></font> e elements (the root being at level 1)
xpath = "/*/*/*/e"; // 4
// Get all elements with more than one child e elements
xpath = "//*[count(e)>1]"; // 8
</pre>
XPath 1.0 does not support regular expressions to match element names.
However, it is possible to perform some very simple matches on element
names.
<pre>
// Get all elements whose name starts with el
xpath = "//*[starts-with(name(), 'el')]"; // 2 3 5 7 8 9
// Get all elements whose name contains with lem1
xpath = "//*[contains(name(), 'lem1')]"; // 2 8
</pre>
Sets of elements can also be combined using the union operator <code>|</code>
<pre>
// Get all e elements directly under either the root or an elem2 element
xpath = "/*/e | //elem2/e"; // 4 12
</pre>
Elements are returned in <font color="#0066ff"><i>document order</i></font> - that is, if the
location of <code>A</code>'s start tag appears before the location of <code>B</code>'s
start tag in the XML document, element <code>A</code> is returned before
element <code>B</code>. Moreover, the returned elements are unique.
<pre>
// Read an XML document; this method is implemented in
// <a href="../javax.xml.parsers/BasicDom.html" class="eglink"><font size="-1"><b>e510</b> The Quintessential Program to Create a DOM Document from an XML File</font></a>
Document doc = <font color="#0066ff"><i>parseXmlFile</i></font>(<font color="#0066ff"><i>"infilename.xml"</i></font>, <font color="#0066ff"><i>false</i></font>);
try {
// Get the matching elements
NodeList nodelist = org.apache.xpath.XPathAPI.selectNodeList(doc, xpath);
// Process the elements in the nodelist
for (int i=0; i<nodelist.getLength(); i++) {
// Get element
Element elem = (Element)nodelist.item(i);
}
} catch (javax.xml.transform.TransformerException e) {
}
</pre>
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>
<P><table width="600" CELLSPACING="0" CELLPADDING="2" BORDER="0">
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Related Examples
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e549. <a class="eglink" href="xpath_GetChildElem.html?l=rel">
Selecting from a Set of Child Elements 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>
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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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