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<TITLE>Finding Elements by Id 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" class="xsmall-font">
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<h3>e1077. Finding Elements by Id 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"><b>e1074</b> Finding Elements by Absolute Location in a DOM Document Using XPath</a> for common XPath
expression for selecting elements. This example adds to those
examples by demonstrating the ability to select elements based on their
id.
<P> The DTD of an XML file may declare that a certain attribute of
an element is a <font color="#0066ff"><i>unique id</i></font>. An attribute designated as such can
contain any value but no two id attributes can have the same value.
<P> This example demonstrates some common uses of expressions that
use element ids; for more information on XPath, see the specification
at <a href="http://www.w3c.org/TR/xpath">http://www.w3c.org/TR/xpath</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 element id 3
String xpath = "id('3')"; // 3
// Get all e elements directly under element id 3
xpath = "id('two')/e"; // 3 4 6
// Get elements with id='two', id='3', or id='seven'
xpath = "id('two 3 seven the fifth')"; // two 3 seven
// Note that this method of finding elements does not work
// if the id value contains a space
// Get a non-existent element
xpath = "id('100')"; // (none)
</pre>
To execute an XPath expression, see
<a href="../org.w3c.dom/xpath_GetAbsElem.html" class="eglink"><b>e1074</b> Finding Elements by Absolute Location in a DOM Document Using XPath</a>. Here is the sample XML file
used in the example:
<pre> <?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE root [ <!ELEMENT e (e*) >
<!ATTLIST e id ID #REQUIRED>
]>
<root>
<e id="1">
<e id="two">
<e id="3"/>
<e id="4">
<e id="the fifth"/>
</e>
<e id="6"/>
</e>
</e>
<e id="seven"/>
</root>
</pre>
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<b>Related Examples</b></font></td>
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e1074. <a class="eglink" href="xpath_GetAbsElem.html?l=rel">
Finding Elements by Absolute Location in a DOM Document Using XPath
</a>
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e1075. <a class="eglink" href="xpath_GetChildElem.html?l=rel">
Selecting from a Set of Child Elements in a DOM Document Using XPath
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e1076. <a class="eglink" href="xpath_GetElemByText.html?l=rel">
Finding Elements by Content in a DOM Document Using XPath
</a>
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e1078. <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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