Use of "ancestor" in XPath expression
As you learned about descendant axis in XPath
expression in the previous example, this section will illustrate the use
of ancestor in XPath expression. "ancestor" selects
parent element or ancestor of the context node and super-parent of that parent.
In this example we have created an XML file "persons.xml"
as in our previous section, which is necessary to execute XPath query on
to it. This "persons.xml" contains information related to name,
age, gender of different persons.
Here is the full source code for persons.xml file
as follows :
persons.xml
<?xml version="1.0" ?>
<information>
<person id="1">
<name>Deep</name>
<age>34</age>
<gender>Male</gender>
</person>
<person id="2">
<name>Kumar</name>
<age>24</age>
<gender>Male</gender>
</person>
<person id="3">
<name>Deepali</name>
<age>19</age>
<gender>Female</gender>
</person>
<!-- more persons... -->
</information> |
Now we have declared a class XPathAncestor class
and
in this class we are parsing the XML file with JAXP. First of all we need
to load the document into DOM Document object. We have put that
persons.xml file in that current working directory.
DocumentBuilderFactory domFactory =
DocumentBuilderFactory.newInstance();
domFactory.setNamespaceAware(true);
DocumentBuilder builder = domFactory.newDocumentBuilder();
Document doc = builder.parse("persons.xml"); |
Above lines of code parses "persons.xml"
file and creates a Document object. Next we have created XPath object
with the use of XPathFactory.
XPath xpath = XPathFactory.newInstance().newXPath(); |
XPath expression "//person/ancestor::*" will
select parent or ancestor of person as well as ancestor of person.
Here is full example code for XPathAncestor.java
as follows:
XPathAncestor.java
import org.w3c.dom.*;
import javax.xml.xpath.*;
import javax.xml.parsers.*;
import java.io.IOException;
import org.xml.sax.SAXException;
public class XPathAncestor {
public static void main(String[] args)
throws ParserConfigurationException, SAXException,
IOException, XPathExpressionException {
DocumentBuilderFactory domFactory =
DocumentBuilderFactory.newInstance();
domFactory.setNamespaceAware(true);
DocumentBuilder builder = domFactory.newDocumentBuilder();
Document doc = builder.parse("persons.xml");
XPath xpath = XPathFactory.newInstance().newXPath();
XPathExpression expr = xpath.compile("//person/ancestor::*");
// Selecting person element ancestor's name
Object result = expr.evaluate(doc, XPathConstants.NODESET);
NodeList nodes = (NodeList) result;
for (int i = 0; i < nodes.getLength(); i++) {
System.out.println(nodes.item(i).getNodeName());
}
expr = xpath.compile("//ancestor::name/text()");
// Selecting name element ancestor's value
result = expr.evaluate(doc, XPathConstants.NODESET);
nodes = (NodeList) result;
for (int i = 0; i < nodes.getLength(); i++) {
System.out.print(nodes.item(i).getNodeValue()+", ");
}
System.out.println();
expr = xpath.compile("//ancestor::age/text()");
// Selecting age element ancestor's value
result = expr.evaluate(doc, XPathConstants.NODESET);
nodes = (NodeList) result;
for (int i = 0; i < nodes.getLength(); i++) {
System.out.print(nodes.item(i).getNodeValue()+", ");
}
System.out.println();
}
}
|
Output:
Download Source Code
