Use of "preceding" axis in XPath expression
In this part of tutorial we are going to describe you
the use of "preceding" axis in XPath expression. "preceding"
axis will select each and every element or node before the given context
node.
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> |
We have put that
persons.xml file in that current working directory. Now we have declared a class
XPathPreceding 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.
DocumentBuilderFactory domFactory =
DocumentBuilderFactory.newInstance();
domFactory.setNamespaceAware(true);
DocumentBuilder builder = domFactory.newDocumentBuilder();
Document doc = builder.parse("persons.xml"); |
For downloading document we have created a new instance
of DocumentBuilderFactory and then this instance is further going to be
used in creating an object of DocumentBuilder. "setNamespaceAware()"
tells that the parser produced by this code will provide full support for XML
namespaces. 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/preceding::*"
will select all elements that are before the
start of the context node.
Here is the example code for XPathPreceding.java
as follows:
XPathPreceding.java
import org.w3c.dom.*;
import javax.xml.xpath.*;
import javax.xml.parsers.*;
import java.io.IOException;
import org.xml.sax.SAXException;
public class XPathPreceding {
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/preceding::*");
// Selecting person element's preceding elements 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("//person/preceding::*/name/text()");
// Selecting all person element's precding elements values
result = expr.evaluate(doc, XPathConstants.NODESET);
nodes = (NodeList) result;
for (int i = 0; i < nodes.getLength(); i++) {
System.out.print(nodes.item(i).getNodeValue()+", ");
}
}
}
|
Output:
Download Source Code