bea.com | products | dev2dev | support | askBEA |
|
e-docs > WebLogic Server > Programming WebLogic XML > Using the WebLogic XPath API |
Programming WebLogic XML |
The following sections provide information about the WebLogic XPath API:
Overview of the WebLogic XPath API
The WebLogic XPath API contains all of the classes required to perform XPath matching against a document represented as a DOM, XMLNode, or against an XMLInputStream. Use the API if you want to identify a subset of XML elements within an XML document that conform to a given pattern.
For additional API reference information about the WebLogic XPath API, see the weblogic.xml.xpath Javadoc.
This section describes how to use the DOMXPath class of the WebLogic XPath API to perform XPath matching against an XML document represented as a DOM. The section first provides an example and then a description of the main steps used in the example.
Example of Using the DOMXPath Class
The sample Java program at the end of this section uses the following XML document in its matching:
<?xml version='1.0' encoding='us-ascii'?>
<!-- "Purchaseorder". -->
<purchaseorder
department="Sales"
date="01-11-2001"
raisedby="Picachu"
>
<item
ID="101">
<title>Laptop</title>
<quantity>5</quantity>
<make>Dell</make>
</item>
<item
ID="102">
<title>Desktop</title>
<quantity>15</quantity>
<make>Dell</make>
</item>
<item
ID="103">
<title>Office Software</title>
<quantity>10</quantity>
<make>Microsoft</make>
</item>
</purchaseorder>
The Java code example is as follows:
package examples.xml.xpath;
import java.io.IOException;
import java.util.Iterator;
import java.util.Set;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.xml.sax.SAXException;
import weblogic.xml.xpath.DOMXPath;
import weblogic.xml.xpath.XPathException;
/**
* This class provides a simple example of how to use the DOMXPath
* API.
*
* @author Copyright (c) 2002 by BEA Systems, Inc. All Rights Reserved.
*/
public abstract class DOMXPathExample {
public static void main(String[] ignored)
throws XPathException, ParserConfigurationException,
SAXException, IOException
{
// create a dom representation of the document
String file = "purchaseorder.xml";
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(true); // doesn't matter for this example
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(file);
// create some instances of DOMXPath to evaluate against the
// document.
DOMXPath totalItems = // count number of items
new DOMXPath("count(purchaseorder/item)");
DOMXPath atLeast10 = // titles of items with quantity >= 10
new DOMXPath("purchaseorder/item[quantity >= 10]/title");
// evaluate them against the document
double count = totalItems.evaluateAsNumber(doc);
Set nodeset = atLeast10.evaluateAsNodeset(doc);
// output results
System.out.println(file+" contains "+count+" total items.");
System.out.println("The following items have quantity >= 10:");
if (nodeset != null) {
Iterator i = nodeset.iterator();
while(i.hasNext()) {
Node node = (Node)i.next();
System.out.println(" "+node.getNodeName()+
": "+node.getFirstChild().getNodeValue());
}
}
// note that at this point we are free to continue using evaluate
// atLeast10 and totalItems against other documents
}
}
Main Steps When Using the DOMXPath Class
The following procedure describes the main steps to use the DOMXPath class to perform XPath matching against an XML document represented as a DOM:
String file = "purchaseorder.xml";
DocumentBuilderFactory factory =
DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(file);
The following example shows an XPath expression that counts the items in a purchase order:
DOMXPath totalItems =
new DOMXPath("count(purchaseorder/item)");
The following example shows an XPath expression that returns the titles of items whose quantity is greater or equal to 10:
DOMXPath atLeast10 =
new DOMXPath("purchaseorder/item[quantity >= 10]/title");
The following example shows how to use the evaluateAsNumber() method to evaluate the totalItems XPath expression:
double count = totalItems.evaluateAsNumber(doc);
System.out.println(file+" contains "+count+" total items.");
The following example shows how to use the evaluateAsNodeset() method to return a Set of org.w3c.dom.Nodes which you can iterate through in the standard way:
Set nodeset = atLeast10.evaluateAsNodeset(doc);
System.out.println("The following items have quantity >= 10:");
if (nodeset != null) {
Iterator i = nodeset.iterator();
while(i.hasNext()) {
Node node = (Node)i.next();
System.out.println(" "+node.getNodeName()+
": "+node.getFirstChild().getNodeValue());
}
}
For additional API reference information about the WebLogic XPath API, see the weblogic.xml.xpath Javadoc.
The example in this section shows how to use the StreamXPath class of the WebLogic XPath API to perform XPath matching against an XMLInputStream. The section first provides an example and then a description of the main steps used in the example.
Example of Using the StreamXPath Class
The sample Java program at the end of this section uses the following XML document in its matching:
<?xml version='1.0' encoding='us-ascii'?>
<!-- "Stock Quotes". -->
<stock_quotes>
<stock_quote symbol='BEAS'>
<when>
<date>01/27/2001</date>
<time>3:40PM</time>
</when>
<price type="ask" value="65.1875"/>
<price type="open" value="64.00"/>
<price type="dayhigh" value="66.6875"/>
<price type="daylow" value="64.75"/>
<change>+2.1875</change>
<volume>7050200</volume>
</stock_quote>
<stock_quote symbol='MSFT'>
<when>
<date>01/27/2001</date>
<time>3:40PM</time>
</when>
<price type="ask" value="55.6875"/>
<price type="open" value="50.25"/>
<price type="dayhigh" value="56"/>
<price type="daylow" value="52.9375"/>
<change>+5.25</change>
<volume>64282200</volume>
</stock_quote>
</stock_quotes>
The Java code for the example is as follows:
package examples.xml.xpath;
import java.io.File;
import weblogic.xml.stream.Attribute;
import weblogic.xml.stream.StartElement;
import weblogic.xml.stream.XMLEvent;
import weblogic.xml.stream.XMLInputStream;
import weblogic.xml.stream.XMLInputStreamFactory;
import weblogic.xml.stream.XMLStreamException;
import weblogic.xml.xpath.StreamXPath;
import weblogic.xml.xpath.XPathException;
import weblogic.xml.xpath.XPathStreamFactory;
import weblogic.xml.xpath.XPathStreamObserver;
/**
* This class provides a simple example of how to use the StreamXPath
* API.
*
* @author Copyright (c) 2002 by BEA Systems, Inc. All Rights Reserved.
*/
public abstract class StreamXPathExample {
public static void main(String[] ignored)
throws XPathException, XMLStreamException
{
// Create instances of StreamXPath for two xpaths we want to match
// against this tream.
StreamXPath symbols =
new StreamXPath("stock_quotes/stock_quote");
StreamXPath openingPrices =
new StreamXPath("stock_quotes/stock_quote/price[@type='open']");
// Create an XPathStreamFactory.
XPathStreamFactory factory = new XPathStreamFactory();
// Create and install two XPathStreamObservers. In this case, we
// just use to anonymous classes to print a message when a
// callback is received. Note that a given observer can observe
// more than one xpath, and a given xpath can be observed by
// mutliple observers.
factory.install(symbols, new XPathStreamObserver () {
public void observe(XMLEvent event) {
System.out.println("Matched a quote: "+event);
}
public void observeAttribute(StartElement e, Attribute a) {} //ignore
public void observeNamespace(StartElement e, Attribute a) {} //ignore
});
// Note that we get matches for both a start and an end elements,
// even in the case of <price/> which is an empty element - this
// is the behavior of the underlying streaming parser.
factory.install(openingPrices, new XPathStreamObserver () {
public void observe(XMLEvent event) {
System.out.println("Matched an opening price: "+event);
}
public void observeAttribute(StartElement e, Attribute a) {} //ignore
public void observeNamespace(StartElement e, Attribute a) {} //ignore
});
// get an XMLInputStream on the document
String file = "stocks.xml";
XMLInputStream sourceStream = XMLInputStreamFactory.newInstance().
newInputStream(new File(file));
// use the factory to create an XMLInputStream that will do xpath
// matching against the source stream
XMLInputStream matchingStream = factory.createStream(sourceStream);
// now iterate through the stream
System.out.println("Matching against xml stream from "+file);
while(matchingStream.hasNext()) {
// we don't do anything with the events in our example - the
// XPathStreamObserver instances that we installed in the
// factory will get call backs for appropriate events
XMLEvent event = matchingStream.next();
}
}
}
Main Steps When Using the StreamXPath Class
The following procedure describes the main steps to use the StreamXPath class to perform XPath matching against an XML document represented as an XMLInputStream:
The following example shows an XPath expression that searches for stock quotes in an XML document:
StreamXPath symbols =
new StreamXPath("stock_quotes/stock_quote");
The following example shows an XPath expression that matches stock quotes using their opening price:
StreamXPath openingPrices = new StreamXPath("stock_quotes/stock_quote/price[@type='open']");
XPathStreamFactory factory = new XPathStreamFactory();
factory.install(symbols, new XPathStreamObserver () {
public void observe(XMLEvent event) {
System.out.println("Matched a quote: "+event);
}
public void observeAttribute(StartElement e, Attribute a) {}
public void observeNamespace(StartElement e, Attribute a) {}
}
);
String file = "stocks.xml";
XMLInputStream sourceStream =
XMLInputStreamFactory.newInstance().newInputStream(new File(file));
XMLInputStream matchingStream =
factory.createStream(sourceStream);
while(matchingStream.hasNext()) {
XMLEvent event = matchingStream.next();
}
For additional API reference information about the WebLogic XPath API, see the weblogic.xml.xpath Javadoc.