XPath 2

[Marco Rossi]

Hi all,

in my application I need to make some queries to an external XML file and I am using XPath.

Java6 (and 7 too) offers support to XPath1.0 but I need to build some complex XPath expressions that only work in XPath 2.

At the moment, this is what I am doing:

import java.io.IOException;

import javax.xml.namespace.QName;
import javax.xml.parsers.*;
import javax.xml.xpath.*;

import org.w3c.dom.Document;
import org.xml.sax.SAXException;

public class XPathReader {
    
    private String xmlFile;
    boolean DOMUpdated = false;
    private Document xmlDocument;
    private XPath xPath; 
    	
    /**
     * Default constructor
     * @param xmlFile String representing XML file to be read
     */
    public XPathReader(String xmlFile) {
    	
    	this.xmlFile = xmlFile;
    	initObjects();
    }
    
    /**
     * This method initiates objects
     */
    private void initObjects(){        
        try {
            xmlDocument = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(xmlFile);
            
            xPath = XPathFactory.newInstance().newXPath();
            
        } catch (IOException ex) {
            ex.printStackTrace();
        } catch (SAXException ex) {
            ex.printStackTrace();
        } catch (ParserConfigurationException ex) {
            ex.printStackTrace();
        }       
    }
    
    /**
     * This method read XML file using expression given as parameter
     * @param expression XPath expression in form of string
     * @param returnType Return type of the expression
     * @return
     */
    public Object read(String expression, QName returnType){
        try {
            XPathExpression xPathExpression = xPath.compile(expression);
            
            return xPathExpression.evaluate(xmlDocument, returnType);
	        
        } catch (XPathExpressionException ex) {
            ex.printStackTrace();
            return null;
        }
    }	
}

What should I use and do if I want to switch to XPath?

Thanks
Marco

[Wouter Oet]

I think you'll need to find an implementation which supports Xpath 2.0 queries.

[Ulf Dittmer]

The Saxon library supports XPath 2.0. I wouldn't hold my breath for either Jaxen or Xalan to support it, not for it to become part of the standard class libraries.

[Marco Rossi]

I am trying with Saxon but I do not find any good examples...

is it enough to do that?

XPathFactoryImpl xPath = new XPathFactoryImpl();

where XPathFactoryImpl() is net.sf.saxon.xpath.XPathFactoryImpl;

but what about XPathExpression?

XPathExpression xPathExpression = xPath.newXPath().compile(expression);

[g tsuji]

>I am trying with Saxon but I do not find any good examples...
I can give you a complete working demo with null xml document. It tests xpath 2.0 specific suppoted function. I would expect you say "good". It still takes effort to do test or anything at all for that matter.

[0] Add saxon9j.jar and saxon9.jar and saxon9-xpath.jar. (Or some other version, if applicable.)

[1] Only one specific saxon related import statement you need to add (among other according to need.)

import net.sf.saxon.om.NamespaceConstant;

(Not even need if you tolerate writing out the full package.)

[2] This is the method to be called upon in the test program.

void doTest() throws Exception {
		
    String sxpath="current-time()";    //xpath 2.0 function; this provides a clean demo of xpath 2.0 support

    String objectModel = NamespaceConstant.OBJECT_MODEL_SAXON;
    System.setProperty("javax.xml.xpath.XPathFactory:"+objectModel, "net.sf.saxon.xpath.XPathFactoryImpl");
    
    XPathFactory xpathFactory=XPathFactory.newInstance(objectModel);
    XPath xpath = xpathFactory.newXPath();
		
    XPathExpression expr=xpath.compile(sxpath);
    String result = (String)expr.evaluate(null, XPathConstants.STRING);    //null document
    System.out.println("<root>");
    System.out.println("\t<result>"+result+"</result>");
    System.out.println("</root>");
}

[Marco Rossi]

I tried to execute an XPath 2.0 Expression and it works.
What I have done is simply (I found this code on another website):

XPathFactory xPath = new XPathFactoryImpl();

Your way and mine are similar, by the way.

I tried with your implementation and my application works fine too, thanks.

Marco