Parsing XML file using Xpath in jdk1.4

[O. Ziggy]

I found the following easy solution to extracting values from XML file.

import java.io.IOException;
import org.w3c.dom.*;
import org.xml.sax.SAXException;
import javax.xml.parsers.*;
import javax.xml.xpath.*;

public class XPathExample {

  public static void main(String[] args) 
   throws ParserConfigurationException, SAXException, 
          IOException, XPathExpressionException {

    DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
    domFactory.setNamespaceAware(true); // never forget this!
    DocumentBuilder builder = domFactory.newDocumentBuilder();
    Document doc = builder.parse("c:\\temp\\books.xml");

    XPathFactory factory = XPathFactory.newInstance();
    XPath xpath = factory.newXPath();
    XPathExpression expr 
     = xpath.compile("//book[author='Neal Stephenson']/title/text()");

    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).getNodeValue()); 
    }

  }

}

This uses xpath to extract all books title where the author is Neal Stephenson from the following xml

<inventory>
<book year="2000">
    <title>Snow Crash</title>
    <author>Neal Stephenson</author>
    <publisher>Spectra</publisher>
    <isbn>0553380958</isbn>
    <price>14.95</price>
</book>

<book year="2005">
    <title>Burning Tower</title>
    <author>Larry Niven</author>
    <author>Jerry Pournelle</author>
    <publisher>Pocket</publisher>
    <isbn>0743416910</isbn>
    <price>5.99</price>
</book>

<book year="1995">
    <title>Zodiac</title>
    <author>Neal Stephenson</author>
    <publisher>Spectra</publisher>
    <isbn>0553573862</isbn>
    <price>7.50</price>
</book>

<!-- more books... -->

</inventory>

Now this works fine on JDK5 but i am using jdk 1.4 Can this be converted to the java 1.4 equivalent?

All i am trying to do is extract a value from an xml element. For example, in the above xml, i just want something that is the equivalent of getElementByTag("title").

Thanks

[Sunny Bhandari]

You need to include third party libraries for XML parsing if you are using JDK 1.4...

[Ulf Dittmer]

Sunny Bhandari wrote:You need to include third party libraries for XML parsing if you are using JDK 1.4...

Not XML parsing libraries as such (Java 1.4 has those), just an XPath library - like Jaxen.

[O. Ziggy]

Is it not possible to parse XML in 1.4?

[Ulf Dittmer]

O. Ziggy wrote:Is it not possible to parse XML in 1.4?

Of course it is - Java 1.4 has full support for DOM and SAX built in. What it does not have built in is support for XPath (that was introduced in Java 5). That shouldn't be a surprise since XPath was finalized after the Java 1.4 API was finalized. Jaxen does a fine job of implementing XPath, although -obviously- with an API other than javax.xml.xpath.

But Java 1.4 was marked obsolete quite a few years ago, so it's to be expected that these days you need to go to some hassle to support it.

[O. Ziggy]

Ok thanks Ulf. I'll have a look at Jaxen.

[O. Ziggy]

I am trying to understand parsing in XML but it is quite difficult. The problem i have is that i am working with JDK1.4 and i am trying to parse an xml file using xpath.
Having looked around i cant work out whether xpath is possible in JDK1.4 or not.

I must admit i dont quite understand the whole XML processing architectures. There seems to be quite a lot of libraries, API that is resulting in my brain being overloaded.

From what i have read, to be able to use XPATH i need JAXP. Some articles say that JAXP is included in JDK1.4 and some say it is not. is it?

I tried running the following code and it didnt work in 1.4 but does work in 1.5

import java.io.IOException;
import org.w3c.dom.*;
import org.xml.sax.SAXException;
import javax.xml.parsers.*;
import javax.xml.xpath.*;

public class XPathExample {

  public static void main(String[] args) 
   throws ParserConfigurationException, SAXException, 
          IOException, XPathExpressionException {

    DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
    domFactory.setNamespaceAware(true); // never forget this!
    DocumentBuilder builder = domFactory.newDocumentBuilder();
    Document doc = builder.parse("c:\\temp\\books.xml");

    XPathFactory factory = XPathFactory.newInstance();
    XPath xpath = factory.newXPath();
    XPathExpression expr 
     = xpath.compile("//book[author='Neal Stephenson']/title/text()");

    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).getNodeValue()); 
    }

  }

}

Having read further i found that JAXP can be downloaded separately. But the problem i found is that there are so many variants of it.
I did download one of the variants, i.e. http://jaxp.java.net/downloads.html. This gave me to library files

jaxp-api.jar
jaxp.ri.jar

I tried the same code with the above libraries in the class path and it seems to have compile successfully but when i run it it just terminates.

I guess i need to take a step back and understand what i am doing.

- What do i need to do to be able to parse an xml file using xpath *in jdk1.4*
- Is there a resource that can help in understanding xml processing (i.e. the difference in JAXP, JDOM, XPATH, xalan, xerces etc)

[Ulf Dittmer]

What do i need to do to be able to parse an xml file using xpath *in jdk1.4*

As I said, the Jaxen library can do that, but it has its own API - NOT javax.xml.xpath.

The JAXP package you downloaded can be made to work with Java 1.4, but you need to resort to some trickery which I would not recommend for production systems. Jaxen really is the better choice.

If you insist on using the javax.xml.xpath API, then you need to convince your JVM to use those jar files instead of its own built-in classes. You can either a) copy jaxp-api.jar and jaxp.ri.jar to <java-home>/lib/endorsed where <java-home> refers to the directory where the runtime software is installed (which is the top-level directory of the J2SE Runtime Environment or the jre directory in the JDK), or b) if you prefer not to change the JRE, you can start the JVM with the -Djava.endorsed.dirs=%JAXP% switch, where JAXP should point to the directory that contains those jar files.

Is there a resource that can help in understanding xml processing (i.e. the difference in JAXP, JDOM, XPATH, xalan, xerces etc)

Start with the XmlFaq. It links to lots of good material, including introductory articles on the topics you asked about, and to the https://coderanch.com/how-to/java/XmlLinks page which links to even more stuff.

[O. Ziggy]

Ok i am trying this with JDOM which i believe uses Jaxen.

I am trying to parse the same xml file using the following code

import java.io.FileInputStream;
import java.io.IOException;
import java.util.Iterator;
import java.util.List;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.jdom.input.SAXBuilder;
import org.jdom.xpath.XPath;
import org.jdom.Document;
import org.jdom.Element;
import org.xml.sax.SAXException;

public class XPathExample {

  public static void main(String[] args) 
   throws ParserConfigurationException, SAXException, 
          IOException, Exception {
	  
	// import org.jdom.Document;
	// import org.jdom.Element;
	// import org.jdom.JDOMException;
	// import org.jdom.input.SAXBuilder;
	// import org.jdom.xpath.XPath;
	 String fn = "c:\\temp\\books.xml";
	 FileInputStream in = new FileInputStream(fn);
	 SAXBuilder builder = new SAXBuilder();
	 Document doc = builder.build(in);
	 in.close();
	 
	 XPath xpath = XPath.newInstance("//book[author='Neal Stephenson']/title/text()");
	 List list = xpath.selectNodes(doc);
	 for (Iterator iter = list.iterator(); iter.hasNext();) {
	  Element elem = (Element) iter.next();
	   
	  String childText = elem.getChild("child").getTextTrim();
	  String text = elem.getTextTrim();
	  
	  System.out.println("Value : " + text);
	 }	 
  }
}

it is failing with a classcast exception at Element elem = (Element) iter.next();

Any ideas?

[O. Ziggy]

The cast exception is because the xpath expression is asking for the text() node not element node.

Thanks

[Ulf Dittmer]

Element is just one of several object types selectNodes can return. You either need to cast to a specific one (if you're sure that all nodes will be of that type), or test the type using instanceof before casting. I would recommend the latter approach, combined with logging that reports unexpected types.

[O. Ziggy]

I dont actually need the element object i just need to extract the content of the element i am trying to exctract. I changed it to something like this

String title = iter.next();

[Ulf Dittmer]

So all is good now?

[O. Ziggy]

Yes - All thanks to you!
Thanks for the help.

[vtd-xml author]

FYI, the xpath code in vtd-xml (http://vtd-xml.sf.net/)

import com.ximpleware.*; 
public class vtdXPath {
	public static void main(String[] args) throws Exception {		
		VTDGen vg = new VTDGen();		
		if (vg.parseHttpUrl("c:\\xml\\my.xml", true)) {
			VTDNav vn = vg.getNav();
			AutoPilot ap = new AutoPilot();
			ap.selectXPath("//book[author='Neal Stephenson']/title/text()");
			ap.bind(vn);
			int i=-1;
			while ((i = ap.evalXPath()) != -1) {
				System.out.println("Index No. is " + i);
			}
		}
	}
}