Namespance prefix transparent XPath lookup

[Chetan Parekh]

Our application is receiving data in a form of XML files from multiple sources. We are extracting some field values from these XML file using XPath and populating in the database.
The XML files we are receiving are having different prefix for the same namespace. Our XPath code is capable of performing lookup based on any one prefix.

How to perform XPath lookup which is prefix transparent?

<?xml version="1.0" encoding="UTF-8"?>
<tns:STUDENT
	xmlns:tns="http://www.abc.com/Student/1.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://www.abc.com/Student/1.0 Student.xsd ">
	<tns:ROLLNO >1</tns:ROLLNO>
	<tns:FIRST_NAME>Chetan</tns:FIRST_NAME>
	<tns:LAST_NAME>Parekh</tns:LAST_NAME>
</tns:STUDENT>

<?xml version="1.0" encoding="UTF-8"?>
<ns1:STUDENT
	xmlns:ns1="http://www.abc.com/Student/1.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://www.abc.com/Student/1.0 Student.xsd ">
	<ns1:ROLLNO >1</ns1:ROLLNO>
	<ns1:FIRST_NAME>Chetan</ns1:FIRST_NAME>
	<ns1:LAST_NAME>Parekh</ns1:LAST_NAME>
</ns1:STUDENT>

import java.util.Iterator;

import javax.xml.namespace.NamespaceContext;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathFactory;

import org.apache.xml.utils.PrefixResolver;
import org.apache.xml.utils.PrefixResolverDefault;
import org.w3c.dom.Document;

public class App {
	public static void main(String[] args) {
		try {
			
			/**
			 * 
			 */
			DocumentBuilderFactory domFactory = DocumentBuilderFactory
					.newInstance();
			domFactory.setNamespaceAware(true);
			DocumentBuilder builder = domFactory.newDocumentBuilder();
			Document doc = builder.parse("NewXMLSchema.xml");

			/**
			 * 
			 */
			final PrefixResolver resolver = new PrefixResolverDefault(
					doc.getDocumentElement());
			NamespaceContext ctx = new NamespaceContext() {
				public String getNamespaceURI(String prefix) {
					return resolver.getNamespaceForPrefix(prefix);
				}

				public Iterator getPrefixes(String val) {
					return null;
				}
				public String getPrefix(String uri) {
					return null;
				}
			};


			/**
			 * 
			 */
			String xpathStr = "//ns1:STUDENT/ns1:ROLLNO/text()";
			XPathFactory xpathFact = XPathFactory.newInstance();
			XPath xpath = xpathFact.newXPath();
			xpath.setNamespaceContext(ctx);
			String result = xpath.evaluate(xpathStr, doc);
			System.out.println("XPath result is \"" + result + "\"");
		} catch (Exception ex) {
			ex.printStackTrace();
		}
	}
}

[g tsuji]

The situation is like this. The prefix for binding to a non-null namespace in the xpath is quite arbitrary in nature as long as the uri bound to it is the proper namespace uri. However, working with team or alone, it is sometimes---if not you, it may be some of your colleagues---very tempting to use the same as appeared in the xml document. Hence, it is of no harm to put the possible prefixes used in the incoming xml inside a lookup table if not just as a reminder. Besides, you can use some "universal" prefix (say "s10", as long as it won't possible appear in the xml as prefix for some other namespace) specifically binding to the .../Student/1.0 namespace at the consumer-side, that is agreed upon amongst the dev team or yourself.

Hence, if I capture the essential of what you've meant by transparent, you can do this in the NamespaceContent handling.

public String getNamespaceURI(String prefix) {
    //return resolver.getNamespaceForPrefix(prefix);
    if (null != resolver.getNamespaceForPrefix(prefix)) {
        return resolver.getNamespaceForPrefix(prefix);
    } else {
        //this is the lookup table proper
        if ("ns1".equals(prefix)) return "http://www.abc.com/Student/1.0";
        if ("tns".equals(prefix)) return "http://www.abc.com/Student/1.0";
        //some universal prefix for ...Student/1.0 namespace uri
        if ("s10".equals(prefix)) return "http://www.abc.com/Student/1.0";
        //if nothing matched, return some default namespace
        //(for this, you need add an import javax.xml.XMLConstant;)
        return resolver.getNamespaceForPrefix(XMLConstants.DEFAULT_NS_PREFIX);
        //actually someother return can be conceived such as 
        //return XMLConstant.NULL_NS_URI;
        //but in any cas you would more often than not in trouble arriving here
    }
}

That's the idea. After that, you can use tns or ns1 or the fixed s01 as prefix in the xpath for the targetted namespace to bind to.