XPathEvaluator namespace prefix issues

[Richard Zschech]

Hi,

I'm having a problem using the org.apache.xpath.domapi.XPathEvaluatorImpl with namespace prefixes in my xpath expression.
An example xpath I have is "dyn:map(., '.')" which dosent do much but it relies on the exslt extensions.

I have made a custom namespace resolver which maps the standard exslt prefixes to their namespaces and a test program as follows:




import java.io.StringReader;
import org.xml.sax.InputSource;

import org.w3c.dom.Node;
import org.w3c.dom.Document;
import org.w3c.dom.xpath.XPathResult;
import org.w3c.dom.xpath.XPathException;
import org.w3c.dom.xpath.XPathEvaluator;
import org.w3c.dom.xpath.XPathExpression;
import org.w3c.dom.xpath.XPathNSResolver;

import javax.xml.parsers.DocumentBuilderFactory;

// Need to extend org.apache.xpath.domapi.XPathNSResolverImpl to prevent class casts in the xpath evaluator
public class XPathTest extends org.apache.xpath.domapi.XPathNSResolverImpl implements XPathNSResolver {
public static void main(String[] args) throws Exception {
org.apache.xalan.Version.main(null);
XPathEvaluator xpathEvaluator = new org.apache.xpath.domapi.XPathEvaluatorImpl();
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
documentBuilderFactory.setNamespaceAware(true);
Document doc = documentBuilderFactory.newDocumentBuilder().parse(new InputSource(new StringReader("<foo/>")));
try {
System.out.println("Trying with no namespace resolver");
Object result = xpathEvaluator.evaluate("dyn:map(., '.')", doc, null, XPathResult.ANY_TYPE, null);
System.out.println(result);
}
catch(Exception e) {
System.out.println("I expected this to fail");
e.printStackTrace();
}

try {
System.out.println();
System.out.println("Trying with my namespace resolver");
Object result = xpathEvaluator.evaluate("dyn:map(., '.')", doc, new XPathTest(), XPathResult.ANY_TYPE, null);
System.out.println(result);
}
catch(Exception e) {
System.out.println("I cant work out why this failed");
e.printStackTrace();
}
}
private XPathTest() {
super(null);
}
// these methods are the ones called by the xpath engine
public String getNamespaceForPrefix(String prefix) {
return lookupNamespaceURI(prefix);
}
public String getNamespaceForPrefix(String prefix, Node namespaceContext) {
return lookupNamespaceURI(prefix);
}
// do the actual namespace lookup
public String lookupNamespaceURI(String prefix) {
System.out.println("lookupNamespaceURI " + prefix);
if(prefix.equals("date")) {
return "http://exslt.org/dates-and-times";;
}
else if(prefix.equals("dyn")) {
return "http://exslt.org/dynamic";;
}
else if(prefix.equals("exsl")) {
return "http://exslt.org/common";;
}
else if(prefix.equals("func")) {
return "http://exslt.org/functions";;
}
else if(prefix.equals("math")) {
return "http://exslt.org/math";;
}
else if(prefix.equals("regexp")) {
return "http://exslt.org/regular-expressions";;
}
else if(prefix.equals("set")) {
return "http://exslt.org/sets";;
}
else if(prefix.equals("str")) {
return "http://exslt.org/strings";;
}
else {
return null;
}
}
}



I try to evaluate the xpath with no name space resolver and it fails as expected:


Trying with no namespace resolver
I expected this to fail
org.w3c.dom.DOMException: Unable to resolve prefix with null prefix resolver.
at org.apache.xpath.domapi.XPathEvaluatorImpl$DummyPrefixResolver.getNamespaceForPrefix(XPathEvaluatorImpl.java:115)
at org.apache.xpath.domapi.XPathEvaluatorImpl$DummyPrefixResolver.getNamespaceForPrefix(XPathEvaluatorImpl.java:125)
at org.apache.xpath.compiler.Lexer.mapNSTokens(Lexer.java:625)
at org.apache.xpath.compiler.Lexer.tokenize(Lexer.java:303)
at org.apache.xpath.compiler.Lexer.tokenize(Lexer.java:134)
at org.apache.xpath.compiler.XPathParser.initXPath(XPathParser.java:155)
at org.apache.xpath.XPath.<init>(XPath.java:202)
at org.apache.xpath.XPath.<init>(XPath.java:238)
at org.apache.xpath.domapi.XPathEvaluatorImpl.createExpression(XPathEvaluatorImpl.java:199)
at org.apache.xpath.domapi.XPathEvaluatorImpl.evaluate(XPathEvaluatorImpl.java:291)
at XPathTest.main(XPathTest.java:30)


Then with my namespace resolver:

Trying with my namespace resolver
lookupNamespaceURI dyn
I cant work out why this failed
org.w3c.dom.xpath.XPathException: Unknown error in XPath
at org.apache.xpath.domapi.XPathExpressionImpl.evaluate(XPathExpressionImpl.java:208)
at org.apache.xpath.domapi.XPathEvaluatorImpl.evaluate(XPathEvaluatorImpl.java:293)
at XPathTest.main(XPathTest.java:41)


In my actual usage rather then the test above I have also got the following probably related exception:

org.w3c.dom.xpath.XPathException: java.lang.NoSuchMethodException: For extension function, could not find method org.apache.xpath.axes.WalkingIterator.map([ExpressionContext,] #STRING).
at org.apache.xpath.domapi.XPathExpressionImpl.evaluate(XPathExpressionImpl.java:208)
at org.apache.xpath.domapi.XPathEvaluatorImpl.evaluate(XPathEvaluatorImpl.java:293)

Im guessing the xpath engine is looking in the wrong class for the map method.


Do I need to do any more to set up the org.apache.xpath.domapi.XPathEvaluatorImpl object before calling the evaluate method with the correct namespace resolver?

Thanks for any help in advance,

From Richard.