Weird behavior of XPath.evaluate()

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Weird behavior of XPath.evaluate()

Weird behavior of XPath.evaluate()

2007-05-10 - By Jason Morris

Reply: 1 2 3 4

Hi all,

Apologies if this has been asked before but it is driving me mad. I am
happily able to evaluate non-namespaced XPath expressions using either an
InputSource or a document context element. I can evaluate namespaced
expressions using the InputSource, but it doesn't work if I evaluate a
namespaced expression passing an Element as a context node.

Take the example file from
http://xml.apache.org/xalan-j/xpath_apis.html#namespacecontext

<?xml version='1.0'?>

<foo:document xmlns:foo="http://apache.org/foo" xmlns:bar="
http://apache.org/bar">
<bar:element>MyBar</bar:element>
</foo:document>

I want to evaluate "/foo:document/bar:element", which should return "MyBar".
I use the following code:

package test;

import java.util.Iterator;

import javax.xml.XMLConstants;
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.w3c.dom.Document;
import org.w3c.dom.Element;
import org.xml.sax.InputSource;

public class NamespaceTest
{
public static void main(String[] argv) throws Exception
{
String doc = " namespace.xml";
String xPath = "/foo:document/bar:element";

// Parse the doc independently to get the root Element
DocumentBuilderFactory fct = DocumentBuilderFactory.newInstance ();
DocumentBuilder builder = fct.newDocumentBuilder();
Document document = builder.parse("file:" + doc);
Element rootElement = document.getDocumentElement();

// Setup the namespace context
XPathFactory factory = XPathFactory.newInstance();
XPath xp = factory.newXPath();
NamespaceContext ctx = new MyNamespaceContext();
xp.setNamespaceContext(ctx);

// Create an InputSource of the file
InputSource is = new InputSource(doc);

// This works
String resultString1 = xp.evaluate(xPath,is);
// This doesn't
String resultString2 = xp.evaluate (xPath,rootElement);

System.out.println("RES1=" + resultString1);
System.out.println("RES2=" + resultString2);
}
}

class MyNamespaceContext implements NamespaceContext
{
public String getNamespaceURI(String prefix)
{
if (prefix.equals("foo"))
return "http://apache.org/foo";
else if ( prefix.equals("bar"))
return "http://apache.org/bar";
else
return XMLConstants.NULL_NS_URI;
}

public String getPrefix(String namespace)
{
if (namespace.equals("http://apache.org/foo"))
return "foo";
else if (namespace.equals(" http://apache.org/bar"))
return "bar";
else
return null;
}

public Iterator getPrefixes(String namespace)
{
return null;
}
}

When I execute this (against Xalan 2.7.0), resultString1 returns "MyBar"
correctly, resultString2 is set as empty string. Surely they should both
return the correct result? Interestingly, if I use the exact same code to
evaluate a namespace-free expression, both versions work fine.

Is this a bug, or am I doing something stupid with the rootElement I am
passing in?

Any and all assistance greatly appreciated,

Jason

Hi all, Apologies if this has been asked before but it is driving me mad
. I am happily able to evaluate non-namespaced XPath expressions using either an
InputSource or a document context element. I can evaluate namespaced
expressions using the InputSource, but it doesn't work if I evaluate a
namespaced expression passing an Element as a context node.
 Take the example file from <a href="http://xml.apache.org/xalan-j/xpath
_apis.html#namespacecontext" target="_blank" onclick="return top.js.OpenExtLink
(window,event,this)">http://xml.apache.org/xalan-j/xpath_apis.html
#namespacecontext
</a> <?xml version='1.0'?> 
  <foo:document xmlns:foo="<a href="http://apache.org/foo"
target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">http:/
/apache.org/foo</a>" xmlns:bar="<a href="http://apache.org/bar" target
="_blank" onclick="return top.js.OpenExtLink(window,event,this)">
http://apache.org/bar</a>">     <bar:element&gt
;MyBar</bar:element>
   </foo:document>   I want to evaluate "/foo
:document/bar:element", which should return "MyBar". I use the
following code: package test; import java.util.Iterator; 

import javax.xml.XMLConstants; 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.w3c.dom.Document; import org.w3c.dom.Element; import
org.xml.sax.InputSource; public class NamespaceTest {   
  public static void main(String[] argv) throws Exception   
  {         String doc = "
namespace.xml";         String xPath =
"/foo:document/bar:element";       
  // Parse the doc independently to get the root Element   
      DocumentBuilderFactory fct = DocumentBuilderFactory
.newInstance

();         DocumentBuilder builder = fct
.newDocumentBuilder();         Document
document = builder.parse("file:" + doc);      
   Element rootElement = document.getDocumentElement();  
       // Setup the namespace context
         XPathFactory factory = XPathFactory
.newInstance();         XPath xp = factory
.newXPath();         NamespaceContext ctx = new
MyNamespaceContext();         xp
.setNamespaceContext(ctx);         
        // Create an InputSource of the file
         InputSource is = new InputSource(doc)
;               
  // This works         String
resultString1 = xp.evaluate(xPath,is);        
// This doesn't         String
resultString2 = xp.evaluate

(xPath,rootElement);         System.out
.println("RES1=" + resultString1);       
  System.out.println("RES2=" + resultString2);   
  } } class MyNamespaceContext implements
NamespaceContext
 {     public String getNamespaceURI(String prefix) 
    {         if (prefix
.equals("foo"))         
    return "<a href="http://apache.org/foo" target="_blank"
onclick="return top.js.OpenExtLink(window,event,this)">
http://apache.org/foo</a>";        
else if (
prefix.equals("bar"))        
     return "<a href="http://apache.org/bar" target="
_blank" onclick="return top.js.OpenExtLink(window,event,this)">http://apache.org
/bar</a>";         else  
           return
XMLConstants.NULL_NS_URI;     }     
    public String getPrefix(String namespace)
     {         if
(namespace.equals("<a href="http://apache.org/foo" target="_blank" onclick=
"return top.js.OpenExtLink(window,event,this)">http://apache.org/foo</a>"))
             return
"foo";
         else if (namespace.equals("
<a href="http://apache.org/bar" target="_blank" onclick="return top.js
.OpenExtLink(window,event,this)">
http://apache.org/bar</a>"))        
     return "bar";     
    else         &nbsp
;   return null;     }    
public Iterator getPrefixes(String namespace)     {  
       return null;     }
 }  When I execute this (against Xalan 2.7.0),
resultString1 returns "MyBar" correctly, resultString2 is set as
empty string. Surely they should both return the correct result? Interestingly,
if I use the exact same code to evaluate a namespace-free expression, both
versions work fine.
 Is this a bug, or am I doing something stupid with the rootElement I am
passing in? Any and all assistance greatly appreciated, Jason