Hi,
I've created a few classes using and mainly inspired by Xalan's XPath
implementation, adding a new functionality to the low-level XPath API,
which I think might be of some interest for the community. Thus I would
be happy to share the code if
- Given the description below, is this functionality eligible for a
contribution?
- If yes, how can I submit the source code?
The functionality is similar to the org.apache.xpath.CachedXPathAPI
class, providing equivalent cache capability, but allowing to
dynamically extend the namespace context in order to perform XPath
queries using EXSLT-implemented functions as well as custom functions
out of an XSLT transformation, but still in a "context-aware" mode. By
default, when using the Xalan low-level XPath API, custom functions
having an org.apache.xalan.extensions.ExpressionContext as their first
argument will always get a null reference of it when called. For
example, EXSLT's dyn:evaluate will throw an exception if used in the
low-level API. Of course this function has no reasonable utility in this
situation, but I wanted to implement a "sort" function working in a
similar way to the xsl:sort element, allowing to compare nodes in a node
set according to an XPath sort expression:
public static NodeList sort(ExpressionContext context, NodeList
nodelist, String sortExpression, String dataType, String order) throws
SAXNotSupportedException;
The implementation requires to manipulate the given context in order to
perform the given sort expression on each node of the given nodelist,
and thus cannot be used with the default low-level XPath API. With this
functionality, one could use a ContextualXPathAPI class, providing the
same methods as CachedXPathAPI (as well as convenience methods for
retrieving the 5 possible data types), but allowing to extend the
namespace context in a static way:
public static void addNamespacePrefixMapping(String prefix, String
namespaceURI);
public static void removeNamespacePrefixMapping(String prefix);
Here's an usage example, assuming there's a mypackage.XPathFunctions
class defining a sort method as stated above:
...
Node contextNode = ... // obtain a node reference
// extensions defined in
org.apache.xalan.extensions.ExtensionNamespaceContext are mapped by default
ContextualXPathAPI.addNamespacePrefixMapping("xpf",
"xalan://mypackage.XPathFunctions");
ContextualXPathAPI xPathAPI = new ContextualXPathAPI();
NodeList nodeList = xPathAPI.getNodeSet(contextNode, "xpf:sort(//*,
'name()', 'text', 'ascending')");
// one can use the same xPathAPI instance as long as the requested
context node doesn't change
...
If I missed a similar functionality while exploring Xalan distribution,
could someone show me the relevant classes, or simply ignore this
message, with my apologies.
--
Jerome Droz
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