Extending WSO2 BPS 2.0.0 With Custom XPath Functions
by Milinda Lakmal
Latest release(version 2.0.0) of WSO2 BPS, includes a fix for supporting custom XPath functions based on Saxon. There was a class loading issue in the previous releases of WSO2 BPS, which breaks the custom XPath function support.
Now you can write your own custom XPath extension functions as described in Saxon’s extensibility documentation, deploy them on WSO2 BPS and use them in you process definitions.
To deploy your XPath extensions in WSO2 BPS, you need to copy them into the BPS_HOME/repository/components/lib directory.
When writing XPath extension functions, there are some special cases. For example, if you want to pass a BPEL variable(WSDL Message or XSD Element type) into your extension functions, in simplest way, you need to use net.sf.saxon.om.NodeInfo as the parameter type. According to Saxon documentations DOM Node as the input parameter also should work when you want to get a XML element as the input. but I couldn’t get it to work when I am doing tests. And if you need to access XPath processing context, you need to have XPathContext as the first parameter to your function. When you want to return XML elements from your extension functions, you can use return type as org.w3c.dom.Node.
When returning XML elements, please make sure to create them using DOM AI tried to create DOM from a string like following. But failed when evaluating XPath on the return value as well as converting that DOM to AXIOM OM when sending response back to the BPEL process caller at the integration layer.
Here is the final sample extension source.
And here is how you can use that extension inside BPEL process definition. In this sample, I am creating the response XML using this custom XPath function.
If you have any questions on custom XPath function in WSO2 BPS, please feel free to put comment on this post. You can use extension written following above guidelines in Apache ODE also. In Apache ODE case you need to copy extension JAR into Apache ODE web application’s lib directory or relevant place in your JBI based Apache ODE deployment.
