xsd:choice, pre-created elements, part 2 - writing a custom xpath function to remove empty elements

Thinking a little bit more on this issue, preferably on a sunday - and voila,
another solution came to my brain. Writing a custom XPATH function that removes
all the empty elements, from a given parent node.

Basically writing an BPEL XPATH function consists of 2 parts:

• a class that implements com.oracle.bpel.xml.xpath.IXPathFunction


• and is registered in xpath-functions.xml, located in $BPEL_HOME/domains/<domain name>/config

Ok, one step after the other

Step 1 - implementing the interface - the only method that is available and will be called is

public Object call(IXPathContext context,
                   List args) 
  throws XPathFunctionException;

Inside the class it's rather easy to retrieve parts, like the context, or any xpath queried elements as shown below

// retrieve the context ..
Map properties = 
  (Map) context.getVariableValue(null, null, 
        PathDefs.XPATH_FUNCTION_VARIABLE_DATA);

ICubeContext cubeContext = 
  (ICubeContext) properties.get(XPathDefs.CUBE_CONTEXT);

retrieving the xpath element from a query is not much deal too (in this case I expect one argument of type Element)

Element el = (CubeDOMElement) args.get(0) 

So the only thing left is implementing an algorithm to search the element (el) for empty nodes .. and remove them ..

Step 2 - registering the function with the BPEL Server
Next, open the xpath-functions.xml, located in $BPEL_HOME/domains/<domainname>/config, and add your new function.
I just copied one of the entries, changed the value of <function> to deleteEmptyElements, the <classname> to point to my new class, and gave the whole thing the right pprefix and namespace (as shown)

<property id="namespace-uri">
  <value>http://schemas.oracle.com/xpath/extension</value>
  <comment>Namespace URI for this function</comment>
</property>
<property id="namespace-prefix">
  <value>ora</value>
  <comment>Namespace prefix for this function</comment>
</property>

Using your new function in a process:
As written earlier, one argument of type element is expected, which can be easiliy retrieved throug using bpws:getVariableData function.

<copy>
  <from expression="ora:deleteEmptyElements(
                    bpws:getVariableData
                        ('outputVariable',
                         'payload',
                         '/client:UsingChoicesProcessResponse/
                          client:choiceTest'))"
  />
  <to variable="outputVariable" part="payload"
      query="/client:UsingChoicesProcessResponse/
              client:choiceTest"
  />
</copy>

still have questions? send your feedback on writing a custom xpath function here