Using parameters with XSLT in Mule

Recently I got into a situation where I had to put ‘metadata’ values (which were part of the Mule Message) into the XML result of an XSLT transformer. Let me explain the situation with an example. Imagine you have an ‘order’ xml that needs to be translated into an ‘invoice’ xml. Here is a simple ‘order.xsd’:

Here is the ‘invoice.xsd’:

The mapping for the transformation looks like this in MapForce:

Now the invoice number that is used in the invoice should be the MuleMessage correlationID…. (I know, weird situation, but it is only an example). The first thing that came to mind was to create a new transformer that would run after the XSLT transformer. This new transformer would add the element ‘invoicenr’ with the correlationID as value to the payload of the MuleMessage. But it can be done much easier! Here is the modified mapping that I created with MapForce:

In MapForce you can add extra input parameters for the XSL mapping as shown above. Now generate the XSLT and use that as basis for your Mule XSLT Transformer. In the Mule config you add the context-property to your XSL Transformer configuration to tell Mule with which value the parameter in the XSLT file should be filled:

<?xml version="1.0" encoding="UTF-8"?>
<mule xmlns="http://www.mulesource.org/schema/mule/core/2.2"
     xmlns:xm="http://www.mulesource.org/schema/mule/xml/2.2"
     ...
     xsi:schemaLocation="
      http://www.mulesource.org/schema/mule/xml/2.2 http://www.mulesource.org/schema/mule/xml/2.2/mule-xml.xsd
     ...
     ">
    <xm:xslt-transformer name="orderToInvoiceTransformer" xsl-file="xsl/order-to-invoice.xsl" outputEncoding="UTF-8">
        <xm:context-property key="invoiceNr" value="#[message:correlationId]"/>
    </ship:xslt-transformer>
    ...
</mule>

This makes it a very clean and powerful way to add metadata to your payload might you ever need this.