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XSLT Transformations with the XML Module

The <xml-module:xslt-transform> element can take an input XML document and transform it using an XSL style sheet.

Although MuleSoft supports the XSLT standard, DataWeave is the recommended tool for extracting and transforming XML documents.

This is an example XML input document:

<?xml version="1.0" encoding="UTF-8"?>
<cities>
    <city name="milan"  country="italy"   pop="5"/>
    <city name="paris"  country="france"  pop="7"/>
    <city name="munich" country="germany" pop="4"/>
    <city name="lyon"   country="france"  pop="2"/>
    <city name="venice" country="italy"   pop="1"/>
</cities>

You can transform the XML input document like this:

<xml-module:xslt-transform>
    <xml-module:xslt><![CDATA[
    <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">

        <xsl:template match="/">
            <table>
            <tr>
                <th>Country</th>
                <th>City List</th>
                <th>Population</th>
            </tr>
            <xsl:for-each-group select="cities/city" group-by="@country">
                <tr>
                    <td>
                        <xsl:value-of select="@country"/>
                    </td>
                    <td>
                        <xsl:value-of select="current-group()/@name" separator=", "/>
                    </td>
                    <td>
                        <xsl:value-of select="sum(current-group()/@pop)"/>
                    </td>
                </tr>
            </xsl:for-each-group>
            </table>
        </xsl:template>
    </xsl:stylesheet>
]]></xml-module:xslt>
</xml-module:xslt-transform>

This script outputs the following document:

<table>
    <tr>
        <th>Country</th>
        <th>City List</th>
        <th>Population</th>
    </tr>
    <tr>
        <td>italy</td>
        <td>milan, venice</td>
        <td>6</td>
    </tr>
    <tr>
        <td>france</td>
        <td>paris, lyon</td>
        <td>9</td>
    </tr>
    <tr>
        <td>germany</td>
        <td>munich</td>
        <td>4</td>
    </tr>
</table>

Although this operation looks for the input document at the message payload level by default, you can supply your own input. For example, imagine that the cities are a JSON array inside the payload. You could then first transform the JSON to XML, and then run the XSL transformation:

<xml-module:xslt-transform>
    <xml-module:content><![CDATA[
                %dw 2.0
                input payload application/json encoding='UTF-8'
                output application/xml encoding='UTF-8'
                ---
                payload.cities
    ]]></xml-module:content>
    <xml-module:xslt><![CDATA[
        // THE XSLT
    ]]></xml-module:xslt>
</xml-module:xslt-transform>

Externalizing the XSL Style Sheet to a Separate File

To avoid embedding the XSLT script in your Mule app, you can pass it to the module through a file, for example:

<xml-module:xslt-transform>
    <xml-module:xslt>${file::xslt/cities.xslt}</xml-module:xslt>
</xml-module:xslt-transform>

In a more complex use case, the script you use might depend on some external condition. For example, imagine a multi-tenant integration in which the transformation to use depends on a userId:

<flow name="multitenantExample">
    <http:listener path="transform" allowedMethods="POST" config-ref="httpListener" /> // 1
    <file:read path="#['xslt/$(attributes.queryParam.userId).xslt']" target="xslt" />
    <xml-module:xslt-transform>
        <xml-module:xslt>#[vars.xslt]</xml-module:xslt>
    </xml-module:xslt-transform>
</flow>
  1. The example flow is triggered through an HTTP request.

  2. The example is based on the userId value being provided as a query parameter and the File Connector being used to read the file that contains the correct XSL and store it in a variable.

  3. The example then executes a transformation using an expression to point to the XSL sheet obtained through the Read operation.

The HTTP and File Connectors are used as examples and are not required to perform similar use cases.

Using Context Properties

The XML module, like the XSL language, provides context properties that can pass parameters to the transformation. In this example, the <xml-module:context-properties/> element contains a DataWeave expression that constructs an arguments map.

<xml-module:xslt-transform>
    <xml-module:xslt><![CDATA[
    <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="3.0">
        <xsl:output method="xml"/>

        <xsl:param name="vtn" /> (1)
        <xsl:template match="/parameter">
            <param><xsl:value-of select="$vtn"/></param> (2)
        </xsl:template>
    </xsl:stylesheet>
]]></xml-module:xslt>
    <xml-module:context-properties>#[{'vtn' : 'some value'}] (3)
    </xml-module:context-properties>
</xml-module:xslt-transform>
  1. The XSL style sheet declares a param called vtn.

  2. The style sheet references the assigned value of the param using the $ prefix.

  3. The example uses the context-properties parameter to pass in the values.

Output MIME Type

The most common use case for XSLT is to output a new XML document. However, XSLT can produce documents in other formats, such as JSON, CSV, or a text or number value, which means that the produced value does not have any specific MIME type assigned. You should specify a MIME type using the outputMimeType parameter.

See Also

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