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XSLT

The xslt: component allows you to process a message using an XSLT template. This can be ideal when using Templating to generate respopnses for requests.

URI format

xslt:templateName[?options]

Where templateName is the classpath-local URI of the template to invoke; or the complete URL of the remote template. Refer to the Spring Documentation for more detail of the URI syntax

You can append query options to the URI in the following format, ?option=value&option=value&...

Here are some example URIs

{div:class=confluenceTableSmall}
|| URI || Description ||
| {code}xslt:com/acme/mytransform.xsl{code} | refers to the file com/acme/mytransform.xsl on the classpath |
| {code}xslt:file:///foo/bar.xsl{code} | refers to the file /foo/bar.xsl |
| {code}xslt:http://acme.com/cheese/foo.xsl{code} | refers to the remote http resource |
{div}

Maven users will need to add the following dependency to their pom.xml for this component when using Camel 2.8 or older:

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-spring</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

From Camel 2.9 onwards the XSLT component is provided directly in the camel-core.

Options

{div:class=confluenceTableSmall}
|| Name || Default Value || Description ||
| {{converter}} | {{null}} | Option to override default [XmlConverter|http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/converter/jaxp/XmlConverter.html]. Will lookup for the converter in the [Registry]. The provided converted must be of type org.apache.camel.converter.jaxp.XmlConverter. |
| {{transformerFactory}} | {{null}} | Option to override default [TransformerFactory|http://java.sun.com/j2se/1.5.0/docs/api/javax/xml/transform/TransformerFactory.html]. Will lookup for the transformerFactory in the [Registry]. The provided transformer factory must be of type javax.xml.transform.TransformerFactory. |
| {{transformerFactoryClass}} | {{null}} | Option to override default [TransformerFactory|http://java.sun.com/j2se/1.5.0/docs/api/javax/xml/transform/TransformerFactory.html]. Will create a TransformerFactoryClass instance and set it to the converter. |
| {{uriResolver}} | {{null}} | *Camel 2.3*: Allows you to use a custom {{javax.xml.transformation.URIResolver}}. Camel will by default use its own implementation {{org.apache.camel.builder.xml.XsltUriResolver}} which is capable of loading from classpath. |
| {{resultHandlerFactory}} | {{null}} | *Camel 2.3:* Allows you to use a custom {{org.apache.camel.builder.xml.ResultHandlerFactory}} which is capable of using custom {{org.apache.camel.builder.xml.ResultHandler}} types. |
| {{failOnNullBody}} | {{true}} | *Camel 2.3:* Whether or not to throw an exception if the input body is null. |
| {{deleteOutputFile}} | {{false}} | *Camel 2.6:* If you have {{output=file}} then this option dictates whether or not the output file should be deleted when the [Exchange] is done processing. For example suppose the output file is a temporary file, then it can be a good idea to delete it after use. |
| {{output}} | {{string}} | *Camel 2.3:* Option to specify which output type to use. Possible values are: {{string, bytes, DOM, file}}. The first three options are all in memory based, where as {{file}} is streamed directly to a {{java.io.File}}. For {{file}} you *must* specify the filename in the IN header with the key {{Exchange.XSLT_FILE_NAME}} which is also {{CamelXsltFileName}}. Also any paths leading to the filename must be created beforehand, otherwise an exception is thrown at runtime. |
| {{contentCache}} | {{true}} | *Camel 2.6:* Cache for the resource content (the stylesheet file) when it is loaded. If set to {{false}} Camel will reload the stylesheet file on each message processing. This is good for development. 
Note: from *Camel 2.9* a cached stylesheet can be forced to reload at runtime via JMX using the {{clearCachedStylesheet}} operation. |
| {{allowStAX}} | | *Camel 2.8.3/2.9:* Whether to allow using StAX as the {{javax.xml.transform.Source}}. The option is default {{false}} in Camel 2.11.3/2.12.2 or older. And default {{true}} in Camel 2.11.4/2.12.3 onwards. |
| {{transformerCacheSize}} | {{0}} | *Camel 2.9.3/2.10.1:*  The number of {{javax.xml.transform.Transformer}} object that are cached for reuse to avoid calls to {{Template.newTransformer()}}. |
| {{saxon}} | {{false}} | *Camel 2.11:* Whether to use Saxon as the {{transformerFactoryClass}}. If enabled then the class {{net.sf.saxon.TransformerFactoryImpl}}. You would need to add Saxon to the classpath. |
{div}

Using XSLT endpoints

For example you could use something like

from("activemq:My.Queue").
  to("xslt:com/acme/mytransform.xsl");

To use an XSLT template to formulate a response for a message for InOut message exchanges (where there is a JMSReplyTo header).

If you want to use InOnly and consume the message and send it to another destination you could use the following route:

from("activemq:My.Queue").
  to("xslt:com/acme/mytransform.xsl").
  to("activemq:Another.Queue");

Getting Parameters into the XSLT to work with

By default, all headers are added as parameters which are available in the XSLT.
To do this you will need to declare the parameter so it is then useable.

<setHeader headerName="myParam"><constant>42</constant></setHeader>
<to uri="xslt:MyTransform.xsl"/>

And the XSLT just needs to declare it at the top level for it to be available:

<xsl: ...... >

   <xsl:param name="myParam"/>
  
    <xsl:template ...>

Spring XML versions

To use the above examples in Spring XML you would use something like

  <camelContext xmlns="http://activemq.apache.org/camel/schema/spring">
    <route>
      <from uri="activemq:My.Queue"/>
      <to uri="xslt:org/apache/camel/spring/processor/example.xsl"/>
      <to uri="activemq:Another.Queue"/>
    </route>
  </camelContext>

There is a test case along with its Spring XML if you want a concrete example.

Using xsl:include

Camel 2.2 or older
If you use xsl:include in your XSL files then in Camel 2.2 or older it uses the default javax.xml.transform.URIResolver which means it can only lookup files from file system, and its does that relative from the JVM starting folder.

For example this include:

<xsl:include href="staff_template.xsl"/>

Will lookup the staff_tempkalte.xsl file from the starting folder where the application was started.

Camel 2.3 or newer
Now Camel provides its own implementation of URIResolver which allows Camel to load included files from the classpath and more intelligent than before.

For example this include:

<xsl:include href="staff_template.xsl"/>

Will now be located relative from the starting endpoint, which for example could be:

.to("xslt:org/apache/camel/component/xslt/staff_include_relative.xsl")

Which means Camel will locate the file in the classpath as org/apache/camel/component/xslt/staff_template.xsl.
This allows you to use xsl include and have xsl files located in the same folder such as we do in the example org/apache/camel/component/xslt.

You can use the following two prefixes classpath: or file: to instruct Camel to look either in classpath or file system. If you omit the prefix then Camel uses the prefix from the endpoint configuration. If that neither has one, then classpath is assumed.

You can also refer back in the paths such as

    <xsl:include href="../staff_other_template.xsl"/>

Which then will resolve the xsl file under org/apache/camel/component.

Using xsl:include and default prefix

When using xsl:include such as:

<xsl:include href="staff_template.xsl"/>

Then in Camel 2.10.3 and older, then Camel will use "classpath:" as the default prefix, and load the resource from the classpath. This works for most cases, but if you configure the starting resource to load from file,

.to("xslt:file:etc/xslt/staff_include_relative.xsl")

.. then you would have to prefix all your includes with "file:" as well.

<xsl:include href="file:staff_template.xsl"/>

From Camel 2.10.4 onwards we have made this easier as Camel will use the prefix from the endpoint configuration as the default prefix. So from Camel 2.10.4 onwards you can do:

<xsl:include href="staff_template.xsl"/>

Which will load the staff_template.xsl resource from the file system, as the endpoint was configured with "file:" as prefix.
You can still though explicit configure a prefix, and then mix and match. And have both file and classpath loading. But that would be unusual, as most people either use file or classpath based resources.

Dynamic stylesheets

Available as of Camel 2.9
Camel provides the CamelXsltResourceUri header which you can use to define a stylesheet to use instead of what is configured on the endpoint URI. This allows you to provide a dynamic stylesheet at runtime.

Notes on using XSLT and Java Versions

Here are some observations from Sameer, a Camel user, which he kindly shared with us:

In case anybody faces issues with the XSLT endpoint please review these points.

I was trying to use an xslt endpoint for a simple transformation from one xml to another using a simple xsl. The output xml kept appearing (after the xslt processor in the route) with outermost xml tag with no content within.

No explanations show up in the DEBUG logs. On the TRACE logs however I did find some error/warning indicating that the XMLConverter bean could no be initialized.

After a few hours of cranking my mind, I had to do the following to get it to work (thanks to some posts on the users forum that gave some clue):

1. Use the transformerFactory option in the route ("xslt:my-transformer.xsl?transformerFactory=tFactory") with the tFactory bean having bean defined in the spring context for class="org.apache.xalan.xsltc.trax.TransformerFactoryImpl".
2. Added the Xalan jar into my maven pom.

My guess is that the default xml parsing mechanism supplied within the JDK (I am using 1.6.0_03) does not work right in this context and does not throw up any error either. When I switched to Xalan this way it works. This is not a Camel issue, but might need a mention on the xslt component page.

Another note, jdk 1.6.0_03 ships with JAXB 2.0 while Camel needs 2.1. One workaround is to add the 2.1 jar to the jre/lib/endorsed directory for the jvm or as specified by the container.

Hope this post saves newbie Camel riders some time.