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Chapter 141. XSLT

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
URI Description
xslt:com/acme/mytransform.xsl Refers to the file, com/acme/mytransform.xsl, on the classpath.
xslt:file:///foo/bar.xsl Refers to the file, /foo/bar.xsl.
xslt:http://acme.com/cheese/foo.xsl Refers to the remote HTTP resource.
From Camel 2.9 onwards the XSLT component is provided directly in the camel-core.

Options

Name Default Value Description
converter null Option to override default XmlConverter. 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. 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. 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 reloader the stylesheet file on each message processing. This is good for development.
allowStAX false Camel 2.8.3/2.9: Whether to allow using StAX as the javax.xml.transform.Source.
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.

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 forumulate 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 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.