[CONF] Apache Camel: XSLT (page edited)

confluence Wed, 17 Jun 2009 08:53:34 -0700

Page Edited : CAMEL : XSLT

XSLT has been edited by Claus Ibsen (Jun 17, 2009).

Content:

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

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

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

Using XSLT endpoints

For example you could use something like

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

To use a 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

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.

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	New added in Camel 1.6 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	New added in Camel 1.6 Option to override default TransformerFactory. Will create a TransformerFactoryClass instance and set it to the coverter.

Notes on using XSTL and Java Versions

This is observations from Sameer, a Camel users, 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.