XSLT

Since Camel 1.3

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]

The URI format contains templateName, which can be one of the following:

  • the classpath-local URI of the template to invoke

  • the complete URL of the remote template.

You can append query options to the URI in the following format:

?option=value&option=value&…​

Refer to the Spring Documentation for more detail of the URI syntax.

Table 1. 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

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

<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

The XSLT component supports 9 options, which are listed below.

Name Description Default Type

xmlConverter (advanced)

To use a custom implementation of org.apache.camel.converter.jaxp.XmlConverter

XmlConverter

uriResolverFactory (advanced)

To use a custom UriResolver which depends on a dynamic endpoint resource URI. Should not be used together with the option 'uriResolver'.

XsltUriResolverFactory

uriResolver (advanced)

To use a custom UriResolver. Should not be used together with the option 'uriResolverFactory'.

URIResolver

contentCache (producer)

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. A cached stylesheet can be forced to reload at runtime via JMX using the clearCachedStylesheet operation.

true

boolean

saxon (producer)

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.

false

boolean

saxonExtensionFunctions (advanced)

Allows you to use a custom net.sf.saxon.lib.ExtensionFunctionDefinition. You would need to add camel-saxon to the classpath. The function is looked up in the registry, where you can comma to separate multiple values to lookup.

String

saxonConfiguration (advanced)

To use a custom Saxon configuration

Object

saxonConfiguration Properties (advanced)

To set custom Saxon configuration properties

Map

resolveProperty Placeholders (advanced)

Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders.

true

boolean

The XSLT endpoint is configured using URI syntax:

xslt:resourceUri

with the following path and query parameters:

Path Parameters (1 parameters):

Name Description Default Type

resourceUri

Required Path to the template. The following is supported by the default URIResolver. You can prefix with: classpath, file, http, ref, or bean. classpath, file and http loads the resource using these protocols (classpath is default). ref will lookup the resource in the registry. bean will call a method on a bean to be used as the resource. For bean you can specify the method name after dot, eg bean:myBean.myMethod

String

Query Parameters (17 parameters):

Name Description Default Type

allowStAX (producer)

Whether to allow using StAX as the javax.xml.transform.Source.

true

boolean

contentCache (producer)

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. A cached stylesheet can be forced to reload at runtime via JMX using the clearCachedStylesheet operation.

true

boolean

deleteOutputFile (producer)

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.

false

boolean

failOnNullBody (producer)

Whether or not to throw an exception if the input body is null.

true

boolean

output (producer)

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.

string

XsltOutput

saxon (producer)

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.

false

boolean

transformerCacheSize (producer)

The number of javax.xml.transform.Transformer object that are cached for reuse to avoid calls to Template.newTransformer().

0

int

converter (advanced)

Deprecated To use a custom implementation of org.apache.camel.converter.jaxp.XmlConverter

XmlConverter

entityResolver (advanced)

To use a custom org.xml.sax.EntityResolver with javax.xml.transform.sax.SAXSource.

EntityResolver

errorListener (advanced)

Allows to configure to use a custom javax.xml.transform.ErrorListener. Beware when doing this then the default error listener which captures any errors or fatal errors and store information on the Exchange as properties is not in use. So only use this option for special use-cases.

ErrorListener

resultHandlerFactory (advanced)

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.

ResultHandlerFactory

saxonConfiguration (advanced)

To use a custom Saxon configuration

Object

saxonExtensionFunctions (advanced)

Allows you to use a custom net.sf.saxon.lib.ExtensionFunctionDefinition. You would need to add camel-saxon to the classpath. The function is looked up in the registry, where you can comma to separate multiple values to lookup.

String

synchronous (advanced)

Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported).

false

boolean

transformerFactory (advanced)

To use a custom XSLT transformer factory

TransformerFactory

transformerFactoryClass (advanced)

To use a custom XSLT transformer factory, specified as a FQN class name

String

uriResolver (advanced)

To use a custom javax.xml.transform.URIResolver

URIResolver

Using XSLT endpoints

The following format is an expample of using an XSLT template to formulate a response for a message for InOut message exchanges (where there is a JMSReplyTo header)

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

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 Useable Parameters into the XSLT

By default, all headers are added as parameters which are then available in the XSLT.
To make the parameters useable, you will need to declare them.

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

The parameter also needs to be declared in the top level of the XSLT 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 the following code:

  <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>

To see an example, look at the test case along with its Spring XML.

Using xsl:include

Camel 2.2 or older
If you use xsl:include in your XSL files in Camel 2.2 or older, the default javax.xml.transform.URIResolver is used. Files will be resolved relative to the JVM starting folder.

For example the following include statement will look up the staff_template.xsl file starting from the folder where the application was started.

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

Camel 2.3 or newer
For Camel 2.3 or newer, Camel provides its own implementation of URIResolver. This allows Camel to load included files from the classpath.

For example the include file in the following code will be located relative to the starting endpoint.

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

This means that Camel will locate the file in the classpath as org/apache/camel/component/xslt/staff_template.xsl

You can use classpath: or file: to instruct Camel to look either in the classpath or file system. If you omit the prefix then Camel uses the prefix from the endpoint configuration. If no prefix is specified in the endpoint configuration, the default is classpath:.

You can also refer backwards in the include paths. In the following example, the xsl file will be resolved under org/apache/camel/component.

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

Using xsl:include and default prefix

In Camel 2.10.3 and older, classpath: is used as the default prefix.
If you configure the starting resource to load using file: then all subsequent incudes will have to be prefixed with file:.

From Camel 2.10.4, Camel will use the prefix from the endpoint configuration as the default prefix.

You can explicitly specify file: or classpath: loading. The two loading types can be mixed in a XSLT script, if necessary.

Using Saxon extension functions

Since Saxon 9.2, writing extension functions has been supplemented by a new mechanism, referred to as http://www.saxonica.com/html/documentation/extensibility/integratedfunctions[integrated extension functions] you can now easily use camel as shown in the below example:

SimpleRegistry registry = new SimpleRegistry();
registry.put("function1", new MyExtensionFunction1());
registry.put("function2", new MyExtensionFunction2());

CamelContext context = new DefaultCamelContext(registry);
context.addRoutes(new RouteBuilder() {
    @Override
    public void configure() throws Exception {
        from("direct:start")
            .to("xslt:org/apache/camel/component/xslt/extensions/extensions.xslt?saxonExtensionFunctions=#function1,#function2");
    }
});

With Spring XML:

<bean id="function1" class="org.apache.camel.component.xslt.extensions.MyExtensionFunction1"/>
<bean id="function2" class="org.apache.camel.component.xslt.extensions.MyExtensionFunction2"/>

<camelContext xmlns="http://camel.apache.org/schema/spring">
  <route>
    <from uri="direct:extensions"/>
    <to uri="xslt:org/apache/camel/component/xslt/extensions/extensions.xslt?saxonExtensionFunctions=#function1,#function2"/>
  </route>
</camelContext>

Dynamic stylesheets

To provide a dynamic stylesheet at runtime you can define a dynamic URI. See How to use a dynamic URI in to() for more information.

Since Camel 2.9 (removed in 2.11.4, 2.12.3 and 2.13.0

Camel provides the CamelXsltResourceUri header which you can use to define an alternative stylesheet to that configured on the endpoint URI. This allows you to provide a dynamic stylesheet at runtime.

Accessing warnings, errors and fatalErrors from XSLT ErrorListener

Since Camel 2.14

From Camel 2.14, any warning/error or fatalError is stored on the current Exchange as a property with the keys Exchange.XSLT_ERROR, Exchange.XSLT_FATAL_ERROR, or Exchange.XSLT_WARNING which allows end users to get hold of any errors happening during transformation.

For example in the stylesheet below, we want to terminate if a staff has an empty dob field. And to include a custom error message using xsl:message.

<xsl:template match="/">
  <html>
    <body>
      <xsl:for-each select="staff/programmer">
        <p>Name: <xsl:value-of select="name"/><br />
          <xsl:if test="dob=''">
            <xsl:message terminate="yes">Error: DOB is an empty string!</xsl:message>
          </xsl:if>
        </p>
      </xsl:for-each>
    </body>
  </html>
</xsl:template>

The exception is stored on the Exchange as a warning with the key Exchange.XSLT_WARNING.

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.

See Also

  • Configuring Camel

  • Component

  • Endpoint

  • Getting Started

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