Chapter 54. XSLT

54.1. 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&…

Table 54.1. 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

54.2. Configuring Options

Camel components are configured on two separate levels:

component level
endpoint level

54.2.1. Configuring Component Options

The component level is the highest level which holds general and common configurations that are inherited by the endpoints. For example a component may have security settings, credentials for authentication, urls for network connection and so forth.

Some components only have a few options, and others may have many. Because components typically have pre configured defaults that are commonly used, then you may often only need to configure a few options on a component; or none at all.

Configuring components can be done with the Component DSL, in a configuration file (application.properties|yaml), or directly with Java code.

54.2.2. Configuring Endpoint Options

Where you find yourself configuring the most is on endpoints, as endpoints often have many options, which allows you to configure what you need the endpoint to do. The options are also categorized into whether the endpoint is used as consumer (from) or as a producer (to), or used for both.

Configuring endpoints is most often done directly in the endpoint URI as path and query parameters. You can also use the Endpoint DSL as a type safe way of configuring endpoints.

A good practice when configuring options is to use Property Placeholders, which allows to not hardcode urls, port numbers, sensitive information, and other settings. In other words placeholders allows to externalize the configuration from your code, and gives more flexibility and reuse.

The following two sections lists all the options, firstly for the component followed by the endpoint.

54.3. Component Options

The XSLT component supports 7 options, which are listed below.

Name	Description	Default	Type
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
lazyStartProducer (producer)	Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.	false	boolean
autowiredEnabled (advanced)	Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc.	true	boolean
transformerFactoryClass (advanced)	To use a custom XSLT transformer factory, specified as a FQN class name.		String
transformerFactoryConfigurationStrategy (advanced)	A configuration strategy to apply on freshly created instances of TransformerFactory.		TransformerFactoryConfigurationStrategy
uriResolver (advanced)	To use a custom UriResolver. Should not be used together with the option 'uriResolverFactory'.		URIResolver
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

54.4. Endpoint Options

The XSLT endpoint is configured using URI syntax:

xslt:resourceUri

with the following path and query parameters:

54.4.1. Path Parameters (1 parameters)

Name	Description	Default	Type
resourceUri (producer)	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

54.4.2. Query Parameters (13 parameters)

Name	Description	Default	Type
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
lazyStartProducer (producer)	Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.	false	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. Enum values: string bytes DOM file	string	XsltOutput
transformerCacheSize (producer)	The number of javax.xml.transform.Transformer object that are cached for reuse to avoid calls to Template.newTransformer().	0	int
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
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
transformerFactoryConfigurationStrategy (advanced)	A configuration strategy to apply on freshly created instances of TransformerFactory.		TransformerFactoryConfigurationStrategy
uriResolver (advanced)	To use a custom javax.xml.transform.URIResolver.		URIResolver

54.5. Using XSLT endpoints

The following format is an example 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");

54.6. 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 name="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 ...>

54.7. 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>

54.8. Using xsl:include

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"/>

54.9. Using xsl:include and default prefix

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.

54.10. 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.

54.11. Accessing warnings, errors and fatalErrors from XSLT ErrorListener

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.

54.12. Spring Boot Auto-Configuration

When using xslt with Spring Boot make sure to use the following Maven dependency to have support for auto configuration:

<dependency>
  <groupId>org.apache.camel.springboot</groupId>
  <artifactId>camel-xslt-starter</artifactId>
  <version>3.14.5.redhat-00032</version>
  <!-- use the same version as your Camel core version -->
</dependency>

The component supports 8 options, which are listed below.

Name	Description	Default	Type
camel.component.xslt.autowired-enabled	Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc.	true	Boolean
camel.component.xslt.content-cache	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
camel.component.xslt.enabled	Whether to enable auto configuration of the xslt component. This is enabled by default.		Boolean
camel.component.xslt.lazy-start-producer	Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.	false	Boolean
camel.component.xslt.transformer-factory-class	To use a custom XSLT transformer factory, specified as a FQN class name.		String
camel.component.xslt.transformer-factory-configuration-strategy	A configuration strategy to apply on freshly created instances of TransformerFactory. The option is a org.apache.camel.component.xslt.TransformerFactoryConfigurationStrategy type.		TransformerFactoryConfigurationStrategy
camel.component.xslt.uri-resolver	To use a custom UriResolver. Should not be used together with the option 'uriResolverFactory'. The option is a javax.xml.transform.URIResolver type.		URIResolver
camel.component.xslt.uri-resolver-factory	To use a custom UriResolver which depends on a dynamic endpoint resource URI. Should not be used together with the option 'uriResolver'. The option is a org.apache.camel.component.xslt.XsltUriResolverFactory type.		XsltUriResolverFactory