XSLT

Since Camel 1.3

Only producer is supported

The XSLT component allows you to process a message using an XSLT template. This can be ideal when using Templating to generate response 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&…​

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

Configuring Options

Camel components are configured on two separate levels:

  • component level

  • endpoint level

Configuring Component Options

At the component level, you set general and shared configurations that are, then, inherited by the endpoints. It is the highest configuration level.

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.

You can configure components using:

  • the Component DSL.

  • in a configuration file (application.properties, *.yaml files, etc).

  • directly in the Java code.

Configuring Endpoint Options

You usually spend more time setting up endpoints because they have many options. These options help you customize what you want the endpoint to do. The options are also categorized into whether the endpoint is used as a consumer (from), as a producer (to), or both.

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

A good practice when configuring options is to use Property Placeholders.

Property placeholders provide a few benefits:

  • They help prevent using hardcoded urls, port numbers, sensitive information, and other settings.

  • They allow externalizing the configuration from the code.

  • They help the code to become more flexible and reusable.

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

Component Options

The XSLT component supports 8 options, which are listed below.

Name Description Default Type

allowTemplateFromHeader (producer)

Whether to allow to use resource template from header or not (default false). Enabling this allows to specify dynamic templates via message header. However this can be seen as a potential security vulnerability if the header is coming from a malicious user, so use this with care.

false

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

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

Endpoint Options

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 (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

Query Parameters (15 parameters)

Name Description Default Type

allowTemplateFromHeader (producer)

Whether to allow to use resource template from header or not (default false). Enabling this allows to specify dynamic templates via message header. However this can be seen as a potential security vulnerability if the header is coming from a malicious user, so use this with care.

false

boolean

contentCache (producer)

Cache for the resource content (the stylesheet file) when it is loaded on startup. 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 XsltConstants.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

lazyStartProducer (producer (advanced))

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

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

xsltMessageLogger (advanced)

A consumer to messages generated during XSLT transformations.

XsltMessageLogger

/ component headers: START

Message Headers

The XSLT component supports 3 message header(s), which is/are listed below:

Name Description Default Type

CamelXsltResourceUri (producer)

Constant: XSLT_RESOURCE_URI

A URI for the template resource to load and use instead of the endpoint configured.

String

CamelXsltStylesheet (producer)

Constant: XSLT_STYLESHEET

The template to use instead of the endpoint configured.

String

CamelXsltFileName (producer)

Constant: XSLT_FILE_NAME

The XSLT file name.

String

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");

Getting Usable Parameters into the XSLT

By default, all headers are added as parameters which are then available in the XSLT.
To make the parameters usable, 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 ...>

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>

Using xsl:include

Camel provides its own implementation of URIResolver. This allows Camel to load included files from the classpath.

For example, the included 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 included 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

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 an XSLT script, if necessary.

Dynamic stylesheets

To provide a dynamic stylesheet at runtime, you can either:

When using a header for dynamic stylesheet, then you can either refer to the stylesheet as a file or classpath with the header CamelXsltResourceUri, such as:

from("direct:transform")
    .setHeader("CamelXsltResourceUri", simple("file:styles/${header.region}.xsl"))
    .to("xslt:template.xsl?allowTemplateFromHeader=true");

Here we set the CamelXsltResourceUri header to refer to a stylesheet to be loaded from the file system, with a dynamic name that is computed from another header (region).

Notice how the allowTemplateFromHeader must be set to true on the XSLT endpoint to support dynamic templates.

You can also use the header CamelXsltStylesheet which instead should contain the content of the stylesheet to use, instead of referring to a file as the example from above.

You can set contentCache=false and refer to a non-existing template, such as "xslt:dummy.xsl?contentCache=false&allowTemplateFromHeader=true" as this will tell Camel to not load dummy.xsl on startup but to load the stylesheet on demand. And because you provide the stylesheet via headers, then it is fully dynamic.

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.

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>x.x.x</version>
  <!-- use the same version as your Camel core version -->
</dependency>

The component supports 9 options, which are listed below.

Name Description Default Type

camel.component.xslt.allow-template-from-header

Whether to allow to use resource template from header or not (default false). Enabling this allows to specify dynamic templates via message header. However this can be seen as a potential security vulnerability if the header is coming from a malicious user, so use this with care.

false

Boolean

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
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