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Chapter 144. XSLT
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.
144.1. Dependencies
When using xslt with Red Hat build of Camel 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> </dependency>
144.2. 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&…
| 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 |
144.3. Configuring Options
Camel components are configured on two levels:
- Component level
- Endpoint level
144.3.1. Component Level Options
The component level is the highest level. The configurations you define at this level are inherited by all the endpoints. For example, a component can have security settings, credentials for authentication, urls for network connection, and so on.
Since components typically have pre-configured defaults for the most common cases, you may need to only configure a few component options, or maybe none at all.
You can configure components with Component DSL in a configuration file (application.properties|yaml), or directly with Java code.
144.3.2. Endpoint Level Options
At the Endpoint level you have many options, which you can use to configure what you want the endpoint to do. The options are categorized according to whether the endpoint is used as a consumer (from) or as a producer (to) or used for both.
You can configure endpoints directly in the endpoint URI as path and query parameters. You can also use Endpoint DSL and DataFormat DSL as type safe ways of configuring endpoints and data formats in Java.
When configuring options, use Property Placeholders for urls, port numbers, sensitive information, and other settings.
Placeholders allows you to externalize the configuration from your code, giving you more flexible and reusable code.
144.4. 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 |
144.5. Endpoint Options
The XSLT endpoint is configured using URI syntax:
xslt:resourceUri
with the following path and query parameters:
144.5.1. 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 |
144.5.2. 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 | 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 |
144.6. 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");144.7. 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 ...>144.8. 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>144.9. 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"/>
144.10. 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.
144.11. 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.
144.12. 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.
144.13. Spring Boot Auto-Configuration
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 |
