This version must be installed on Petals ESB 5.0.2+ Features The XSLT Service-Engine allows to transform Petals messages using XSL style sheets. Each configuration of this component embeds an XSL style sheet. When such a configuration (i.e. service, i.e. service-unit) is called, it transforms the received message into another one. The XML payload of the input message is transformed using the XSL style sheet. The resulting XML document is then returned in the response, either as the payload, or as an attachment. This component only acts as service provider, not as a service consumer. In fact, it provides a transformation service. Additional information about XSLT can be found at http://www.w3.org/TR/xslt. XSLT Component overview Recommended usage The XSLT component should be used when chaining calls to services whose output and input do not match. It can also be used to expose XSL transformations as a service, provided that the content to transform is passed in the message payload, and not as attachment. Taking an example Let's take the example of two "white pages" services. These services aims at helping in finding where a person lives (or how to contact this person). First, you want to call the operation lookup of a service "White Pages". This operation takes the first name and the family name of a person, and returns a list of phone numbers. Each phone number is given as a string. Its prototype looks like lookup( String firstName, String familyName ) --> String[] phoneNumbers Do not forget this prototype would be in fact described in the WSDL interface of the service (under an XML shape). Then, you want to call a service that finds a geographical area (e.g. a city) from a phone prefix. It is the operation resolve from a service "PrefixToAreaLocalizer". From a phone prefix, it returns a geographical area. Its prototype looks like resolve( int phonePrefix ) --> String areaName Once again, this prototype is described in the WSDL interface of this second service. To chain these calls, you have to transform the output of the operation lookup to match the input of the operation resolve. Indeed, you cannot directly execute resolve( lookup( "Pierre", "Paul")); What you will do in your XSL style sheet is extracting the phone prefix from a phone number. The list go-through will most likely not be made in the XSLT transformation. There is no more simple way to make the transformation. In Petals, as well as in most of SOA-related technologies, messages are XML messages. And for every service, the operations, with their in and out parameters, are described in their WSDL interface. So, the output message of the resolve operation is an XML (SOAP) message, and the input message of resolve operation is an XML message too. These XML messages must match the WSDL descriptions of these services. Obviously, this example is extremely simple. But the usage remains the same, even with complex XML structures. XSLT and chaining services Following our previous example, it appears that chaining and transforming service calls implies using a chaining service (some could say an orchestration service). This chaining service would do the following calls: Message from the chaining service to a first service. Response from the first service to the chaining service (we assume the first service works in InOut message exchange pattern). Message from the chaining service to the XSLT service. Response from the XSLT service to the chaining service (the MEP is InOut, always). Message from the chaining service to a second service. The transformed message is sent to it. Optional response, depending on the MEP for the second service. This chaining service can be implemented by a POJO (an home made Java Class) or an Enterprise Integration Pattern (EIP). It could also be implemented by a BPEL process, but in fact, that would not be a great idea. BPEL supports the extraction of data from XML messages during the orchestration. When you have a BPEL process, you do not need XSLT. You can use XPath expressions and functions directly in the BPEL. Besides, working with BPEL would require the XSLT configuration to have a WSDL interface while they do not always have one. Limitations and warnings The transformed content is always the payload from the input message. Do not mistake XSLT services for interceptors. A XSL transformation service cannot transform messages addressed to another service. Neither to transform attachments, nor to intercept messages on the fly. An orchestration service is required to make the link. Interceptors would better fit this kind of use case. To work with XSL style sheets of more than 1000 lines, you have to use another engine than the default one shipped with Java (Xalan 2.6.0 for Java 6 for Petals <5 and Xalan 2.7.0 for Java 7 for Petals >5). This is due to a bug of Xalan of versions previous than 2.7.1. To bypass it, you have to use a newer version of Xalan (2.7.1 +) or another XSLT engine using a Shared-Library. Note that for version 2.5 up to 2.7, Saxon is the default engine, so the problem does not arise.

Table of contents 1 Features 2 Recommended usage 2.1 Taking an example 2.2 XSLT and chaining services 2.3 Limitations and warnings 3 Creating a XSL Transformation service (Provides modes) 3.1 The "transform" operation 3.2 The "transformToMtomAttachment" operation 3.3 XSL parameters 3.4 XSLT transformer processor 3.5 XSLT efficiency 3.6 WSDL definitions 3.7 JBI descriptor 3.7.1.1 Interceptor 3.8 Service-Unit content 4 Configuring the component 4.1.1.1 Interceptor 5 Monitoring the component 5.1 Using metrics 5.1.1 Common metrics 5.1.2 Dedicated metrics 5.2 Receiving alerts 5.2.1 Common alerts 5.2.2 Dedicated alerts Contributors No contributors found for: authors on selected page(s)

Creating a XSL Transformation service (Provides modes)

Each XSLT service runs on the Petals XSLT component.
The Petals XSLT component has native operations to invoke. These operations are inherited by the XSLT services.
A XSLT service cannot add additional operations. It only has the ones of the XSLT component.

The version 2.5 of the Petals XSLT component exposes two operations.

• transform: the received message is transformed with the XSL style sheet. The transformation result is returned as the response payload.
• transformToMtomAttachment: the received message is transformed with the XSL style sheet. The transformation result is attached to the response in MTOM mode.

The "transform" operation

The fully qualified name of this operation is:

• Name space URI: any URI, provided it is not null (e.g. *http://petals.ow2.org/components/xslt/version-2*)
• Local part: transform

This operation only supports the InOut message exchange pattern (MEP).
When invoking this operation, you must call it using its fully qualified name.
It must also be the operation name in the WSDL of any XSLT service.

Here is the execution flow for this operation:

1. The received message is transformed with the XSL style sheet.
2. The transformation result is returned as the response payload.

The result of the transformation depends on the XSL style sheet.

If an error occurs during the transformation, then a fault is raised.

<?xml version="1.0" encoding="UTF-8"?>
<xsltFault xmlns="the name space of the invoked operation">
    <message>An error message</message>
    <details>A stack trace (optional)</details>
</xsltFault>

Don't forget to enable the attachment forward (forward-attachments) when transforming an incoming request containing MTOM reference.

The "transformToMtomAttachment" operation

The fully qualified name of this operation is:

• Name space URI: any URI, provided it is not null (e.g. *http://petals.ow2.org/components/xslt/version-2*)
• Local part: transformToMtomAttachment

This operation only supports the InOut message exchange pattern (MEP).
When invoking this operation, you must call it using its fully qualified name.
This operation cannot be described in a WSDL, because of the result it returns.

Here is the execution flow for this operation:

1. The received message is transformed with the XSL style sheet.
2. The transformation result is attached to the response in MTOM mode.

The attachment is not sent in MTOM mode.
The result of the transformation has always the same shape.

<<attachedTransformResponse xmlns="..." xmlns:xop="http://www.w3.org/2004/08/xop/include">
    <fileContent>
        <xop:include href="cid:attachmentName" />
    </fileContent>
<<attachedTransformResponse>

... where attachmentName is the name of the attachment (as specified in the service-unit, or a default value otherwise).

If an error occurs during the transformation, then a fault is raised.

<?xml version="1.0" encoding="UTF-8"?>
<xsltFault xmlns="the name space of the invoked operation">
    <message>An error message</message>
    <details>A stack trace (optional)</details>
</xsltFault>

XSL parameters

XSL style sheets supports the definition of parameters.
These parameters can be passed dynamically when executing it.

You can find additional information about it on these web sites:

• http://www.w3schools.com/XSL/el_param.asp
• http://projects.ischool.washington.edu/tabrooks/545/ContentManagement/PassingParameters.htm
• http://www.xml.com/pub/a/2001/02/07/trxml9.html

The Petals XSLT component allows you to set XSL parameters in two different ways:

• The first one is a static definition in the jbi.xml.
  • It allows you to reuse a same XSL style sheet in several services.
  • Take a look at the jbi.xml parameters for more information.

• The second way is by setting them at runtime, in the message properties.
  • Please, understand that this is not the message payload that defines the parameter values.
  • It is the properties of the incoming Petals service (called an exchange). For more details, see Exchange#setInMessageProperty( String, Object ).

Static parameter values may be overriden by dynamic ones.
But only if the static values were defines as overridable.
Trying to override a parameter value that is not overridable will result in a fault.

Remember, XSL parameters are declared with a param element in the XSL style-sheet. A XSL parameter can be global (declared as a root element) or local (declared inside a template). The value of a XSL parameter can be retrieved with $parameter_name or {$parameter_name}, depending on the parameter usage.

XSLT transformer processor

The Petals XSLT component enables you to choose the XSLT processor.

By default, Xalan 2.7.0 (shipped with Java 7) is used as the default XSLT engine. It is possible to select another XSLT processor for a specific SU than the default one by:

• installing a shared library containing the XSLT processor to use,
• setting this shared library into the Petals XSLT component,
• AND the XSL transformer factory classname parameter in the jbi.xml of the SU.

To set the shared library to use into the Petals XSLT component, use the Petals maven plugin.

XSLT efficiency

A pool of XSL transformers is created for each SU at its start in order to obtain better performance. Two parameters enable you to set the number of XSL transformers to create at the start of the SU and the maximum number of transformers to instantiate. If all the XSL transformers are used (because of receiving a lot of requests concurrently on the service), the request blocks until a transformer is released.

WSDL definitions

Configurations (service-units) for the XSLT component do not have, in general, a WSDL definition.
However, it is possible to define one which describes the transform and "transformToMtomAttachment" operations.

The input and output messages for the transform operation are related to the XSL style sheet.
In fact, the input message should be the output message of the previous chained service (the one whose output must be transformed).
And the output message should be the input message of the next chained service.

The input message for the transformToMtomAttachment operation is related to the XSL style sheet.
In fact, the input message should be the output message of the previous chained service (the one whose output must be transformed). The WSDL message should reference a XML element of the same type than the input message of the transform operation.
And the output message should describe the MTOM structure that was documented above. In this structure, fileContent is a base64Binary element and the xop:include element does not appear.

As said at the beginning of this section, WSDL are not mandatory though. Typically, integration use cases do not require one. But not having one is bad practice in SOA.
Your XSLT service is then not reusable, and no one else will ever use it unless you give him the XSL style sheet to determine the expected input and output.

Beginning by creating a WSDL, and then continuing by the XSL style sheet appears as the best practice to have.

JBI descriptor

The Service-Unit descriptor file ( jbi.xml ) looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<?xml version="1.0" encoding="UTF-8"?>
<!--
	JBI descriptor for the Petals' "petals-se-xslt" component (XSLT).
	Originally created for the version 2.5 of the component.
 -->
<jbi:jbi version="1.0"
	xmlns:generatedNs="http://petals.ow2.org/components/xslt/version-2"
	xmlns:jbi="http://java.sun.com/xml/ns/jbi"
	xmlns:petalsCDK="http://petals.ow2.org/components/extensions/version-5"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:xslt="http://petals.ow2.org/components/xslt/version-2">

	<!-- Import a Service into Petals or Expose a Petals Service => use a BC. -->
	<jbi:services binding-component="false">

		<!-- Import a Service into Petals => provides a Service. -->
		<jbi:provides
			interface-name="generatedNs:XsltInterface"
			service-name="generatedNs:Test"
			endpoint-name="TestEndpoint">

			<!-- CDK specific elements -->
			<petalsCDK:timeout>30000</petalsCDK:timeout>
			<petalsCDK:validate-wsdl>true</petalsCDK:validate-wsdl>
			<petalsCDK:forward-security-subject>false</petalsCDK:forward-security-subject>
			<petalsCDK:forward-message-properties>false</petalsCDK:forward-message-properties>
			<petalsCDK:forward-attachments>false</petalsCDK:forward-attachments>
			<petalsCDK:wsdl>XsltService.wsdl</petalsCDK:wsdl>

			<!-- Component specific elements -->
			<xslt:stylesheet>transformation.xsl</xslt:stylesheet>

			<!-- XSL parameters -->
			<generatedNs:xsl-parameters>
				<generatedNs:xsl-parameter name="street" overridable="true">
					17, rue du Parc
				</generatedNs:xsl-parameter>
				<generatedNs:xsl-parameter name="city" overridable="false">
					Grenoble
				</generatedNs:xsl-parameter>
			</generatedNs:xsl-parameters>
		</jbi:provides>
	</jbi:services>
</jbi:jbi>

A JBI descriptor for an XSLT service-unit can only define one provides block.

A xsl-parameter element has the following structure:

<xs:complexType name="XslParameter">
	<xs:simpleContent>
		<xs:extension base="xs:string">
			<xs:attribute name="name" type="xs:string" />
			<xs:attribute name="overridable" type="xs:boolean" default="false" />
		</xs:extension>
	</xs:simpleContent>
</xs:complexType>

• Its value is a text.
• The name attribute must match the name of a XSL parameter.
• The overridable attribute defines whether this static value can be overriden by a dynamic value (from an incoming message).

Interceptor

Example of an interceptor configuration:

<?xml version="1.0" encoding="UTF-8"?>
<!--...-->
<petalsCDK:su-interceptors>
  <petalsCDK:send>
    <petalsCDK:interceptor name="myInterceptorName">
      <petalsCDK:param name="myParamName">myParamValue</petalsCDK:param>
      <petalsCDK:param name="myParamName2">myParamValue2</petalsCDK:param>
    </petalsCDK:interceptor>
  </petalsCDK:send>
  <petalsCDK:accept>
    <petalsCDK:interceptor name="myInterceptorName">
      <petalsCDK:param name="myParamName">myParamValue</petalsCDK:param>
    </petalsCDK:interceptor>
  </petalsCDK:accept>
  <petalsCDK:send-response>
    <petalsCDK:Interceptor name="myInterceptorName">
      <petalsCDK:param name="myParamName">myParamValue</petalsCDK:param>
    </petalsCDK:Interceptor>
  </petalsCDK:send-response>
  <petalsCDK:accept-response>
    <petalsCDK:Interceptor name="myInterceptorName">
      <petalsCDK:param name="myParamName">myParamValue</petalsCDK:param>
    </petalsCDK:Interceptor>
  </petalsCDK:accept-response>
</petalsCDK:su-interceptors>
<!--...-->

Service-Unit content

The service unit must contain the XSL style sheet.
It is also highly recommended to provide a WSDL description for this service.
This WSDL is not mandatory, but not providing it will prevent your service from interacting with other Petals services and components.

The archive may also embed a JAR containing the custom functions referenced in the XSL style sheet, if any.

The directory structure of a SU for the Petals-SE-XSLT looks like this:

su-xslt-TransformationName-provide.zip
   + META-INF
     - jbi.xml
   + XsltService.wsdl (recommended)
   + <XSL style sheet>.xsl
   + customFunctions.jar (optional)

Configuring the component

The component can be configured through its JBI descriptor file, as shown below.

<?xml version="1.0" encoding="UTF-8"?>
<jbi
	version="1.0"
	xmlns='http://java.sun.com/xml/ns/jbi'
	xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
	xmlns:petalsCDK="http://petals.ow2.org/components/extensions/version-5"
	xmlns:xslt="http://petals.ow2.org/components/xslt/version-2">

	<component type="service-engine">
		<identification>
			<name>petals-se-xslt</name>
			<description>A Xslt Service Engine</description>
		</identification>

		<component-class-name description="Xslt Component class">org.ow2.petals.se.xslt.XsltSe</component-class-name>
		<component-class-path><path-element/></component-class-path>
		<bootstrap-class-name>org.ow2.petals.component.framework.DefaultBootstrap</bootstrap-class-name>
		<bootstrap-class-path><path-element/></bootstrap-class-path>

		<petalsCDK:acceptor-pool-size>3</petalsCDK:acceptor-pool-size>
		<petalsCDK:processor-pool-size>10</petalsCDK:processor-pool-size>
		<petalsCDK:processor-max-pool-size>50</petalsCDK:processor-max-pool-size>
		<petalsCDK:ignored-status>DONE_AND_ERROR_IGNORED</petalsCDK:ignored-status>
		<petalsCDK:properties-file></petalsCDK:properties-file>
		<petalsCDK:notifications>false</petalsCDK:notifications>
		<petalsCDK:jbi-listener-class-name>org.ow2.petals.se.xslt.XsltJBIListener</petalsCDK:jbi-listener-class-name>
	</component>
</jbi>

The component configuration includes the configuration of the CDK. The following parameters correspond to the CDK configuration.

Definition of CDK parameter scope :

• Installation: The parameter can be set during the installation of the component, by using the installation MBean (see JBI specifications for details about the installation sequence). If the parameter is optional and has not been defined during the development of the component, it is not available at installation time.
• Runtime: The paramater can be set during the installation of the component and during runtime. The runtime configuration can be changed using the CDK custom MBean named RuntimeConfiguration. If the parameter is optional and has not been defined during the development of the component, it is not available at installation and runtime times.

Interceptor

Interceptors can be defined to inject some post or pre processing in the component during service processing.

Using interceptor is very sensitive and must be manipulate only by power users. An non properly coded interceptor engaged in a component can lead to uncontrolled behaviors, out of the standard process.

Example of an interceptor configuration:

<?xml version="1.0" encoding="UTF-8"?>
<!--...-->
<petalsCDK:component-interceptors>
  <petalsCDK:interceptor active="true" class="org.ow2.petals.myInterceptor" name="myInterceptorName">
    <petalsCDK:param name="myParamName">myParamValue</petalsCDK:param>
    <petalsCDK:param name="myParamName2">myParamValue2</petalsCDK:param>
  </petalsCDK:interceptor>
</petalsCDK:component-interceptors>
<!--...-->

This component does not have any specific configuration parameter.

Monitoring the component

Using metrics

Several probes providing metrics are included in the component, and are available through the JMX MBean 'org.ow2.petals:type=custom,name=monitoring_<component-id>', where <component-id> is the unique JBI identifier of the component.

Common metrics

The following metrics are provided through the Petals CDK, and are common to all components:

Dedicated metrics

No dedicated metric is available.

Receiving alerts

Several alerts are notified by the component through notification of the JMX MBean 'org.ow2.petals:type=custom,name=monitoring_<component-id>', where <component-id> is the unique JBI identifier of the component.

To integrate these alerts with Nagios, see Receiving Petals ESB defects in Nagios.

Common alerts

Dedicated alerts

No dedicated alert is available.