ServiceMix Drools

The ServiceMix Drools component provides JBI integration to the Drools Rules Engine.

It can be used to deploy a rules set that will implement a router or an actual service.

A router will mostly act as a transparent proxy between the consumer and the target service provider mad will mostly be implemented by the jbi.route(uri) method below. This method creates a new exchange identical to the one received by the component and will send it to the specified destination. You can also send back a Fault if needed. A router can also be implemented by using directly the JBI Apis (available with the jbi helper) by using the provided client.

This component can also be used to implement a real service, as shown in the Fibonnacci example. The service can act as a consumer and create / send exchanges by using the client provided by the jbi helper.

Maven Archetype

You can create a Drools Service Unit using the servicemix-drools-service-unit Maven archetype:

mvn archetype:create \
  -DarchetypeGroupId=org.apache.servicemix.tooling \
  -DarchetypeArtifactId=servicemix-drools-service-unit \
  -DarchetypeVersion=2010.01 \
  -DgroupId=your.group.id \
  -DartifactId=your.artifact.id \
  -Dversion=your-version

Once you've customized the service unit, simply install the SU:

mvn install

Remember that to be deployable in ServiceMix, the ServiceUnit has to be embedded in a Service Assembly: only the Service Assembly zip file can be deployed in ServiceMix.
To add your SU in a SA, you need to define it in the dependency sets:

<dependency>
  <groupId>your.group.id</groupId>
  <artifactId>your.artifact.id</artifactId>
  <version>your-version</version>
</dependency>

Endpoint Configuration

<beans xmlns:drools="http://servicemix.apache.org/drools/1.0"
       xmlns:replaceMe="http://servicemix.apache.org/replaceMe">

  <drools:endpoint service="replaceMe:serviceName" endpoint="drools"
    ruleBaseResource="classpath:router.drl"
    namespaceContext="#nsContext"/>

  <drools:namespace-context id="nsContext">
    <drools:namespaces>
      <drools:namespace prefix="bar">http://servicemix.apache.org/bar</drools:namespace>
    </drools:namespaces>
  </drools:namespace-context>

</beans>

Endpoint Attributes

Name	Type	Description	Required
endpoint	String	JBI Endpoint Name	no (will be auto-generated if not specified
service	QName	JBI Server Name	no (will be auto-generated if not specified)
ruleBaseResource	URL	DRL File	The path to the DRL file	yes
namespaceContext	namespace-context bean	Drool Namespace Context	no

JBI Helper

DRL files deployed to the servicemix-drools engine have access to a JbiHelper class in a global variable named jbi which provides the following attributes and methods:

Attribute	Description
jbi.getEndpoint()	The `DroolsEndpoint` using this DRL
jbi.getContent()	A `ComponentContext` for this endpoint
jbi.getChannel()	A `DeliveryChannel` for this endpoint (no accept allowed)
jbi.getClient()	A `ServiceMixClient` on top of this endpoint
jbi.getExchange()	The `Exchange` received
jbi.getLogger()	A `org.apache.commons.logging.Log` logger

Methods	Description
jbi.route(uri)	Route the current exchange to the given uri
jbi.fault(content)	Returns a fault using the given string as the xml fault
jbi.answer(content)	Sends an Out message using the given string as the xml content

The received exchange is added as a fact to the working memory.
Note that, due to Drools limited support for non simple java beans accessors, the JBI MessageExchange and NormalizedMessage are wrapped with simple beans.

Injecting additional beans in the rules

The JbiHelper is injected by the component itself so that you can access the current exchange and handle it. However, there are cases where you need to add your own beans and inject them in the rules definition. Starting from ServiceMix 3.2, this is now possible using the following syntax:

<drools:endpoint  service="test:service"
                  endpoint="endpoint"
                  ruleBaseResource="classpath:router.drl"
                  globals="#globals" />
<util:map id="globals">
  <entry key="helper" value-ref="helper" />
</util:map>
<bean id="helper" class="org.example.Helper" />

In the rules definition, just add:

global org.example.Helper helper;

Don't forget to add the namespace for the util element.

xmlns:util="http://www.springframework.org/schema/util"

Then you can use it from your rules ...

Router

Endpoint definition

<drools:endpoint  service="test:service"
                  endpoint="endpoint"
                  ruleBaseResource="classpath:router.drl" />

Rules definitions

package org.apache.servicemix.drools
 
import org.apache.servicemix.drools.model.Exchange;

global org.apache.servicemix.drools.model.JbiHelper jbi;
 
rule "Unspecified id"
	when
		me : Exchange( status == Exchange.ACTIVE, in : in != null )
		eval( in.xpath("/test/@id <= 0") )
	then
		jbi.fault( "<fault>Id must be > 0</fault>" );
end

rule "Route to target1"
	when
		me : Exchange( status == Exchange.ACTIVE, in : in != null )
		eval( in.xpath("/test/@id = 1") )
	then
		jbi.route( "service::target1" );
end

rule "Route to target2"
	when
		me : Exchange( status == Exchange.ACTIVE, in : in != null )
		eval( in.xpath("/test/@id = 2") )
	then
		jbi.route( "service::target2" );
end

rule "Route to target3"
	when
		me : Exchange( status == Exchange.ACTIVE, in : in != null )
		eval( in.getProperty("prop") != null )
	then
		jbi.route( "service::target3" );
end

Child pages

servicemix-drools