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ServiceMix Drools

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

This Service Engine 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.

Note that this component is only available in releases >= 3.1 and deprecate the older lightweight Drools component

JbiHelper

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