6.6. Content Based Routing Using the JBoss Rules Engine

JBoss Rules is the rule provider "engine" for the content-based router. The Enterprise Service Bus integrates with this engine through three different routing action classes, these being:
  • a routing rule set, written in the JBoss Rules engine's DRL language (alternatively, you can use the DSL language if you prefer it);
  • the message content. This is the data that goes into the JBoss Rules engine (it comes in either XML format or as objects embedded in the message);
  • the destination (which is derived from the resultant information coming out of the engine).


When a message is sent to the content-based router, a rule-set will evaluate its content and return a set of service destinations.
  • org.jboss.soa.esb.actions.ContentBasedRouter: This action class implements the content-based routing pattern. It routes a message to one or more destination services, based on the message content and the rule set against which it is evaluating that content. The content-based router throws an exception when no destinations are matched for a given rule set or message combination. This action will terminate any further pipeline processing, so always position it last in your pipeline.
  • org.jboss.soa.esb.actions.ContentBasedWiretap: This implements the WireTap pattern. The WireTap is an enterprise integration pattern that sends a copy of the message to a control channel. The WireTap is identical in functionality to the standard content-based router, however it does not terminate the pipeline. It is this latter characteristic which makes it suitable to be used as a wire-tap, hence its name. For more information, see http://www.eaipatterns.com/WireTap.html.
  • org.jboss.soa.esb.actions.MessageFilter: This implements the message filter pattern. The message filter pattern is used in cases where messages can simply be dropped if certain content requirements are not met. In other words, it functions identically to the content-based router except that it does not throw an exception if the rule set does not match any destinations, it simply filters the message out. For more information, see http://www.eaipatterns.com/Filter.html.