Drools: Declared Types (Blog)

AlertingService.drl.java

package com.acme;
unit AlertingService;
rule IncomingEvent when
   // matches when a temperature higher than 30 °C is registered (OOPath syntax)
   $e : /events [ type == "temperature", value >= 30 ] // Temperature is an Event subclass
then
   System.out.println("incoming event: "+ $e.getMessage());
   alerts.append( new Alert( "warning", $e ) );
end

AlertingService.java

package com.acme;
public class AlertingService implements RuleUnitData {
   private final DataStream<Event> events = DataSource.createStream();
   private final DataStream<Alert> alerts = DataSource.createStream();
   // getters and setters
}

full.drl.java

package com.acme;

declare Event
   type:  String
   value: int
end

declare Alert
  severity: String
  message:  String
end

declare AlertingService extends RuleUnitData
   events: DataStream<Event>
   alerts: DataStream<Alert>
end

unit AlertingService;

rule IncomingEvent when
   // matches when a temperature higher than 30 °C is registered (OOPath syntax)
   $e : /events [ type == "temperature", value >= 30 ] // Temperature is an Event subclass
then
   System.out.println("incoming event: "+ $e.getMessage());
   alerts.append( new Alert( "warning", $e ) );
end

query Warnings
   alerts: /alerts [ severity == "warning" ]
end

GenericTypeDef.drl.java

package com.acme;
declare AlertingService extends RuleUnitData
   events: DataStream<Event>
   alerts: DataStream<Alert>
end

TypeDef.drl.java

package com.acme;

declare Event
   type:  String
   value: int
end

declare Alert
  severity: String
  message:  String
end