How to use Spring managed beans in Drool

Question

I have a service that is managed by spring and I want to use or inject as dependency in drool rule. How can I use the service bean in the Drool rule?

@Service 
public class SomeService {

     public void doSomething() {}
}



dialect "mvel"

rule "something"
    when
       ................
    then 
       service.doSomething()
end

Answer 1

Pass your bean instance into working memory when you invoke them, the same as you'd pass any other data in. This way you can autowire or otherwise leverage dependency injection to get your Spring-managed singleton bean, and then use that same bean in your rules without having to new up another instance.

@Component
class RuleExecutor {

  private final SomeService service; // Bean set via constructor injection

  public RuleExecutor(SomeService service) {
    this.service = service;
  }

  public void fireRules( ... ) { // assuming other data passed in via parameter
    KieSession kieSession = ...; 
    kieSession.insert( this.service); // insert bean into the working memory
    kieSession.insert( ... );  // insert other data into working memory
    kieSession.fireAllRules();
  }
}

In this example I used constructor injection to pass in the bean instance. We can assume that both the @Service and this @Component were picked up by the component scan.

Then you could interact with it in the rules in the same way as you'd do any other data:

dialect "mvel"

rule "something"
when
  service: SomeService()
then 
  service.doSomething()
end

Remember that service: SomeService() matches an instance of SomeService in working memory and assigns it to the service variable for use in the rule. It does not new up a new instance.