How to call method in spring bean from drools rule

Question

I have a Drools rule that checks if a value exists in the database. But before I check I need to pass the value to a spring bean method to encrypt before checking the value, because the values in the database are encrypted.

Service

public class EncryptService {
    public String encrypt(String value) {
    return encryptedValue;
    }
}

Rule

rule "Check value"
    salience 10
    dialect "java"
     when
        $g: EncryptService()
        exists($g.encrypt(value))
     then
        log.info('value already exists')
end

How can I call that method to encrypt from the rule for a Spring Bean?

Things I have tried

Declaring via a global variable. instantiating via new like in the example above, but that won't work because it's a bean that was already created by spring.

Answer 1

You need to pass the bean instance into your rule session, then the rule as written would do what you want it to.

For example --

@Component
class RuleExecutor {

  private final EncryptService encryptService; // Bean set via constructor injection

  public RuleExecutor(EncryptService encryptService) {
    this.encryptService = encryptService;
  }

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

Then you could do things against your bean instance in your rules:

rule "Encrypt value"
when
  SomeInput( $originalValue: value )
  $e: EncryptService() // will match the bean instance in working memory
then
  String encrypted = $e.encrypt($originalValue);
  // do stuff with encrypted value, eg: insert(encrypted)
end

The syntax $e: EncryptService() doesn't new up an instance. It matches an existing instance of EncryptService in working memory with no other restrictions. It's the same logic as you would do something like $car: Car( doors == 4, color == "red") -- this doesn't create a new instance of Car with those variables, it finds an instance of Car with those restrictions in working memory and assigns them to the variable $car.