流口水总是真正的规则只触发一次

Question

I have these 2 rules :

rule "challenge 1" salience 10
    when
        ClientTransaction(amount < 30)
    then
        challenge.setChallenge("challenge1");
end

rule "challenge 2" salience 0
    when
        eval( true )
    then
        challenge.setChallenge("challenge2");
end

and this java code :

public class ComputeChallengeDroolsRulesImplementation implements IComputeChallenge {
    private KieServices kieServices = KieServices.Factory.get();
    private KieSession kieSession = getKieSession();
    private static final String RULES_PATH = "rules/";

    public KieFileSystem getKieFileSystem() throws IOException {
        KieFileSystem kieFileSystem = kieServices.newKieFileSystem();
        String[] rules = new File(getClass().getClassLoader().getResource(RULES_PATH).getFile()).list();
        for (String rule : rules) {
            kieFileSystem.write(ResourceFactory.newClassPathResource(RULES_PATH + rule));
        }
        return kieFileSystem;
    }

    public KieContainer getKieContainer() throws IOException {
        getKieRepository();

        KieBuilder kb = kieServices.newKieBuilder(getKieFileSystem());
        kb.buildAll();

        KieModule kieModule = kb.getKieModule();
        KieContainer kContainer = kieServices.newKieContainer(kieModule.getReleaseId());

        return kContainer;
    }

    public void getKieRepository() {
        final KieRepository kieRepository = kieServices.getRepository();
        kieRepository.addKieModule(
                new KieModule() {
                    public ReleaseId getReleaseId() {
                        return kieRepository.getDefaultReleaseId();
                    }
                });
    }

    @Bean
    public KieSession getKieSession() {
        try {
            return getKieContainer().newKieSession();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public Challenge2 computeChallenge(ClientTransaction clientTransaction) {
        kieSession.insert(clientTransaction);
        Challenge2 challenge = new Challenge2();
        kieSession.setGlobal("challenge", challenge);
        kieSession.fireAllRules();
        return challenge;
    }

}

here is the ClientTransation class :

public class ClientTransaction {
  private String id;
  private String merchant;
  private double amount;

  public ClientTransaction() {
  }

  public ClientTransaction(String id, String merchant, double amount) {
    this.id = id;
    this.merchant = merchant;
    this.amount = amount;
  }

  public String getId() {
    return id;
  }

  public void setId(String id) {
    this.id = id;
  }

  public String getMerchant() {
    return merchant;
  }

  public void setMerchant(String merchant) {
    this.merchant = merchant;
  }

  public double getAmount() {
    return amount;
  }

  public void setAmount(double amount) {
    this.amount = amount;
  }
}

And here is the Challenge2 class :

public class Challenge2 {
  private String challenge;

  public Challenge2() {
  }

  public Challenge2(String challenge) {
    this.challenge = challenge;
  }

  public String getChallenge() {
    return challenge;
  }

  public void setChallenge(String challenge) {
    this.challenge = challenge;
  }
}

when i call ComputeChallengeDroolsRulesImplementation.computeChallenge with an amount < 30 multiple times, it does return a challence object with a "challenge1" value multiple times as expected.

But when i call ComputeChallengeDroolsRulesImplementation.computeChallenge with an amount >= 30 multiple times, the first time it does return a "challenge2" value, but every subsequent time it return a Challenge2 object with a null value ?

Am i doing something wrong ?

Thank you

Answer 1

I am assuming you want to fire challenge 2 rule only when ClientTransaction event occurs. You can add a no condition check on a rule based on the occurrence of an event by just calling default constructor in the when part of a drool rule. Try changing you challenge 2 rule as below:

rule "challenge 2" salience 0
    when
        ClientTransaction()
    then
        challenge.setChallenge("challenge2");
end

Also, it is not recommended to use eval so much in the drools rule. To more about best practices, check here

Answer 2

As the following documentation states: https://docs.jboss.org/drools/release/5.2.0.Final/drools-expert-docs/html/ch05.html#d0e3313

The engine cannot be notified about value changes of globals and does not track their changes. Incorrect use of globals in constraints may yield surprising results - surprising in a bad way.

[…]

Globals are not designed to share data between rules and they should never be used for that purpose. Rules always reason and react to the working memory state, so if you want to pass data from rule to rule, assert the data as facts into the working memory.

It is strongly discouraged to set or change a global value from inside your rules . We recommend to you always set the value from your application using the working memory interface.