Drools- how to find out which all rules were matched?

Question

I've one .DRL file which has say 10 rules. Once I insert a fact, some rules may be matched- how do I find out which rules were matched programmatically?

Answer 1

Note that this answer is valid for versions of Drools up to 5.x. If you have moved on to 6 or above, then take a look at the modified answer from @melchoir55. I haven't tested it myself, but I'll trust that it works.

To keep track of rule activations, you can use an AgendaEventListener. Below is an example, as found here:

https://github.com/gratiartis/sctrcd-payment-validation-web/blob/master/src/main/java/com/sctrcd/drools/util/TrackingAgendaEventListener.java

You just need to create such a listener and attach it to the session like so:

ksession = kbase.newStatefulKnowledgeSession();
AgendaEventListener agendaEventListener = new TrackingAgendaEventListener();
ksession.addEventListener(agendaEventListener);
//...
ksession.fireAllRules();
//...
List<Activation> activations = agendaEventListener.getActivationList();

Note that there is also WorkingMemoryEventListener which enables you to do the same with tracking insertions, updates and retractions of facts.

Code for a tracking & logging AgendaEventListener:

package com.sctrcd.drools.util;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import org.drools.definition.rule.Rule;
import org.drools.event.rule.DefaultAgendaEventListener;
import org.drools.event.rule.AfterActivationFiredEvent;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * A listener that will track all rule firings in a session.
 * 
 * @author Stephen Masters
 */
public class TrackingAgendaEventListener extends DefaultAgendaEventListener {

    private static Logger log = LoggerFactory.getLogger(TrackingAgendaEventListener.class);

    private List<Activation> activationList = new ArrayList<Activation>();

    @Override
    public void afterActivationFired(AfterActivationFiredEvent event) {
        Rule rule = event.getActivation().getRule();

        String ruleName = rule.getName();
        Map<String, Object> ruleMetaDataMap = rule.getMetaData();

        activationList.add(new Activation(ruleName));
        StringBuilder sb = new StringBuilder("Rule fired: " + ruleName);

        if (ruleMetaDataMap.size() > 0) {
            sb.append("\n  With [" + ruleMetaDataMap.size() + "] meta-data:");
            for (String key : ruleMetaDataMap.keySet()) {
                sb.append("\n    key=" + key + ", value="
                        + ruleMetaDataMap.get(key));
            }
        }

        log.debug(sb.toString());
    }

    public boolean isRuleFired(String ruleName) {
        for (Activation a : activationList) {
            if (a.getRuleName().equals(ruleName)) {
                return true;
            }
        }
        return false;
    }

    public void reset() {
        activationList.clear();
    }

    public final List<Activation> getActivationList() {
        return activationList;
    }

    public String activationsToString() {
        if (activationList.size() == 0) {
            return "No activations occurred.";
        } else {
            StringBuilder sb = new StringBuilder("Activations: ");
            for (Activation activation : activationList) {
                sb.append("\n  rule: ").append(activation.getRuleName());
            }
            return sb.toString();
        }
    }

}