Exception handling at individual rule level - Drools

Question

How to catch and handle exceptions at individual rule level in Drools?

Aim is that exceptions at a single rule should not impact the execution of the rest of the rules.

I know that we can use try catch in RHS, but can we have a control at much higher level irrespective of what LHS or RHS is.

Something like:

fireAllRules( new DefaultAgendaEventListener() {
    @Override
        public void whenExceptionAtRule(Exception exception) {
            //handle exception when 
        }
})

Answer 1

First, you need to implement the org.kie.api.runtime.rule.ConsequenceExceptionHandler interface:

package sample;

public class MyConsequenceExceptionHandler implements ConsequenceExceptionHandler {

    @Override
    public void handleException(Match match, RuleRuntime rr, Exception excptn) {
        //Do whatever you want
    }

}

Then, it all depends on how are you creating your KieBases. If you are doing it manually (without using a kmodule.xml file), then you need to create a KieBaseConfiguration to specify what class you want to use to handle exceptions:

KieBaseConfiguration kconfig = new RuleBaseConfiguration();
kconfig.setProperty(ConsequenceExceptionHandlerOption.PROPERTY_NAME, "sample.MyConsequenceExceptionHandler");

And then use this kconfig object when creating your KieBase:

KieSession ksession = kcontainer.newKieBase(kconfig).newKieSession();

I couldn't find a declarative way to register the handler in the kmodule.xml file though.

Hope it helps,