Handling Exceptions in Drools Files

问题

How do we handle exceptions in Drools files?

Example: My rule uses a shared Java method.

rule "002.17.1"
    dialect "mvel"
    when
        comp : Component()
    then        
        boolean validstate = SharedCodeUtil.hasValidateStateCountryUS(comp.address);

        errors.add(new ValidationFailure("002.17.1", comp.getSubApplicationGroupID(), comp.getSubApplicationID(),tokens));

end

Java method SharedCodeUtil, may have exceptions:

    if (m != null)
    {
        try
        {
            Object o = m.invoke(form,(Object[])null);
            if(BudgetType.Project.equals(o))
                count++;
        }
        catch (Exception e)
        {
            LOG.error("Error", e);
            // re-throw? who will catch?
        }

There's an Exception condition in the shared Java method called by the Drools file. Who is going to catch it, and what else should I do besides logging it?

回答1:

There is no particular problem with catching exceptions on the right hand side of a rule: this is Java code.

when
    //...
then
    try { /* some code */
    } catch( SomeException ex ){ /* handle ex */ }
end

Whether you need to re-throw is a design decision, depending on the kind of exception. If reflection goes wrong, you have a fundamental problem in the code, and continuation is very likely pointless. If you rethrow, the next level is where the rule engine is called:

try {
    kSession.fireAllRules();
} catch( Exception e ){
    //... handle exception
}

You'll probably have to terminate the application after logging a severe error.

The situation is different when exceptions are thrown in code that is executed during rule evaluation. This cannot be caught "inside", and it will unwind to a handler around fireAllRules.

Note that negative validation results should better not be propagated via exceptions.

来源：https://stackoverflow.com/questions/28481600/handling-exceptions-in-drools-files

标签

drools