[rules-users] How to catch Exceptions when firing rules
Yang Song
starsy at gmail.com
Sat Aug 25 00:15:05 EDT 2007
Mark, Michael, Edson and all,
Thanks very much for participating into this discussion. I am so glad to see
that the response has quickly been turned out into an output. Really
appreciate your help, Mark.
Sorry may be a liittle too aggressive, but here comes another thought of
mine: if we can have the RHS to have exception handler, why not the LHS has
exception handler too? This is sometimes very helpful when someone abuses
eval() in LHS.
Best Regards,
Yang
On 8/25/07, Mark Proctor <mproctor at codehaus.org> wrote:
>
> Here is the unit test showing how it works, this uses the programmatic
> api, you can also use the drools.consequenceExceptionHandler property.
> This will be in the 4.0.1 release, which is out this monday.
> http://jira.jboss.org/jira/browse/JBRULES-1123
>
> public void testCustomConsequenceException() throws Exception {
>
> final PackageBuilder builder = new PackageBuilder();
> builder.addPackageFromDrl( new InputStreamReader(
> getClass().getResourceAsStream( "test_ConsequenceException.drl" ) ) );
> final Package pkg = builder.getPackage();
>
> RuleBaseConfiguration conf = new RuleBaseConfiguration();
> CustomConsequenceExceptionHandler handler = new
> CustomConsequenceExceptionHandler();
> conf.setConsequenceExceptionHandler( handler );
>
> final RuleBase ruleBase = getRuleBase(conf);
> ruleBase.addPackage( pkg );
> final WorkingMemory workingMemory = ruleBase.newStatefulSession();
>
> final Cheese brie = new Cheese( "brie",
> 12 );
> workingMemory.insert( brie );
>
> workingMemory.fireAllRules();
>
> assertTrue( handler.isCalled() );
> }
>
> public static class CustomConsequenceExceptionHandler implements
> ConsequenceExceptionHandler {
>
> private boolean called;
>
> public void handleException(Activation activation,
> WorkingMemory workingMemory,
> Exception exception) {
> this.called = true;
> }
>
> public boolean isCalled() {
> return this.called;
> }
> }
>
> Mark
> Mark Proctor wrote:
>
> ok I have added a ConsequenceExceptionHandler to RuleBaseConfiguration,
> default just wraps and re-throws as a runtime exception. You can override
> this to provide a custom consequence exception handler. But do be aware that
> if you swallow the working memory integrity may be invalid, if the error
> happened during a working memory action.
>
> Mark
> Anstis, Michael (M.) wrote:
>
> For what it's worth I think this would be a good idea too.
>
> Perhaps the default ASM wrapper around the RHS could use a try...catch
> block and log any exceptions of a rules' activation in a (drools) accessible
> log? Heck you could even allow certain accepted exceptions to be defined as
> a property of the rule; and any other non-defined exception types cause the
> session to become invalidated. If we're ever to let "the business" define
> rules we need to accept they might make mistakes that we're better off
> capturing and report back than invalidate the whole session. Why should a
> whole session be invalidated because a single rule activation failed anyway?
>
> With kind regards,
>
> Mike
>
> ------------------------------
> *From:* rules-users-bounces at lists.jboss.org [
> mailto:rules-users-bounces at lists.jboss.org<rules-users-bounces at lists.jboss.org>]
> *On Behalf Of *Yang Song
> *Sent:* 24 August 2007 16:16
> *To:* Rules Users List
> *Subject:* Re: [rules-users] How to catch Exceptions when firing rules
>
>
> Thanks a lot for the answer, Mark. But I don't think it makes sense.
>
> Because in some scenarios, you cannot guarantee the consequence part of
> rule is 100% correct -- there could be errors happening in run-time which
> are hard to predict, especially when a complex action or logic will be
> executed as the concequece.
>
> There should at least be some mechanisms to tell whoever fires the rule
> that there is something wrong during the rule firing process, then and
> he can do something, e.g. create a new session. Also it should enable
> the rule firer to catch these exceptions and do the clean up work silently
> -- instead of leaving these things on the stderr even cannot be seen in the
> logs. This will make the program depending on the JBoss Rules to be more
> robust.
>
> What do you think? If JBoss Rules already has the ability to do this job,
> can you please let me know?
>
> Thanks again,
> Yang
>
>
> On 8/24/07, Mark Proctor <mproctor at codehaus.org> wrote:
> >
> > Once an exception is thrown on a conseuqence the current session is
> > considered invalid. You'll need to add the try catch inside of the actual
> > consequence.
> >
> > Mark
> > Yang Song wrote:
> >
> > Hi,
> >
> > Anyone knows how to catch the exception when firing the rules?
> >
> > I wrapped the session.fireAllRules() method using try...catch, however
> > it doesn't work: when someone wrote bad code in the rule's action part, the
> > Exception will be thrown and printed to the stderr, and this will make the
> > rule engine stop working -- the try...catch outside doesn't help anything.
> >
> > If the exception thrown from the rule's action part can be caught
> > externally, the system can be protected from interrupting Exception.
> >
> > try {
> > _log.debug("Firing rules in : " + getName());
> >
> > session.fireAllRules();
> >
> > } catch (Exception e) {
> > _log.info("Error when firing rules: ", e);
> > }
> >
> > Thanks,
> > Yang
> >
> > ------------------------------
> >
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> >
> >
> >
> >
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