[rules-users] How to catch Exceptions when firing rules
Mark Proctor
mproctor at codehaus.org
Sat Aug 25 08:02:51 EDT 2007
There is no way you can recover from an exception on the LHS, so that
makes me reluctant to allow users to create something that swallows
exceptions. If you worried about it, put a try catch around the inserts.
Mark
Yang Song wrote:
>
> 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
> <mailto: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> [
>>> mailto: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
>>> <mailto: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
>>>>
>>>> ------------------------------------------------------------------------
>>>>
>>>> _______________________________________________
>>>> rules-users mailing list
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>>>> https://lists.jboss.org/mailman/listinfo/rules-users
>>>>
>>>
>>>
>>>
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>>
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