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* <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> 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:* [EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]> [
mailto:[EMAIL PROTECTED] *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* <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> 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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