[rules-users] NPE from LHS of rule is not returned by Drools to calling program

[Wolfgang Laun]

But isn't the java.lang.runtimeException thrown up to the point where you
call fireAllrules() in your RulesEngine.java at line 318? Just catching NPE
is a little dodgy since you can't know what might happen.
-W

On 28 March 2012 18:35, scottleff <scott.leff at fbfs.com> wrote:

> During development of our Drools rule base I had a case where a rule
> compiled
> fine, but at runtime a NPE is thrown by MVEL when applying the predicate
> (LHS) because the Coverage.vehicleSupplement attribute was NULL.  I had
> expected the NPE to be returned to my calling java program so that my
> try/catch could address the issue.  However, the exception was sent to
> System.err and the rule was simply skipped.  First, is the the default
> behavior in Drools for Exceptions thrown from the LHS?  If so, can it be
> overridden to actually return the exception?
>
> rule "BR--UM Stacked Coverage"
>        agenda-group "BR_Change"
>        dialect "mvel"
>        when
>                coverage : Coverage( vehicleSupplement.stackable == true ,
> coverageCode ==
> "UDCSL")
>                vehicle : Vehicle( unitAtRiskNumber : unitAtRiskNumber)
>                Policy( state == "NM" )
>        then
>                WorkItemReason fact0 = new WorkItemReason();
>                fact0.setType( "Policy" );
>                fact0.setReason( "6408: UM/UDM stacking change" );
>                fact0.setAddBookmark( "VE" );
>                fact0.setAddBookmarkUnit( unitAtRiskNumber );
>                insertLogical(fact0 );
> end
>
> *Here is the stacktrace from my console:*
> WARNING: java.lang.RuntimeException: cannot invoke getter:
> getVehicleSupplement [declr.class: com.fbfs.pc.ecd.model.Coverage;
> act.class: com.fbfs.pc.ecd.model.Coverage] (see trace)
>        at
>
> org.mvel2.optimizers.impl.refl.nodes.GetterAccessor.getValue(GetterAccessor.java:74)
>        at
> org.mvel2.ast.ASTNode.getReducedValueAccelerated(ASTNode.java:106)
>        at org.mvel2.MVELRuntime.execute(MVELRuntime.java:87)
>        at
> org.mvel2.compiler.CompiledExpression.getValue(CompiledExpression.java:122)
>        at org.mvel2.MVEL.executeExpression(MVEL.java:954)
>        at
>
> org.drools.base.extractors.MVELClassFieldReader.getValue(MVELClassFieldReader.java:100)
>        at
>
> org.drools.base.extractors.BaseObjectClassFieldReader.isNullValue(BaseObjectClassFieldReader.java:179)
>        at
>
> org.drools.base.evaluators.EqualityEvaluatorsDefinition$BooleanEqualEvaluator.evaluate(EqualityEvaluatorsDefinition.java:555)
>        at
> org.drools.rule.LiteralRestriction.isAllowed(LiteralRestriction.java:87)
>        at
> org.drools.rule.LiteralConstraint.isAllowed(LiteralConstraint.java:109)
>        at org.drools.reteoo.AlphaNode.assertObject(AlphaNode.java:130)
>        at
>
> org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:458)
>        at
>
> org.drools.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:386)
>        at
> org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:215)
>        at
> org.drools.reteoo.EntryPointNode.assertObject(EntryPointNode.java:244)
>        at
> org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:330)
>        at
> org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:291)
>        at
>
> org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:886)
>        at
>
> org.drools.base.DefaultKnowledgeHelper.insert(DefaultKnowledgeHelper.java:180)
>        at
>
> org.drools.base.DefaultKnowledgeHelper.insert(DefaultKnowledgeHelper.java:174)
>        at
>
> PolicyDefinitionRules.Rule_policyDefinition_UnitAtRiskCoverage.defaultConsequence(Rule_policyDefinition_UnitAtRiskCoverage.java:8)
>        at
>
> PolicyDefinitionRules.Rule_policyDefinition_UnitAtRiskCoverageDefaultConsequenceInvoker.evaluate(Unknown
> Source)
>        at
> org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:1091)
>        at
> org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:1029)
>        at
> org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1251)
>        at
>
> org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:708)
>        at
>
> org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:672)
>        at
>
> org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:218)
>        at
>
> com.fbfs.pc.rulesengine.controller.RulesEngine.runRulesEngine(RulesEngine.java:318)
>
>
> My expectation that Exceptions thrown from the consequence (RHS) are
> returned to the calling program was confirmed when I added the following 2
> lines to a rule that was not experiencing the above issue:
>     String myString = null;
>     System.out.println(myString.trim());
>
> Is there any good documentation on Drools exception handling?
> Current configuration is Drools 5.3.0, MVEL 2.1.0, Glassfish 2.1
>
> --
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> Sent from the Drools: User forum mailing list archive at Nabble.com.
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