[rules-users] Class Cast Exception in Drools 4 Generated Accumulate Method

[Steve Ronderos]

Hi Rules Users,

I'm experiencing an issue with a Drools 4.0.7 rule.

Here is a clip of the exception that is thrown:

Caused by: org.mvel.CompileException: cannot invoke method
        at 
org.mvel.optimizers.impl.refl.MethodAccessor.getValue(MethodAccessor.java:54)
        at 
org.mvel.optimizers.impl.refl.VariableAccessor.getValue(VariableAccessor.java:39)
        at 
org.mvel.ast.VariableDeepPropertyNode.getReducedValueAccelerated(VariableDeepPropertyNode.java:22)
        at 
org.mvel.ast.PropertyASTNode.getReducedValueAccelerated(PropertyASTNode.java:21)
        at org.mvel.MVELRuntime.execute(MVELRuntime.java:90)
        at 
org.mvel.CompiledExpression.getValue(CompiledExpression.java:111)
        at org.mvel.MVEL.executeExpression(MVEL.java:235)
        at 
org.drools.base.mvel.MVELConsequence.evaluate(MVELConsequence.java:48)
        at 
org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:554)
        ... 80 more
Caused by: java.lang.reflect.InvocationTargetException
        at sun.reflect.GeneratedMethodAccessor412.invoke(Unknown Source)
        at 
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:585)
        at 
org.mvel.optimizers.impl.refl.MethodAccessor.getValue(MethodAccessor.java:46)
        ... 88 more
Caused by: org.drools.RuntimeDroolsException: 
java.lang.ClassCastException: com.demo.Rule_My_Rule_0$Accumulate0
        at org.drools.rule.Accumulate.accumulate(Accumulate.java:131)
        at 
org.drools.reteoo.AccumulateNode.modifyTuple(AccumulateNode.java:352)
        at 
org.drools.reteoo.AccumulateNode.assertObject(AccumulateNode.java:248)
        at 
org.drools.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:318)
        at 
org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:162)
        at org.drools.reteoo.Rete.assertObject(Rete.java:175)
        at 
org.drools.reteoo.ReteooRuleBase.assertObject(ReteooRuleBase.java:192)
        at 
org.drools.reteoo.ReteooWorkingMemory.doInsert(ReteooWorkingMemory.java:71)
        at 
org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:911)
        at 
org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:883)
        at 
org.drools.base.DefaultKnowledgeHelper.insert(DefaultKnowledgeHelper.java:67)
        at 
org.drools.base.DefaultKnowledgeHelper.insert(DefaultKnowledgeHelper.java:61)
        ... 92 more
Caused by: java.lang.ClassCastException: 
com.demo.Rule_My_Rule_0$Accumulate0
        at 
com.demo.Rule_My_Rule_0Accumulate0Invoker.accumulate(Rule_My_Rule_0Accumulate0Invoker.java:43)
        at org.drools.rule.Accumulate.accumulate(Accumulate.java:123)
        ... 103 more

The actually rule name and package are a lot longer, I changed them here 
for brevity and because I don't believe the names themselves are relevant.

This exception is being thrown intermittently when this rule, which 
contains an accumulate function is called.  I say intermittently because 
it does not happen every time the rule is run.  As far as I can tell the 
ClassCastExceptions only happens when the computer that the rules are 
running on is under load.

A few more details before I post the rule itself.  The rule base that I am 
building consists of 2 drl files.  Both of the files have the same package 
declaration at the top.  The 2 packages are built separately using 
PackageBuilder then combined using RuleBase.addPackage() on both packages. 
 Also, I'm not sure if this is relevant, but this scenario takes place in 
a web application where the two package objects are only built once (for 
performance) but each user session creates a new RuleBase and adds the 
packages.  The individual sessions then create stateful sessions from the 
rule base.

This is the rule that I believe is causing the issue.

rule "My Rule"
    salience 50
    dialect "java"
    no-loop true
    when
        $module : Module( selected == false, required > 1, $size : 
required )
        $list : ArrayList( )
                from accumulate( PotentialMatch( module == $module, $slot 
: slot ),
                    init( List result = new ArrayList(); ),
                    action( result.add($slot); ),
                    reverse( result.remove((Integer)$slot ); ),
                    result( result ) )
        eval( countThem($list, $size) != $module.setMatchCount() )
    then
        modify( $module ) { setMatchCount(countThem($list, $size)) };
end

As I'm typing this I realize that there is another way to write this rule 
using collect.  I'm not sure why it was written this way, but since I have 
already come this far, has anyone had any experience with the Drools 4 
generated code throwing ClassCastExceptions? 

Thanks,

Steve Ronderos
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