[jboss-jira] [JBoss JIRA] (DROOLS-185) ClassCastException at ConditionEvaluator

[Liu Yan (JIRA)]

    [ https://issues.jboss.org/browse/DROOLS-185?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13034269#comment-13034269 ] 

Liu Yan edited comment on DROOLS-185 at 1/22/15 1:50 AM:
---------------------------------------------------------

In hope my case could help you and others, I past some pseud code here:

In java:
ClassA extends ClassBase
ClassB extends ClassBase

In DRL:
rule prepare
  when
		$base: ClassBase()
	then
		update($base);
end

rule process
	when
		$B: ClassB()
	then
		$B.doThings_ClassB_Specific()
end

The CCE would likely be something like ClassA can't cast to ClassB at update($base) in rule prepare.
When I first saw this, it's pretty odd because ClassA never appeared anywhere. My work was blocked here for 2 days, finally I tried to comment out "rule process" and the CCE disappeared. This give me some idea of how this happen.


was (Author: oscar_cqu):
In hope my case could help you and others, I past some pseud code here:

In java:
ClassA extends ClassBase
ClassB extends ClassBase

In DRL:
rule prepare
  when
		$base: ClassBase()
	then
		update($base);
end

rule process
	when
		$B: ClassB()
	then
		$B.doThings_ClassB_Specific()
end

The CCE would likely be something like ClassB can't cast to ClassA at update($base) in rule prepare.
When I first saw this, it's pretty odd because ClassA never appeared anywhere. My work was blocked here for 2 days, finally I tried to comment out "rule process" and the CCE disappeared. This give me some idea of how this happen.

> ClassCastException at ConditionEvaluator
> ----------------------------------------
>
>                 Key: DROOLS-185
>                 URL: https://issues.jboss.org/browse/DROOLS-185
>             Project: Drools
>          Issue Type: Bug
>    Affects Versions: 5.5.0.Final
>            Reporter: Sergey Alaev
>            Assignee: Mario Fusco
>
> Stacktrace:
> Caused by: java.lang.ClassCastException: ***** cannot be cast to ******
> 	at ConditionEvaluator443abf2927ca4f64a4ad86407ae34799.evaluate(Unknown Source)
> 	at org.drools.rule.constraint.MvelConstraint.evaluate(MvelConstraint.java:200)
> 	at org.drools.rule.constraint.MvelConstraint.isAllowed(MvelConstraint.java:157)
> 	at org.drools.reteoo.FromNode.checkConstraintsAndPropagate(FromNode.java:318)
> 	at org.drools.reteoo.FromNode.assertLeftTuple(FromNode.java:164)
> 	at org.drools.reteoo.CompositeLeftTupleSinkAdapter.doPropagateAssertLeftTuple(CompositeLeftTupleSinkAdapter.java:232)
> 	at org.drools.reteoo.CompositeLeftTupleSinkAdapter.createAndPropagateAssertLeftTuple(CompositeLeftTupleSinkAdapter.java:116)
> 	at org.drools.reteoo.LeftInputAdapterNode.assertObject(LeftInputAdapterNode.java:154)
> 	at org.drools.reteoo.SingleObjectSinkAdapter.propagateAssertObject(SingleObjectSinkAdapter.java:59)
> Reason:
> ConditionEvaluator seems to be using lazy initializing and then caches generated class to evaluate this expression with another arguments.
> Given following:
> interface A {
>    String getString();
> }
> interface B {
>    String getString();
> }
> class X implements B, A {}
> class Y implements A{}
> rule "test rule"
> when:
>      A(string != null)
> then:
> end
> When rule engine is called for the first time with instance of class X, ConditionEvaluator will bind itself to first found interface implementing method getString(), i.e. interface B.
> Thus second call with instance of class Y will cause ClassCastException of casting Y to B.
> Solution: force MVEL to bind bytecode generated methods to class/interface declared in the rule explicitly, in our case - to interface A.
> Quickfix: use following declaration of class X:
> class X implements A, B {}
> Because ConditionEvaluator binds to first available interface, it will bind now to correct interface - to interface A.



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