[jboss-jira] [JBoss JIRA] (DROOLS-185) ClassCastException at ConditionEvaluator
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https://issues.jboss.org/browse/DROOLS-185?page=com.atlassian.jira.plugin...
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Davide Sottara commented on DROOLS-185:
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This issue is very general and can manifest in a variety of cases. Drools should obey the
laws of Java when it comes to implicit casting.
Notice that, for example, in Java Long and Integer are incompatible classes (unlike the
primitives long and int) and Drools should not change that.
If you have reproducers where the java conventions are violated, please post them. It is
unlikely that they will be fixed in 5.6, but newer
versions will provide the correct behavior.
Thanks
Davide
explicit casts / transformations / wrappings / changes in the data models are usually
required workarounds
ClassCastException at ConditionEvaluator
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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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