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

Thursday, 11 July 2013

     [
https://issues.jboss.org/browse/DROOLS-185?page=com.atlassian.jira.plugin...
]

Mario Fusco resolved DROOLS-185.
--------------------------------

    Resolution: Cannot Reproduce Bug

I tried the test case that follows on the master branch and couldn't reproduce any
problem so I am assuming that it has been already fixed (provided that I am not missing
something), please advice.

{code}
    @Test
    public void testCCE() {
        String str =
                "import org.drools.compiler.integrationtests.MiscTest2.*\n" +
                "\n" +
                "rule \"test rule\"\n" +
                "when\n" +
                "     $i : I1(string == null)\n" +
                "then\n" +
                "    System.out.println($i.getClass());" +
                "end\n";

        KnowledgeBase kbase = loadKnowledgeBaseFromString(str);
        StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();

        ksession.insert(new X());
        ksession.fireAllRules();

        ksession.insert(new Y());
        ksession.fireAllRules();
    }

    public interface I1 { String getString(); }
    public interface I2 { String getString(); }
    public static class X implements I2, I1 {
        public String getString() {
            return null;
        }
    }
    public static class Y implements I1{
        public String getString() {
            return null;
        }
    }
{code}

...
 ClassCastException at ConditionEvaluator
 ----------------------------------------

                 Key: DROOLS-185
                 URL: https://issues.jboss.org/browse/DROOLS-185
             Project: Drools
          Issue Type: Bug
      Security Level: Public(Everyone can see) 
    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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