I'm no expert but recall there can be problems running "long running" (subjective) code from AWT's worker thread.
 
I thought it was good practice to run your "application code" in a worker thread. This was the first google hit I had on the matter. 
 
http://www.cs.helsinki.fi/u/vihavain/k03/Java/JavathreadsandGUI.html
 
Cheers,
 
Mike

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Edson Tirelli
Sent: 08 March 2008 13:15
To: Rules Users List
Subject: Re: [rules-users] Interesting null pointer exception when inserting afact.


   Jason,

   Can you please isolate and show us the rule that is creating the problem? It is happening either in a eval() statement or in a nested property access.

    []s
    Edson

2008/3/7, Jason Partyka <Jason.Partyka@hightowerinc.com>:
Hi,

This is in relation to drools 4.0.4

I have an interesting problem. I am getting a null pointer exception when I am inserting a fact into a StatefulSession object. What is odd about this NPE is that, as far as I can tell (and I have inserted a breakpoint right before I insert the fact) that all the properties in the object are initialized, and there are no rules accessing any thing that could be null.

So here's my exception trace (just first few lines to get context):

Exception in thread "AWT-EventQueue-0" org.drools.RuntimeDroolsException: java.lang.NullPointerException
  at org.drools.rule.EvalCondition.isAllowed(EvalCondition.java:76)
  at org.drools.reteoo.EvalConditionNode.assertTuple(EvalConditionNode.java:145)
  at org.drools.reteoo.SingleTupleSinkAdapter.createAndPropagateAssertTuple(SingleTupleSinkAdapter.java:55)
  at org.drools.reteoo.LeftInputAdapterNode.assertObject(LeftInputAdapterNode.java:116)
  at org.drools.reteoo.SingleObjectSinkAdapter.propagateAssertObject(SingleObjectSinkAdapter.java:22)
  at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:153)
  at org.drools.reteoo.Rete.assertObject(Rete.java:177)
  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:886)
  at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:858)
  at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:659)
  at com.hightower.drools.executablerules.Rules.setTemplate(Rules.java:112)
....
Caused by: java.lang.NullPointerException
  at org.drools.base.mvel.MVELEvalExpression.evaluate(MVELEvalExpression.java:39)
  at org.drools.rule.EvalCondition.isAllowed(EvalCondition.java:72)
  ... 39 more


(that setTemplate method is not a drools template)

Any ideas?

Thanks,
Jason

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  Edson Tirelli
  JBoss Drools Core Development
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