I wish to have a rule that says, if I get one event, but not another one
after a period, then do something.
But I also want to only do this once..
So, I wrote the rules: (using the eclipse sample project)
declare Message
@role( event )
end
rule "Hello World"
when
$m : Message( status == Message.HELLO )
not ( Message( status== Message.GOODBYE, this after [0s,1m]
$m)) ;
then
System.out.println( "Hello" );
end
rule "GoodBye"
when
$one : Message( status == Message.HELLO )
$two : Message( status == Message.HELLO )
then
System.out.println( "Two hellos, remove one" );
retract($two);
end
But, when I run;
Message message = new Message();
message.setMessage("Hello World");
message.setStatus(Message.HELLO);
ksession.insert(message);
Message message2 = new Message();
message2.setMessage("Hello World");
message2.setStatus(Message.HELLO);
ksession.insert(message2);
ksession.fireAllRules();
I get:
Two hellos, remove one
java.lang.NullPointerException
at
org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:970)
at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:885)
at org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1086)
at
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:660)
at
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:627)
at
org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:183)
at com.sample.DroolsTest.main(DroolsTest.java:38)
What am i doing wrong?
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