[rules-users] Unable to create Field Extractor

[Djerir Smail]

Hello everybody,

*I need help please  **I am new in drools,  to start I am trying to 
write some simple examples with drools fusion . I wrote a rule  which 
print a message when an alarm is received multiple times during 20 
minutes but i get this error 
*
     [java] Unable to create Field Extractor for 'BtsNumber' of 
'[ClassObjectType event=com.mfe.casestudy.pojo.AlarmFailureEvent]' in 
rule 'MaxBtsAlarmrule' : [Rule name='MaxBtsAlarmrule']
     [java] java.lang.IllegalArgumentException: Could not parse knowledge.
     [java]     at 
com.mfe.casestudy.test.Tester.prepareKnowledgeBase(Tester.java:73)
     [java]     at com.mfe.casestudy.test.Tester.setUp(Tester.java:43)
     [java]     at com.mfe.casestudy.test.Tester.main(Tester.java:87)
     [java] Exception in thread "main" java.lang.NullPointerException
     [java]     at 
com.mfe.casestudy.test.Tester.prepareStatefulKnowledgeSession(Tester.java:58)
     [java]     at com.mfe.casestudy.test.Tester.setUp(Tester.java:44)
     [java]     at com.mfe.casestudy.test.Tester.main(Tester.java:87)
     [java] Java Result: 1
main:


*This is my rule  it calculates  the number of alarms received from one  
BTS and if this number  exceeds the threshold it prints a warning message *
rule "MaxBtsAlarmrule"
dialect "mvel"
no-loop true
salience 100
when
    $BTS : BTS()
   
    # check if the number of alarms of last 20 minutes exceeds
    # the BTS threshold
    $numOfAlarms : Number( intValue > $BTS.threshold )
    from accumulate(
        AlarmFailureEvent(
            BtsNumber == $BTS.number,
            $ID : ID
        )
        over window:time(3) from
        entry-point BTSAlarmStream,
        count($ID)
    )
   

then
  System.out.println("BTS should  be restarted...");
   
end

Finally this is the  alarm event class

public class AlarmFailureEvent implements Serializable {
   
    /**
     *
     */
    private static final long serialVersionUID = 1L;
   
    public String BtsNumber = "";
    private int code = 0;
    private int ID=0;
    public  AlarmFailureEvent(String BtsNumber, int code ,int ID) {
        this.BtsNumber = BtsNumber;
        this.ID=ID;
        this.code=code;
    }
   
    public void setID(int iD) {
        this.ID = iD;
    }
    public int getID() {
        return this.ID;
    }
    public void setCode(int code) {
        this.code = code;
    }
    public int getCode() {
        return this.code;
    }

    public void setBtsNumber(String btsNumber) {
        this.BtsNumber = btsNumber;
    }

    public String getBtsNumber() {
        return BtsNumber;
    }
   
}

*Thank you *