JBoss Community

I am implement Log Event Listener using example given in user guide

<process name="EventListener" xmlns="http://jbpm.org/4.4/jpdl">

  <on event="start">
    <event-listener class="org.jbpm.examples.eventlistener.LogListener">
      <field name="msg"><string value="start on process definition"/></field>
    </event-listener>
  </on>

  <start>
    <transition to="wait"/>
  </start>

  <state name="wait">
    <on event="start">
      <event-listener class="org.jbpm.examples.eventlistener.LogListener">
        <field name="msg"><string value="start on activity wait"/></field>
      </event-listener>
    </on>
    <on event="end">
      <event-listener class="org.jbpm.examples.eventlistener.LogListener">
        <field name="msg"><string value="end on activity wait"/></field>
      </event-listener>
    </on>
    <transition to="park">
      <event-listener class="org.jbpm.examples.eventlistener.LogListener">
        <field name="msg"><string value="take transition"/></field>
      </event-listener>
    </transition>
  </state>

  <state name="park"/>

</process>




and LogListener class like below 


public class LogListener implements EventListener {

  // value gets injected from process definition
  String msg;

  public void notify(EventListenerExecution execution) {
    List<String> logs = (List<String>) execution.getVariable("logs");
    if (logs==null) {
      logs = new ArrayList<String>();
      execution.setVariable("logs", logs);
    }

    logs.add(msg);

    execution.setVariable("logs", logs);
  }
}



but when I am testing using Junit 


ProcessInstance processInstance = executionService.startProcessInstanceByKey("EventListener");

In above line getting Nullpointer Exception?

can any one help regards this , or any other reference to implement Event Listener in jbpm4

Thanks all