In my example:

package com.sample;

import org.jbpm.graph.def.ProcessDefinition;
import org.jbpm.graph.exe.ProcessInstance;
import org.jbpm.graph.exe.Token;
import org.jbpm.taskmgmt.exe.TaskInstance;
import junit.framework.TestCase;

public class BlowsUp {
 public void testTransitionAction() {
 ProcessDefinition processDefinition = ProcessDefinition.parseXmlResource("simple.par/processdefinition.xml");

 ProcessInstance processInstance = new ProcessInstance(processDefinition);

 processInstance.signal();

 processInstance.signal();

 }
 public static void main(String[] args){
 BlowsUp bu = new BlowsUp();
 bu.testTransitionAction();
 }
}

I get this error.

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/commons/logging/LogFactory
 at org.jbpm.graph.def.GraphElement.<clinit>(GraphElement.java:384)
 at com.sample.BlowsUp.testTransitionAction(BlowsUp.java:11)
 at com.sample.BlowsUp.main(BlowsUp.java:38)

I suppose that i've to do something in a xml file. I don't know what. Can anybody help me?

Thanks.