Association association = (Association) artifact;
String sourceRef = association.getSourceRef();
String targetRef = association.getTargetRef();
// source and target can be instance of FlowElement or Artifact
BaseElement sourceElement = bpmnModel.getFlowElement(sourceRef);
BaseElement targetElement = bpmnModel.getFlowElement(targetRef);
if (sourceElement == null) {
sourceElement = bpmnModel.getArtifact(sourceRef);
}
if (targetElement == null) {
targetElement = bpmnModel.getArtifact(targetRef);