URI: platform:/resource/BPMNtest/new_file.bpmn2, cause: 
java.lang.IllegalStateException: Cannot modify resource set without a write transaction
	at org.eclipse.emf.transaction.impl.TransactionChangeRecorder.assertWriting(TransactionChangeRecorder.java:348)
	at org.eclipse.emf.transaction.impl.TransactionChangeRecorder.appendNotification(TransactionChangeRecorder.java:302)
	at org.eclipse.emf.transaction.impl.TransactionChangeRecorder.processObjectNotification(TransactionChangeRecorder.java:284)
	at org.eclipse.emf.transaction.impl.TransactionChangeRecorder.notifyChanged(TransactionChangeRecorder.java:240)
...

final BpmnDiagramEditor editor = (BpmnDiagramEditor) Util
	.getActiveEditor();
TransactionalEditingDomain domain = editor.getEditingDomain();
ResourceSet set = domain.getResourceSet();
set.getResourceFactoryRegistry().getExtensionToFactoryMap()
	.put("wsdl", new WSDLResourceFactoryImpl());
Resource r = null;

r = set.createResource(URI.createURI(page.getFilePath()
	.replaceAll("\\\\", "/")
	.replace(Platform.getLocation().toString(), "")));

try {
	r.load(Collections.EMPTY_MAP);
} catch (IOException e) {
	return false;
}

r.setModified(false);
editor.getImportUtil().addResource(r, Util.PORTTYPES);
final List<EObject> objs = editor.getImportUtil()
	.getObjectsForResource(r);

Definitions def = null;
for (Resource res : set.getResources()) {
	if (res.getURI().fileExtension().equals("bpmn2")) {
		def = ((DocumentRoot) res.getContents().get(0))
			.getDefinitions();
		break;
	}
}

final Definitions finalDef = def;
domain.getCommandStack().execute(new RecordingCommand(domain) {
			
@Override
protected void doExecute() {
	for (EObject eObject : objs) {
		Interface iface = Bpmn2Factory.eINSTANCE.createInterface();
		iface.setId(EcoreUtil.generateUUID());
		iface.setImplementationRef(eObject);
		for (Operation op : (EList<Operation>) ((PortType) eObject)
				.getEOperations()) {
			org.eclipse.bpmn2.Operation newOp = Bpmn2Factory.eINSTANCE
					.createOperation();
			newOp.setImplementationRef(op);
			iface.getOperations().add(newOp);
		}
		finalDef.getRootElements().add(iface);
	}
}
});