Custom extension elements are a standardized way to extend the BPMN model.The Camunda extension elements are fully implemented in the BPMN model API, but unknown extension elements can also easily be accessed and added.

    Every BPMN BaseElement can have a child element of the type extensionElements.This element can contain all sorts of extension elements. To access theextension elements you have to call the getExtensionElements() method and,if no such child element exists, you must create one first.

    1. StartEvent startEvent = modelInstance.newInstance(StartEvent.class);
    2. ExtensionElements extensionElements = startEvent.getExtensionElements();
    3. if (extensionElements == null) {
    4.   extensionElements = modelInstance.newInstance(ExtensionElements.class);
    5.   startEvent.setExtensionElements(extensionElements);
    6. }
    7. Collection<ModelElementInstance> elements = extensionElements.getElements();

    After that you can add or remove extension elements to the collection.

    1. CamundaFormData formData = modelInstance.newInstance(CamundaFormData.class);
    2. extensionElements.getElements().add(formData);
    3. extensionElements.getElements().remove(formData);

    You can also access a query-like interface to filter the extension elements.

    1. extensionElements.getElementsQuery().count();
    2. extensionElements.getElementsQuery().list();
    3. extensionElements.getElementsQuery().singleResult();
    4. extensionElements.getElementsQuery().filterByType(CamundaFormData.class).singleResult();

    Additionally, there are some shortcuts to add new extension elements. You can usethe namespaceUri and the elementName to add your own extension elements. Oryou can use the class of a known extension element type, e.g., the camundaextension elements. The extension element is added to the BPMN element and returnedso that you can set attributes or add child elements.

    1. ModelElementInstance element = extensionElements.addExtensionElement("http://example.com/bpmn", "myExtensionElement");
    2. CamundaExecutionListener listener = extensionElements.addExtensionElement(CamundaExecutionListener.class);

    Another helper method exists for the fluent builder API which allows you to add prior defined extension elements.

    1. CamundaExecutionListener camundaExecutionListener = modelInstance.newInstance(CamundaExecutionListener.class);
    2. camundaExecutionListener.setCamundaClass("org.camunda.bpm.MyJavaDelegte");
    3. startEvent.builder()
    4.   .addExtensionElement(camundaExecutionListener);

    原文: https://docs.camunda.org/manual/7.9/user-guide/model-api/bpmn-model-api/extension-elements/