String convertErrorAsJson(String errorMessage) {
    return ("{" + "\"cause\"" + ":" + "\"" + errorMessage + "\"" + "}");
  }
AbstractBaseController class contains common functionalities required for other controllers.

@since GemFire 8.0
geode-web-api/src/main/java/org/apache/geode/rest/internal/web/controllers/AbstractBaseController.java