code: private String encodeRecord (String record)throws  IOException {
      // Convert original json object to a new json object with format {"Body": "originalJson"}
      // Add new json object to an array and send the whole array to eventhub using REST api
      // Refer to https://docs.microsoft.com/en-us/rest/api/eventhub/send-batch-events
      ArrayList<EventhubRequest> arrayList = new ArrayList<>();
      arrayList.add(new EventhubRequest(record));
  
      return mapper.writeValueAsString (arrayList);
    }
docs: A single record is wrapped by a 'Body' json object
  encode this json object