json数据：{
 "devices": {
   "cameras": {
    "device_id": "awJo6rH",
     "last_event": {
       "has_sound": true,
       "has_motion": true,
       "has_person": true,
       "start_time": "2016-12-29T00:00:00.000Z",
        "end_time": "2016-12-29T18:42:00.000Z"
      }
    }
  }

解析json
   val jsonObject = JSON.parseObject(json)
      val lastEvent = jsonObject.getJSONObject("devices")
        .getJSONObject("cameras")
        .getJSONObject("last_event")
      val hasPerson = lastEvent.getString("has_person")
      val startTime = lastEvent.getString("start_time")
      (startTime,hasPerson)
    }).toDF("startTime","hasPerson")