如何使用 java 从复杂的 JSON 中获取数据

Question

我是 android 应用程序开发的新手，我很震惊，因为我无法从 JSON 获取我需要的特定数据。

这是 JSON 文件。

{
  "message": "",
  "cod": "200",
  "city_id": 4887398,
  "calctime": 0.0863,
  "cnt": 4,
  "list": [
    {
      "main": {
        "temp": 268.987,
        "temp_min": 268.987,
        "temp_max": 268.987,
        "pressure": 1001.11,
        "sea_level": 1024.68,
        "grnd_level": 1001.11,
        "humidity": 100
      },
      "wind": {
        "speed": 5.06,
        "deg": 291.002
      },
      "clouds": {
        "all": 48
      },
      "weather": [
        {
          "id": 802,
          "main": "Clouds",
          "description": "scattered clouds",
          "icon": "03d"
        }
      ],
      "dt": 1485703465
    },
    {
      "main": {
        "temp": 268.097,
        "temp_min": 268.097,
        "temp_max": 268.097,
        "pressure": 1003.57,
        "sea_level": 1027.08,
        "grnd_level": 1003.57,
        "humidity": 100
      },
      "wind": {
        "speed": 8.56,
        "deg": 314.007
      },
      "clouds": {
        "all": 44
      },
      "weather": [
        {
          "id": 802,
          "main": "Clouds",
          "description": "scattered clouds",
          "icon": "03d"
        }
      ],
      "dt": 1485730032
    },
    {
      "main": {
        "temp": 266.787,
        "temp_min": 266.787,
        "temp_max": 266.787,
        "pressure": 1005.73,
        "sea_level": 1029.63,
        "grnd_level": 1005.73,
        "humidity": 100
      },
      "wind": {
        "speed": 6.79,
        "deg": 316.012
      },
      "clouds": {
        "all": 0
      },
      "weather": [
        {
          "id": 800,
          "main": "Clear",
          "description": "Sky is Clear",
          "icon": "01n"
        }
      ],
      "dt": 1485755383
    },
    {
      "main": {
        "temp": 263.64,
        "pressure": 1015,
        "humidity": 57,
        "temp_min": 262.15,
        "temp_max": 265.15
      },
      "wind": {
        "speed": 2.6,
        "deg": 280
      },
      "clouds": {
        "all": 1
      },
      "weather": [
        {
          "id": 800,
          "main": "Clear",
          "description": "sky is clear",
          "icon": "01n"
        }
      ],
      "dt": 1485780512
    }
  ]
}

我要获取的是主要和天气 object 的所有值的描述，例如我试图在我的屏幕上打印它。如何循环以获得这个结果？

          "main": "Clouds",
          "description": "scattered clouds",
          "main": "Clouds",
          "description": "scattered clouds",
          "main": "Clear",
          "description": "Sky is Clear",
          "main": "Clear",
          "description": "Sky is Clear",

谢谢你

Answer 1

您可以使用 Jackson 来实现它。

对于您的应用，您需要这些库：

• Jackson 数据绑定： https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-datad/2.1

• Jackson 内核： https://mvnrepository.com/artifact/com.fasterxml.ZB41779690B83F182ACC67D6388C7BAC911Z.core/jackson-core.2/

public static void main(String[] args) throws JsonProcessingException {

    String json = "your json as string";

    JsonNode root = (new ObjectMapper()).readTree(json); //JsonProcessingException

    //check if root has node list
    if(root.has("list")){

        //get node list from root
        JsonNode list = root.get("list");

        //check if list is an array node
        if(list.isArray()){

            //iterate list
            for(JsonNode listElem : list){

                //check if current node fromt list has node weather
                if(listElem.has("weather")){

                    //get node weather
                    JsonNode weather = listElem.get("weather");

                    //check if weather is array
                    if(weather.isArray()){

                        for(JsonNode weatherElem : weather){

                            if(weatherElem.has("main") && weatherElem.has("description")){

                                System.out.println(weatherElem.get("main") + " - " + weatherElem.get("description"));

                            }

                        }

                    }

                }

            }

        }

    }

}

但是，如果您确定 json 结构始终相同。 您可以跳过所有检查。

public static void main(String[] args) throws JsonProcessingException {

    String json = "your json as string";

    JsonNode root = (new ObjectMapper()).readTree(json); //JsonProcessingException

    for(JsonNode listElem : root.get("list")){

        for(JsonNode weatherElem : listElem.get("weather")) {

            System.out.println(weatherElem.get("main") + " - " + weatherElem.get("description"));

        }

    }

}