java - 解析 json 数组内的 json 数组时遇到问题

Question

我在解析 java 中的简单 json 时遇到问题。这是示例 json。

[
  {
    "politics": [
      {
        "type": "admin2",
        "friendly_type": "country",
        "name": "United States",
        "code": "usa"
      },
      {
        "type": "admin6",
        "friendly_type": "county",
        "name": "Gratiot",
        "code": "26_057"
      },
      {
        "type": "constituency",
        "friendly_type": "constituency",
        "name": "Eighth district, MI",
        "code": "26_08"
      },
      {
        "type": "admin6",
        "friendly_type": "county",
        "name": "Clinton",
        "code": "26_037"
      },
      {
        "type": "admin4",
        "friendly_type": "state",
        "name": "Michigan",
        "code": "us26"
      },
      {
        "type": "constituency",
        "friendly_type": "constituency",
        "name": "Fourth district, MI",
        "code": "26_04"
      }
    ],
    "location": {
      "latitude": 43.111976,
      "longitude": -84.71275
    }
  }
]

现在这给了我正确的 json 索引。

JSONParser parser = new JSONParser();
Object obj = parser.parse(output);
JSONArray array = (JSONArray)obj;
String jsonobj = array.get(0).toString();

{"politics":[{"code":"usa","name":"United States","type":"admin2","friendly_type":"country"},{"code":"26_057","name":"Gratiot","type":"admin6","friendly_type":"county"},{"code":"26_08","name":"Eighth district, MI","type":"constituency","friendly_type":"constituency"},{"code":"26_037","name":"Clinton","type":"admin6","friendly_type":"county"},{"code":"us26","name":"Michigan","type":"admin4","friendly_type":"state"},{"code":"26_04","name":"Fourth district, MI","type":"constituency","friendly_type":"constituency"}],"location":{"latitude":43.111976,"longitude":-84.71275}}

但我似乎无法从中获得我想要的属性。

JSONObject obj1 = new JSONObject(jsonobj);
String n = obj1.getString("admin4");
System.out.println(n);

我从这个 json 中需要的只是密歇根州。我哪里错了？非常感谢您的帮助。

Answer 1

首先，array.get(0) 将从主数组中获取第一个元素。第一个元素是一个 JSON 对象，具有两个属性 politics 和 location。您似乎对 politics 属性的数组值内的值感兴趣。您必须使用此 ((JSONArray)((JSONObject)array.get(0)).get("politics")) 来获取该数组。

其次，admin4 不是一个属性，它实际上是 type 属性的值。您必须循环遍历数组才能找到它。

这是一个完整的示例:

JSONParser parser = new JSONParser();
Object obj = parser.parse(output);
JSONArray array = (JSONArray)obj;
JSONArray politics = ((JSONObject)array.get(0)).get("politics"));
JSONObject obj = null;
for(int i = 0; i < politics.size(); i++){
    if(((JSONObject)politics.get(i)).getString("type").equals("admin4")){
        obj = ((JSONObject)politics.get(i));
    }
}
if(obj != null){
    // Do something with the object.
}

您似乎正在使用simple json 库。我不记得它是 .get("politics") 还是 .getJSONObject("politics")。我的示例中的方法名称可能还有其他错误。