java - 使用 Gson 从 JSON 对象获取键名

Question

我有一个 JSON 对象，我想从中获取键名并将它们存储在 ArrayList 中。我使用了以下代码

jsonData(String filename) {
    JsonParser parser = new JsonParser();
    JsonElement jsonElement = null;

    try {
        jsonElement = parser.parse(new FileReader(filename));
    } catch (JsonIOException | JsonSyntaxException | FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    JsonObject jsonObject = jsonElement.getAsJsonObject();

    int i = 0;
    for (Entry<String, JsonElement> entry : jsonObject.entrySet()) {
        String key = entry.getKey();
        JsonElement value = entry.getValue();

        keys.add(key);
        i++;
    }
    nKeys = i;
}

如果我将这段代码与一个简单的 JSON 对象一起使用

{
    "age":100,
    "name":"mkyong.com",
    "messages":["msg 1","msg 2","msg 3"]
}

这很好用。年龄、姓名和消息(不是值)被添加到我的 ArrayList。一旦我尝试将相同的代码与更复杂的 JSON 一起使用，就像这样

{"widget": {
    "debug": "on",
    "window": {
        "title": "Sample Konfabulator Widget",
        "name": "main_window",
        "width": 500,
        "height": 500
    },
    "image": { 
        "src": "Images/Sun.png",
        "name": "sun1",
        "hOffset": 250,
        "vOffset": 250,
        "alignment": "center"
    },
    "text": {
        "data": "Click Here",
        "size": 36,
        "style": "bold",
        "name": "text1",
        "hOffset": 250,
        "vOffset": 100,
        "alignment": "center",
        "onMouseUp": "sun1.opacity = (sun1.opacity / 100) * 90;"
    }
}}

我只得到根 key 。有人可以为此指出正确的方向吗？

谢谢大家!

Answer 1

与其使用循环和条件遍历 Gson (JSON) API，我更愿意将 Gson 用于我认为它最擅长的方面:只需几行代码即可提供非常简单的(反)序列化处理。我会 decouple来自(反)序列化问题的任何数据操作/查询/表示问题。换句话说，尽可能合理地在序列化之前根据需要操作数据，同样地，在反序列化之后根据需要操作数据。

因此，如果出于某种原因我想要来自 JSON 结构的所有键，并且我想使用 Gson，我可能会按如下方式处理它。 (当然，我目前想不出这样的东西有什么用处。)

import java.io.FileReader;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Map;

import com.google.gson.Gson;

public class App
{
  public static void main(String[] args) throws Exception
  {
    List keys1 = getKeysFromJson("input_without_lists.json");
    System.out.println(keys1.size());
    System.out.println(keys1);

    List keys2 = getKeysFromJson("input_with_lists.json");
    System.out.println(keys2.size());
    System.out.println(keys2);
  }

  static List getKeysFromJson(String fileName) throws Exception
  {
    Object things = new Gson().fromJson(new FileReader(fileName), Object.class);
    List keys = new ArrayList();
    collectAllTheKeys(keys, things);
    return keys;
  }

  static void collectAllTheKeys(List keys, Object o)
  {
    Collection values = null;
    if (o instanceof Map)
    {
      Map map = (Map) o;
      keys.addAll(map.keySet()); // collect keys at current level in hierarchy
      values = map.values();
    }
    else if (o instanceof Collection)
      values = (Collection) o;
    else // nothing further to collect keys from
      return;

    for (Object value : values)
      collectAllTheKeys(keys, value);
  }
}

input_without_lists.json

{
    "widget": {
        "debug": "on",
        "window": {
            "title": "Sample Konfabulator Widget",
            "name": "main_window",
            "width": 500,
            "height": 500
        },
        "image": {
            "src": "Images/Sun.png",
            "name": "sun1",
            "hOffset": 250,
            "vOffset": 250,
            "alignment": "center"
        },
        "text": {
            "data": "Click Here",
            "size": 36,
            "style": "bold",
            "name": "text1",
            "hOffset": 250,
            "vOffset": 100,
            "alignment": "center",
            "onMouseUp": "sun1.opacity = (sun1.opacity / 100) * 90;"
        }
    }
}

input_with_lists.json

[{
    "widget": {
        "debug": "on",
        "windows": [{
            "title": "Sample Konfabulator Widget",
            "name": "main_window",
            "width": 500,
            "height": 500
        },{
            "title": "Sample Konfabulator Widget",
            "name": "main_window",
            "width": 500,
            "height": 500
        },{
            "title": "Sample Konfabulator Widget",
            "name": "main_window",
            "width": 500,
            "height": 500
        }]
    }
}]