Question

我有一个JSON对象，我想从中获取密钥名称并将它们存储在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;
}

如果我将此代码与简单的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，名称和消息（不是值）被添加到我的ArrayList中。一旦我尝试使用这个相同的代码与更复杂的JSON，如此

{"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;"
    }
}}

我只获得根密钥。有人能指出我正确的方向吗？

谢谢大家！

Answer 1

我没有使用Gson（JSON）API来处理循环和条件，而是更喜欢将Gson用于我认为最好的方法：只需几行代码即可提供非常简单的（de）序列化处理。我{（3）}来自（de）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，在序列化之前根据需要操纵数据，同样，在反序列化之后根据需要操作数据。

所以，如果由于某种原因我想要JSON结构中的所有键，并且我想使用Gson，我可能会按如下方式处理它。（当然，我现在无法想到为什么这样的事情会有用。）

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);
  }
}

<强> 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;"
        }
    }
}

<强> 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
        }]
    }
}]

使用Gson从JSON对象获取键名

1 个答案: