java - 如何定义类来使用 Gson 解析此 JSON？

Question

我得到一个像这样的 JSON 字符串:

{
  "cars": {
    "ford": {
      "length": 4460,
      "weight": 1450
    },
    "jeep": {
      "length": 4670,
      "weight": 1880
    },
    "toyota": {
      "length": 3830,
      "weight": 1120
    },
    .
    .
    .
    "audi": {
      "length": 5288,
      "weight": 2432
    },
    "subaru": {
      "length": 4755,
      "weight": 1790
    },
    "count": 128
  }
}

我尝试定义 java 类来使用 Gson 解析此 JSON。

public class CarSize {
    public int length;
    public int weight;
}

public class JSONData {
    public Map<String, CarSize> cars;
}

问题是cars不是纯 map ，它有 "count":128和128不是CarSize 。如何解析 JSON？

请注意，我无法修改 JSON 的源字符串。但我可以忽略“count”属性，因为我知道它的大小是 Map<String, CarSize> cars .

Answer 1

看起来您有 Cars带有汽车列表的对象 List<Car>和一个 count property .

问题是，count 属性位于 map 中。我所做的是扩展 map ，只是为了添加属性。然后，您需要为此映射定义自己的序列化器/反序列化器(来源get-nested-json-object-with-gson)

型号:

class Cars {
    private  MyMap cars = new MyMap();

    public MyMap getCars() {
        return cars;
    }
    public void setCars(MyMap cars) {
        this.cars = cars;
    }

    public void add(String name, Car car){
        cars.put(name, car);
        cars.setCount(cars.getCount()+1);
    }

}

class MyMap extends HashMap<String, Car> {
    private int count;

    public int getCount() {
        return count;
    }

    public void setCount(int count) {
        this.count = count;
    }
}

class Car {
    private int length;
    private int weight;

    public Car() {

    }

    public Car(int length, int weight) {
        this.length = length;
        this.weight = weight;
    }

    public int getLength() {
        return length;
    }

    public void setLength(int length) {
        this.length = length;
    }

    public int getWeight() {
        return weight;
    }

    public void setWeight(int weight) {
        this.weight = weight;
    }
}

自定义序列化器/解串器:

class MyDeserializer implements JsonDeserializer<MyMap>
{
    @Override
    public MyMap deserialize(JsonElement json, Type type, JsonDeserializationContext context) throws JsonParseException {
        JsonElement count = json.getAsJsonObject().remove("count");
        MyMap myMap = new Gson().fromJson(json.getAsJsonObject().toString(), type);
        if(count!=null){
            myMap.setCount(count.getAsInt());
        }
        return myMap;
    }
}

class MySerializer implements JsonSerializer<MyMap>
{
    @Override
    public JsonElement serialize(MyMap src, Type type, JsonSerializationContext context) {
        JsonElement serialize = context.serialize(src, Map.class);
        serialize.getAsJsonObject().add("count", new JsonPrimitive(src.getCount()));
        return serialize;
    }
}

读取和写入json的代码:

String json = "{\"cars\":{\"jeep\":{\"length\":4670,\"weight\":1450},\"ford\":{\"length\":4460,\"weight\":1880},\"count\":128}}";
Cars cars = new Cars();
cars.add("jeep", new Car(4670, 1450));
cars.add("ford", new Car(4460, 1880));

Gson gson = new GsonBuilder()
           .registerTypeAdapter(MyMap.class, new MyDeserializer())
           .registerTypeAdapter(MyMap.class, new MySerializer())
           .create();

String json2 = gson.toJson(cars);
cars = gson.fromJson(json, Cars.class);
cars = gson.fromJson(json2, Cars.class);