如何在Android上的Retrofit中处理可能是ARRAY或OBJECT的参数？

Question

我遇到的问题是我正在解析的API为大小为1的ARRAY返回一个OBJECT.

例如,有时API会响应:

{
    "monument": [
        {
            "key": 4152,
            "name": "MTS - Corporate Head Office",
            "categories": {},
            "address": {}
        },
        {
            "key": 4151,
            "name": "Canadian Transportation Agency",
            "categories": {},
            "address": {}
        },
        {
            "key": 4153,
            "name": "Bank of Montreal Building",
            "categories": {},
            "address": {}
        }
    ],
}

但是,如果monument数组只有一个项目,它就变成了一个OBJECT(注意缺少[]括号),如下所示:

{
    "monument": {
        "key": 4152,
        "name": "MTS - Corporate Head Office",
        "categories": {},
        "address": {}
    }
}

如果我像这样定义我的模型,只返回一个项目时会出错:

public class Locations {
    public List<Monument> monument;
}

如果只返回一个项目,我会收到以下错误:

Expected BEGIN_OBJECT but was BEGIN_ARRAY ...

如果我像这样定义我的模型:

public class Locations {
    public Monument monument;
}

并且API返回ARRAY我得到了相反的错误

Expected BEGIN_ARRAY  but was BEGIN_OBJECT ...

我无法在模型中定义多个具有相同名称的项目.我该如何处理这个案子？

注意:我无法对API进行更改.

Answer 1

诀窍是为你的班级编写自己的Gson反序列化器Locations.这将检查纪念碑元素是对象还是数组.像这样:

public class LocationsDeserializer implements JsonDeserializer<Locations> {

    @Override
    public Locations deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {

        JsonElement monumentElement = json.getAsJsonObject().get("monument");
        if (monumentElement.isJsonArray()) {
            return new Locations((Monument[]) context.deserialize(monumentElement.getAsJsonArray(), Monument[].class));
        } else if (monumentElement.isJsonObject()) {
            return new Locations((Monument) context.deserialize(monumentElement.getAsJsonObject(), Monument.class));
        } else {
            throw new JsonParseException("Unsupported type of monument element");
        }
    }
}

为方便起见,在您的Locations类中添加一个vararg构造函数:

public class Locations {
    public List<Monument> monuments;

    public Locations(Monument ... ms) {
        monuments = Arrays.asList(ms);
    }
}

你的纪念碑课程保持不变.就像是:

public class Monument {
    public int key;
    public String name;
    // public Categories categories;
    // public Address address;
}

最后,创建自己的Gson对象并将其传递给改造RestAdapter.

Gson gson = new GsonBuilder().registerTypeAdapter(Locations.class, new LocationsDeserializer()).create();

RestAdapter restAdapter = new RestAdapter.Builder()
            .setEndpoint(baseUrl)
            .setConverter(new GsonConverter(gson))
            .build();

Answer 2

作为我之前的答案的补充,这是一个使用a的解决方案TypeAdapter.

public class LocationsTypeAdapter extends TypeAdapter<Locations> {

    private Gson gson = new Gson();

    @Override
    public void write(JsonWriter jsonWriter, Locations locations) throws IOException {
        gson.toJson(locations, Locations.class, jsonWriter);
    }

    @Override
    public Locations read(JsonReader jsonReader) throws IOException {
        Locations locations;

        jsonReader.beginObject();
        jsonReader.nextName();       

        if (jsonReader.peek() == JsonToken.BEGIN_ARRAY) {
            locations = new Locations((Monument[]) gson.fromJson(jsonReader, Monument[].class));
        } else if(jsonReader.peek() == JsonToken.BEGIN_OBJECT) {
            locations = new Locations((Monument) gson.fromJson(jsonReader, Monument.class));
        } else {
            throw new JsonParseException("Unexpected token " + jsonReader.peek());
        }

        jsonReader.endObject();
        return locations;
    }
}