Struggling with a design issue using Gson as my parsing library while creating a library to consume a Json API.
One of the endpoints returns an array of objects under normal circumstances:
[
{
"name": "John",
"age" : 21
},
{
"name": "Sarah",
"age" : 32
}
]
However, the error schema for all API endpoints is a json object instead of an array.
{
"errors": [
{
"code": 1001,
"message": "Something blew up"
}
]
}
The challenge arises when representing this in POJOs. To handle this, I created an abstract ApiResponse class solely for mapping errors attribute:
public abstract class ApiResponse{
@SerializedName("errors")
List<ApiResponseError> errors;
}
public class ApiResponseError {
@SerializedName("code")
public Integer code;
@SerializedName("message")
public String message;
}
To automate error mapping and create a specific POJO for each endpoint response, I wanted to inherit from ApiResponse. However, since the top level object in the response is an array (when successful), I had to find a workaround.
I proceeded by extending ApiResponse:
public class ApiResponsePerson extends ApiResponse {
List<Person> persons;
}
And implemented a custom deserializer to parse the json correctly based on the type of the top level object:
public class DeserializerApiResponsePerson implements JsonDeserializer<ApiResponsePerson> {
@Override
public ApiResponse deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
ApiResponsePerson response = new ApiResponsePerson();
if (json.isJsonArray()) {
Type personType = new TypeToken<List<Person>>() {}.getType();
response.persons = context.deserialize(json, personType);
return response;
}
if (json.isJsonObject()) {
JsonElement errorJson = json.getAsJsonObject().get("errors");
Type errorsType = new TypeToken<List<ApiResponseError>>() {}.getType();
response.errors = context.deserialize(errorJson, errorsType);
return response;
}
throw new JsonParseException("Unexpected Json for 'ApiResponse'");
}
}
This custom deserializer will be added to the Gson instance:
Gson gson = new GsonBuilder()
.registerTypeAdapter(ApiResponsePerson.class, new DeserializerApiResponsePerson())
.create();
Is there a more efficient way to accomplish this without manual intervention? Any better suggestions or possible failure scenarios I may have overlooked?
Thank you.