Retrofit2 Handle condition when status code 200 but json structure different than datamodel class

Question

I\'m using Retrofit2 and RxJava2CallAdapterFactory.

The API I consume returns status code always as 200 and for success and response JSON string the JSON st

Answer 1

So you have two different successful (status code 200) responses from the same endpoint. One being the actual data model and one being an error (both as a json structure like this?:

Valid LoginBean response:

{
  "id": 1234,
  "something": "something"
}

Error response

{
  "error": "error message"
}

What you can do is have an entity that wraps both cases and use a custom deserializer.

class LoginBeanResponse {
  @Nullable private final LoginBean loginBean;
  @Nullable private final ErrorMessage errorMessage;

  LoginBeanResponse(@Nullable LoginBean loginBean, @Nullable ErrorMessage errorMessage) {
    this.loginBean = loginBean;
    this.errorMessage = errorMessage;
  }
  // Add getters and whatever you need
}

A wrapper for the error:

class ErrorMessage {
  String errorMessage;
  // And whatever else you need
  // ...
}

Then you need a JsonDeserializer:

public class LoginBeanResponseDeserializer implements JsonDeserializer {

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

    // Based on the structure you check if the data is valid or not
    // Example for the above defined structures:

    // Get JsonObject
    final JsonObject jsonObject = json.getAsJsonObject();
    if (jsonObject.has("error") {
      ErrorMessage errorMessage = new Gson().fromJson(jsonObject, ErrorMessage.class);
      return new LoginBeanResponse(null, errorMessage)
    } else {
      LoginBean loginBean = new Gson().fromJson(jsonObject, LoginBean.class):
      return new LoginBeanResponse(loginBean, null);
    }
  }
}

Then add this deserializer to the GsonConverterFactory:

GsonBuilder gsonBuilder = new GsonBuilder().registerTypeAdapter(LoginBeanResponse.class, new LoginBeanResponseDeserializer()).create():

apiClient = new Retrofit.Builder()
    .baseUrl(url)
    .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
    .addConverterFactory(GsonConverterFactory.create(gsonBuilder))
    .client(httpClient)
    .build();

This is the only way I can think of making this work. But as already mentioned this kind of API design is just wrong because status codes are there for a reason. I still hope this helps.

EDIT: What you can then do inside the class where you make the call to that Retrofit (if you already converted from Call to Single with RxJava) is actually return a proper error. Something like:

Single getLoginResponse(Map queryMap) {
    restApi.getLoginResponse(queryMap)
        .map(loginBeanResponse -> { if(loginBeanResponse.isError()) {
            Single.error(new Throwable(loginBeanResponse.getError().getErrorMessage()))
        } else { 
            Single.just(loginBeanReponse.getLoginBean()) 
        }})
}