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Using Retrofit and RxJava, how do I deserialize JSON when it doesn't map directly to a model object?

The API I'm working with returns objects (and their containing objects) in a "flat" format and I'm having trouble getting this to work elegantly with Retrofit and RxJava.
Consider this JSON response for an /employees/{id} endpoint:
{
"id": "123",
"id_to_name": {
"123" : "John Doe"
},
"id_to_age": {
"123" : 30
}
}
Using Retrofit and RxJava, how do I deserialize this to a Employee object with fields for name and age?
Ideally I'd like RxJava's onNext method to be called with an Employee object. Is this possible? Could this perhaps be done with some type of custom deserializer subclass (I'm using Gson at the moment)?
I realize I could create an EmployeeResponse object that maps directly to the JSON response, but having to map the EmployeeResponse to the Employee object every time I use this in an activity seems kind of unfortunate. It also gets much more complicated when the flat response also contains other objects that need to get deserialized and set as fields on the Employee.
Is there a better way?

The complete solution to this will seem like a lot, but this will let you write Retrofit interfaces with Employee instead of EmployeeResponse. Here's the game plan:
You will still need both EmployeeResponse and Employee objects, where EmployeeResponse just maps exactly to what you'd get from the API. Treat the response as a builder for Employee and write a static factory method that returns an Employee from an EmployeeResponse, ie. Employee employee = Employee.newInstance(response);
You will be creating a custom TypeAdapterFactory for Gson. When Gson sees you request a Employee object, we will have the TypeAdapter actually create an EmployeeResponse, then return the Employee via the static factory method described above.
Your TypeAdapterFactory will look something like this:
public class EmployeeAdapterFactory implements TypeAdapterFactory {
#Override public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
return type.getRawType() == Employee.class
? (TypeAdapter<T>) employeeAdapter(gson, (TypeToken<Employee>) type)
: null;
}
private TypeAdapter<Employee> employeeAdapter(Gson gson, TypeToken<Employee> type) {
return new TypeAdapter<Employee>() {
#Override public void write(JsonWriter out, Employee value) throws IOException {
// TODO serialization logic to go from an Employee back to EmployeeResponse structure, if necessary
}
#Override public Employee read(JsonReader in) throws IOException {
return Employee.newInstance(gson.fromJson(in, EmployeeResponse.class));
}
};
}
}
Register the factory when you make Gson:
Gson gson = new GsonBuilder()
.registerTypeAdapterFactory(new EmployeeAdapterFactory())
.build();
Retrofit retrofit = new Retrofit.Builder().baseUrl("https://foo.bar")
.addConverterFactory(GsonConverterFactory.create(gson))
... // your other Retrofit configs, like RxJava call adapter factory
.build();
And now you can safely define all your Retrofit interfaces with Employee instead of EmployeeResponse.

How to get response as String using retrofit without using GSON or any other library in android [duplicate]

This question already has answers here:
Unable to create call adapter for class example.Simple
(19 answers)
Closed 7 years ago.
I am trying to get response from the following Api :
https://api.github.com/users/username
But I don't know how to get response as String so that I can use the String to parse and get the JSONObject.
Retrofit version used:
retrofit:2.0.0-beta1
I have tried this until now:
public interface GitHubService {
#GET("/users/{user}")
public String listRepos(#Path("user") String user,Callback<String> callback);
}
retrieving :
GitHubService service = retrofit.create(GitHubService.class);
service.listRepos("username", new Callback<String>() {
#Override
public void onResponse(Response response) {
System.out.println(response.toString());
}
#Override
public void onFailure(Throwable t) {
}
});
exception:
Caused by: java.lang.IllegalArgumentException: Could not locate call adapter for class java.lang.String. Tried:
* retrofit.ExecutorCallAdapterFactory
at retrofit.Utils.resolveCallAdapter(Utils.java:67)
at retrofit.MethodHandler.createCallAdapter(MethodHandler.java:49)
Any help would be really appreciated.

** Update ** A scalars converter has been added to retrofit that allows for a String response with less ceremony than my original answer below.
Example interface --
public interface GitHubService {
#GET("/users/{user}")
Call<String> listRepos(#Path("user") String user);
}
Add the ScalarsConverterFactory to your retrofit builder. Note: If using ScalarsConverterFactory and another factory, add the scalars factory first.
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(BASE_URL)
.addConverterFactory(ScalarsConverterFactory.create())
// add other factories here, if needed.
.build();
You will also need to include the scalars converter in your gradle file --
implementation 'com.squareup.retrofit2:converter-scalars:2.1.0'
--- Original Answer (still works, just more code) ---
I agree with #CommonsWare that it seems a bit odd that you want to intercept the request to process the JSON yourself. Most of the time the POJO has all the data you need, so no need to mess around in JSONObject land. I suspect your specific problem might be better solved using a custom gson TypeAdapter or a retrofit Converter if you need to manipulate the JSON. However, retrofit provides more the just JSON parsing via Gson. It also manages a lot of the other tedious tasks involved in REST requests. Just because you don't want to use one of the features, doesn't mean you have to throw the whole thing out. There are times you just want to get the raw stream, so here is how to do it -
First, if you are using Retrofit 2, you should start using the Call API. Instead of sending an object to convert as the type parameter, use ResponseBody from okhttp --
public interface GitHubService {
#GET("/users/{user}")
Call<ResponseBody> listRepos(#Path("user") String user);
}
then you can create and execute your call --
GitHubService service = retrofit.create(GitHubService.class);
Call<ResponseBody> result = service.listRepos(username);
result.enqueue(new Callback<ResponseBody>() {
#Override
public void onResponse(Response<ResponseBody> response) {
try {
System.out.println(response.body().string());
} catch (IOException e) {
e.printStackTrace();
}
}
#Override
public void onFailure(Throwable t) {
e.printStackTrace();
}
});
Note The code above calls string() on the response object, which reads the entire response into a String. If you are passing the body off to something that can ingest streams, you can call charStream() instead. See the ResponseBody docs.

Android: Realm + Retrofit - Serialize apiresponse

Preface: I'm using Retrofit to handle my API calls and Realm(realm.io) to store the data.
The API im dealing with uses the following structure:
Array Response
{
"response":
[
{
"objectField1":"abc"
"objectField2":"abc"
"objectField3":"abc"
"objectField4":"abc"
},
{
"objectField1":"abc"
"objectField2":"abc"
"objectField3":"abc"
"objectField4":"abc"
}
]
}
Single object response
{
"response":
{
"objectField1":"abc"
"objectField2":"abc"
"objectField3":"abc"
"objectField4":"abc"
}
}
All api responses are contained in a response object either in an array (if result size > 1) or an object (if result size == 1).
I currently have my API call as follows:
#GET("/api/myEndpoint")
void getAllExampleObjects(Callback<MyRealmClass> callback);
How can I serialise the API response (handling both array and single object cases) to place them in my realm?

Christian from Realm here.
If you have a single REST API call that can return both a list and a single object, you will have to do something manually. As colriot points out you will have to write your own GSON deserializer. For ideas how to write one see a very good answer in this SO post: How to handle parameters that can be an ARRAY or OBJECT in Retrofit on Android?
To get the objects into Realm you can use realm.copyToRealm(objects) in the following way:
#GET("/api/myEndpoint")
void getAllExampleObjects(Callback<List<MyRealmClass>> callback);
Callback callback = new Callback() {
#Override
public void success(List<MyRealmClass> objects, Response response) {
realm.beginTransaction();
realm.copyToRealm(objects);
realm.commitTransaction();
}
#Override
public void failure(RetrofitError retrofitError) {
}
};

How to get two objects - raw Response object and POJO - all at once with Retrofit?

I'm using Retrofit/OkHttp in a project and recently I've discovered RxJava. Combining it with Retrofit seems easy and straightforward but with regular async callbacks in Retrofit in success(...) we are receiving the parsed POJO and the Response. This is quite useful and in some of my callbacks I'm using both of these objects. I can't seem to find a way to do this with RxJava.
Is it possible to obtain the parsed POJO and the Response object at the same time?

The way RxJava works is that the onNext method always emits exactly one value, so you won't be able to get something like (as it would break the contract):
onNext(T value, Response respone);
The closest could be an Observable<ResponseAndPojo<T>> where ResponseAndPojo is as follows:
public class ResponseAndPojo<T> {
private final T value;
private final Response response;
public ResponseAndPojo(T value, Response response) {
this.value = value;
this.response = response;
}
// add getters here
}
Such an Observable would then emit items with:
onNext(ResponseAndPojo<T> responseAndPojo)
and you would have access to both the Response and the POJO.
Now, how to construct such an Observable:
One way would be to create some kind of Subject (maybe a BehaviorSubject, but for single requests it does not really matter) and then in the Retrofit success method put the return values into the Subject.
So, in some kind of RetrofitWrapper class of your own you would have
public Observable<ResponseAndPojo<YourPojoClass>> getResponseAndPojoObservable() {
final BehaviorSubject<ResponseAndPojo<YourPojoClass>> retrofitSubject = BehaviorSubject.<ResponesAndPojo<YourPojoClass>>create();
yourRetrofitService.getSomething(new Callback<YourPojoClass>() {
#Override
public void success(YourPojoClass pojo, Response response) {
retrofitSubject.onNext(new ResponseAndPojo(pojo, response);
retrofitSubject.onCompleted();
}
});
return retrofitSubject;
}
As you can see, from the outside the Subject looks like an Observable<ResponseAndPojo<YourPojoClass>>, which is exactly what we wanted.

Custom error handling with Retrofit

The REST Api I'm working with has custom codes and messages which are sent from server depending on the state, I would like to implement a custom Callback<T> that calls the success method only if the status code was 0.
Example SUCCESS Response received from server:
{
"code":"0",
"message":"success",
"data": {
"actual_data":"goes_here",
"need_to_construct_objects","from_data"
}
}
Example of FAILURE Response:
{
"code":"301",
"message":"wrong_password",
"data": {
"actual_data":"will_be_null",
"no_need_to_construct_objects","from_data"
}
}
code and message are returned by all requests, the data contains the actual response values, so I would like to do the following:
Check the code and message and only call success() if code is 0.
Call failure() if request failed or code != 0
Construct custom objects based on the data response and pass them via success()
What is the best way to do this? I searched everywhere and could not find a good solution. The only one I got was to let all custom objects have the code and message fields too and check their values inside success(), but this could cause problems in future in case someone forgets to check the code before proceeding.

You can do that quickly by just making an abstract class that implements Callback, and declare your own abstract success and failure methods. The abstract class will handle Retrofit's standard callback methods, interpret the response and call the abstract methods accordingly.
I think another possible approach to this is to override Retrofit's Client interface to build your own Response object.
If you extend OkClient, it can go like this:
public class CustomClient extends OkClient {
#Override public Response execute(Request request) throws IOException {
Response originalRespone = super.execute(request);
int statusCode = 0;
//TODO: read JSON response here (using GSON or similar, and extract status code and message... etc.)
//Convert the status code to HTTP standard status codes, according to the documentation you have.
if(statusCode == 0) statusCode = 200;
//Reconstruct a Response object
return new Response(originalResponse.getUrl(), statusCode, originalResponse.getReason() /*should probably replace with parsed message*/, originalResponse.getHeaders(), originalResponse.getBody());
}
This may be more work than handling your case in Callback, but I think it can help if at some point the API transitions to RESTful API conventions.
This solution comes with its own problem though, because that means the JSON conversion will run twice. One in your client, and another one by Retrofit. Not sure the correct way to do that at the moment. Probably something around TypedInput and a dummy Converter that passes already converted objects.

Create a custom ResponseBodyConverter like this:
public class CustomResponseBodyConverter<T> implements Converter<ResponseBody, T> {
private final TypeAdapter<T> adapter;
CustomResponseBodyConverter(TypeAdapter<T> adapter) {
this.adapter = adapter;
}
#Override
public T convert(ResponseBody value) throws IOException,CustomException {
String json = "";
try {
String body = value.string();
json = new JSONObject(body).getJSONObject("data").toString();
int code = new JSONObject(body).getInt("code");
String message = new JSONObject(body).getString("message");
if(code != 0){
throw new CustomException(message);
}
} catch (JSONException e) {
e.printStackTrace();
}
return adapter.fromJson(json);
}
}

It's a better idea to implement a custom callback. You can an example about it below.
public abstract class DefaultRequestCallback<T> implements Callback<T> {
public abstract void failure(Meta meta);
public abstract void success(T responseBean);
#Override
public void success(T baseResponseBean, Response response) {
// You can check your responsebean's error code and
// convert it to a default error
BaseResponseBean bean = (BaseResponseBean) baseResponseBean;
if (bean == null) {
failure(new Meta(ApplicationConstants.ERROR_RETROFIT, "Unknown Error!"));
} else if (bean.getMeta() != null && bean.getMeta().getCode() != ApplicationConstants.RESULT_SUCCESS) {
failure(bean.getMeta());
} else {
success(baseResponseBean);
}
}
#Override
public void failure(RetrofitError error) {
// Convert default error to your custom error.
Meta meta = new Meta(ApplicationConstants.ERROR_RETROFIT, "Error Unknwon");
failure(meta);
}
}
Give your custom callback to your retrofit service interface method.
void yourMethod(DefaultRequestCallback<YourResponseBean> callback);
Good Luck.

This will at least get you started. You can basically create your own custom callback and then handle the success. Look at what was sent and do what you need to.
public class CustomCallback implements Callback {
#Override
public void success(Object o, Response response) {
//Check for success
//if( Success )
//callback.success(o, response);
//else
//Check for error
//callback.failure(error);
}
}

In your case, you can have a class that maps your json response:
class CustomResponse {
String code;
String message;
Data data;
static class Data {
String actualData;
String needToContructObjects;
String noNeedToContructObjects;
}
}
Then, since you're back to the java objects world, you can have a factory-like object inside your success method callback that creates the desired object based on the returned custom response. If you want to get this response in the failure callback, I'd reconsider using Retrofit, since your API is not following a good Rest design.
Although this is plenty possible, and understanding you might not be involved on the API development, be aware this is not a good API design approach. If you are POSTing a login request to the server, you can understand this request as a request to create a resource (an authenticated user session, for instance). If you don't send the correct parameters (the correct username and password in this specific case), the server should reject the resource creation request and send back a 4-hundred-something (4xx) http status code indicating your request was not correct somehow. Retrofit would understand this 4xx status code and call your failure callback, where you could handle the response appropriately.