Android:dynamically pass model class to retrofit callback

Question

In retrofit to map json response to pojo usually we do this

@POST
Call getDataFromServer(@Url String url, @Body HashMap ha         


        

Answer 1

I use following approach: First I have implemented custom Call

public class ProxyConvertCall implements Call {
    Converter converter;
    Call innerCall;

    public ProxyConvertCall2(Call jcall, Converter converter){
        this.innerCall = jcall;
        this.converter = converter;
        }

    @Override
    public Response execute() throws IOException {
        Response response = innerCall.execute();
        if (response.isSuccessful()){
            return Response.success(converter.Convert(response.body()),response.raw());
        }
        else return Response.error(response.code(), response.errorBody());
    }

    @Override
    public void enqueue(final Callback callback) {
        final Call self = this;
        this.innerCall.enqueue(new Callback() {  
            @Override
            public void onResponse(Call call, Response response) {
                if (response.isSuccessful()){
                    callback.onResponse(self, Response.success(converter.Convert(response.body()), response.raw()));
                }
                else callback.onResponse(self, Response.error(response.code(), response.errorBody()));
            }
            @Override
            public void onFailure(Call call, Throwable t) {
                callback.onFailure(self,t);
            }
        });

    }

    @Override
    public boolean isExecuted() {
        return innerCall.isExecuted();
    }

    @Override
    public void cancel() {
        innerCall.cancel();

    }

    @Override
    public boolean isCanceled() {
        return innerCall.isCanceled();
    }

    @Override
    public Call clone() {
        return new ProxyConvertCall2<>(innerCall,converter);
    }

    @Override
    public Request request() {
        return innerCall.request();
    }
}

It wrappes Call and converts it's result to by converter.

@FunctionalInterface 
public interface Converter {
    public Tout Convert(Tin in);
}

For your service you must create service interface, that return JsonObject for single object and JsonArray for arrays

public interface ApiCalls {
    @POST
    Call getDataFromServer(@Url String url, @Body HashMap hashMap);

    @POST
    Call getArrayFromServer(@Url String url, @Body HashMap hashMap);
}

Then wrap it with generic class, with converters from JsonElement to any Type :

public class ApiCallsGeneric {
    Converter fromJsonObject;
    Converter> fromJsonArray;
    ApiCalls service;

    public ApiCallsGeneric(Class classOfT, ApiCalls service){    
        this.service = service;
        Gson gson  = new GsonBuilder().create();
        GenericListType genericListTypeOfT = new GenericListType(classOfT);
        fromJsonObject = (t)->gson.fromJson(t,classOfT);
        fromJsonArray =(t)->gson.fromJson(t,genericListTypeOfT);
    }

    public Call getDataFromServer(String url, HashMap hashMap){
        return new ProxyConvertCall<>(service.getDataFromServer(url, hashMap), fromJsonObject);
     }

    public Call> getArrayFromServer(String url, HashMap hashMap){ 
        return new ProxyConvertCall<>(service.getArrayFromServer(url, hashMap), fromJsonArray);
     }
}

GenericListType is ParaterizedType. It is used for passing type parameter to gson for List

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.List;

public class GenericListType implements ParameterizedType {

    private Type wrapped;

    public GenericListType(Type wrapped) {
        this.wrapped = wrapped;
    }

    public Type[] getActualTypeArguments() {
        return new Type[] {wrapped};
    }

    public Type getRawType() {
        return  List.class;
    }

    public Type getOwnerType() {
        return null;
    }

}

Then you can instantiate ApiCallsGeneric with type you want.

ApiCallsGeneric userService= new ApiCallsGeneric(User.class, retrofit.create(ApiCalls.class));
Call call = userService.getDataFromServer(StringConstants.URL,hashMap);
call.enqueue(new Callback() {
         //Response and failure callbacks
    }