Service Generator Retrofit

Question

Can someone help me understand the createService method in below code. I need to understand what is method's parameter Class S and the code underneath in depth

public class ServiceGenerator {

public static final String API_BASE_URL = Constant.BASE_URL;

private static OkHttpClient httpClient = new OkHttpClient();

private static Retrofit.Builder builder =
        new Retrofit.Builder()
                .baseUrl(API_BASE_URL)
                .addConverterFactory(GsonConverterFactory.create());

public static <S> S createService(Class<S> serviceClass) {
    httpClient.interceptors().add(new Interceptor() {
        @Override
        public Response intercept(Chain chain) throws IOException {
            Request original = chain.request();

            Request.Builder requestBuilder = original.newBuilder()
                    .header("cache-control","no-cache")
                    .method(original.method(), original.body());

            Request request = requestBuilder.build();
            return chain.proceed(request);
        }
    });

    Retrofit retrofit = builder.client(httpClient).build();
    return retrofit.create(serviceClass);
}

}

Answer 1

Found the answer myself. The entire createservice method is not absolute necessity in this code and one can live without interceptor declarations as shown below. If someone wants to set interceptor methods for httpClient such as cache-control, authorization token etc, one can use the complete code block to set them. The simplest version of createService is

public class ServiceGenerator {
    public static <S> S createService(Class<S> serviceClass) {
        Retrofit retrofit = builder.client(httpClient).build();
        return retrofit.create(serviceClass);
    }
}

Here "S" is a class type parameter. It is used to specify that the output type class to be same as input class. Then you can create you own api interface simply using this code in any activity/fragment

MyApiService myapiservice = ServiceGenerator.createService(MyApiServiceInterface.class)
Call<YourDataResponseClass> call = myapiService.getMyData(YourDataRequestClass);
call.enqueue ({.....remaining code})

Define your MyApiService as below

public interface MyApiServiceInterface {
        /*Base url is already defined in service generator class*/
        @GET("/your/api/endpoint/")
        /*YourDataResponseClass and YourDataRequestClass are 
        pojo object notation of your request and response json*/
        YouDataResponseClass getMyData(
                @Body YourDataRequestClass request
        );
    }