This is customized retrofit rest api client for android

Rester

package com.osellers.common.restclient

import android.content.Context
import com.durbinlabs.duplate.common.utils.U
import com.osellers.common.BuildConfig
import com.osellers.common.utils.C
import com.osellers.common.utils.D
import com.osellers.common.utils.Lg
import io.reactivex.Observable
import io.reactivex.Observer
import io.reactivex.android.schedulers.AndroidSchedulers
import io.reactivex.disposables.CompositeDisposable
import io.reactivex.disposables.Disposable
import io.reactivex.schedulers.Schedulers
import okhttp3.OkHttpClient
import okhttp3.ResponseBody
import okhttp3.logging.HttpLoggingInterceptor
import retrofit2.Response
import retrofit2.Retrofit
import retrofit2.adapter.rxjava2.RxJava2CallAdapterFactory
import retrofit2.converter.gson.GsonConverterFactory
import retrofit2.http.GET
import retrofit2.http.POST

object Rester {

    private val TAG = Rester::class.java.simpleName

    @Suppress("KDocUnresolvedReference")
    enum class API {
        LOGIN
    }

    private interface MyService {
        @POST("/api_reg/login")
        fun login(ep: String, password: String): Observable<Response<ResponseBody>>
    }

    @JvmStatic
    fun execute(context: Context, api: API, params: Array<Any>?, callback: ResterCallBack<Response<ResponseBody>>) {
        execute(context, api, params, callback, false, null)
    }

    @JvmStatic
    fun execute(
            context: Context, api: API, params: Array<Any>?, callback: ResterCallBack<Response<ResponseBody>>,
            noInternetSilentCallBack: NoInternetSilentCallBack?) {
        execute(context, api, params, callback, true, noInternetSilentCallBack)
    }

    @JvmStatic
    fun execute(
            context: Context, api: API, params: Array<Any>?, callback: ResterCallBack<Response<ResponseBody>>,
            isToPromptNet: Boolean, noInternetSilentCallBack: NoInternetSilentCallBack?) {

        if (!U.isNetConnected(context)) {
            noInternetSilentCallBack?.notifyHasInternet(false)

            if (isToPromptNet)
                D.showNoInternetDialog(context) { execute(context, api, params, callback, isToPromptNet, noInternetSilentCallBack) }
            return
        } else noInternetSilentCallBack?.notifyHasInternet(true)

        val retrofit = RestApiClient.getRetrofit(context)

        val call = when (api) {
            API.LOGIN -> retrofit.create(MyService::class.java).login(params!![0].toString(), params[1].toString())
        }

        /*call?.enqueue(object : Callback<ResponseBody> {
            override fun onFailure(call: Call<ResponseBody>, e: Throwable) {
                callback.onError(e)
                e.printStackTrace()
            }

            override fun onResponse(call: Call<ResponseBody>, response: Response<ResponseBody>) {
                callback.onResponse(response)

                Lg.d(TAG, response.body()?.string())
            }
        })*/


        call.subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(object : Observer<retrofit2.Response<ResponseBody>> {
                    override fun onComplete() {

                    }

                    override fun onSubscribe(d: Disposable) {
                        RxJavaDisposableManager.add(d)
                    }

                    override fun onNext(response: retrofit2.Response<ResponseBody>) {
                        callback.onResponse(response)
                        Lg.d(TAG, response.body()?.string())
                    }

                    override fun onError(e: Throwable) {
                        callback.onError(e)
                        e.printStackTrace()
                    }
                })
    }

    // A rest api client which works with rxjava
    private object RestApiClient {
        private var retrofit: Retrofit? = null
        private var okHttpClient: OkHttpClient? = null
        private var loggingInterceptor: HttpLoggingInterceptor? = null
        private var rxAdapter =
                RxJava2CallAdapterFactory.createWithScheduler(Schedulers.io())


        fun getRetrofit(context: Context): Retrofit {
            if (retrofit == null) {
                retrofit = create(context)
            }
            return retrofit!!
        }

        private fun create(context: Context): Retrofit {
            // Level.BODY
            /*shows all the information of a request. We just want to see info when app
            * is in debug mode*/
            loggingInterceptor = HttpLoggingInterceptor()
            if (BuildConfig.DEBUG)
                loggingInterceptor!!.level = HttpLoggingInterceptor.Level.BODY
            else loggingInterceptor!!.level = HttpLoggingInterceptor.Level.BASIC

            okHttpClient = OkHttpClient.Builder().addInterceptor(loggingInterceptor!!).build()

            return Retrofit.Builder()
                    .baseUrl(C.SERVER_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .addCallAdapterFactory(rxAdapter)
                    .client(okHttpClient!!)
                    .build()
        }
    }

    object RxJavaDisposableManager {
        private var compositeDisposable: CompositeDisposable? = null

        fun add(disposable: Disposable) {
            getCompositeDisposable().add(disposable)
        }

        fun dispose() {
            getCompositeDisposable().dispose()
        }

        private fun getCompositeDisposable(): CompositeDisposable {
            if (compositeDisposable == null || compositeDisposable!!.isDisposed) {
                compositeDisposable = CompositeDisposable()
            }
            return compositeDisposable!!
        }

    }

    /**
     * Created by touhid on 7/10/16.
     *
     * @author touhid
     */
    interface NoInternetSilentCallBack {
        fun notifyHasInternet(isNetOn: Boolean)
    }

    /**
     * Created by Shaon on 7/10/18.
     *
     * @author Shaon
     */
    interface ResterCallBack<T> {
        fun onResponse(response: T)
        fun onError(e: Throwable)
    }

    /**
     * Created by touhid on 7/10/16.
     *
     * @author touhid
     */
    interface RetryCallBackForNoInternet {
        fun retry()
    }
}