How to handle 4XX response

Hi, thanks for great library. I have a question about handling 400 response.

I am developing an Android application on Kotlin and use rx_responseString() method to get a JSON from a Web API.

Api responses a JSON like bellow.

{
    "firstName": "hoge"
    "lastName" : "foo"
}

Data class for response.

data class User(val firstName: String, val lastName: String)

I want to get a User object from a api’s response with GSON.

// In a data access class
fun getUser(): Single<User> {

  // send a get request and convert response
  return "http://XXX/user".httpGet().rx_responseString()
    map {
      p ->
      val gson = Gson()
      gson.fromJson(p.second.get(), User::class.java)
    }
}

In an activity, I retrieve s result and display. When response status code is 4XX, I want to display error dialog with message.

// In an Activity
getUser().subscribeOn(Schedulers.newThread())
         .observeOn(AndroidSchedulers.mainThread())
         .subscribe(
         {
            // onSuccess
            res ->
              // display json to an Activity
         },
         {
            // onError
            e ->
              // check http status code
              when (httpStatusCode) {
                400 -> {
                     // show dialog with message
                }
                404 -> {
                    // show dialog with message
                } 
         }
         )

I want to know best practices to handle response with status code 4XX.

[keizo2]

Thank you for replying! If I apply clean architecture like https://blog.uptech.team/clean-architecture-in-android-with-kotlin-rxjava-dagger-2-2fdc7441edfc, I guess it’s better to keep the return type of getUser method Single<User> and tried to return an error object in an exception as below. How is this?

// error object
data class ApiError(val errorCode: String, val message: String)

// the field contains an Api Error object.
class ApiException(val apiError: QiitaError) : Exception()

fun getUser(): Single<User> {

    return url.httpGet().rx_responseString().flatMap { p ->
        when (p.first.httpStatusCode) {
            200 -> {
                val gson = Gson()
                Single.create<User> { e ->
                    e.onSuccess(gson.fromJson(p.second.get(), User::class.java))
                }
            }
            400..419 -> {
                // handle an 4XX error 
                val input = InputStreamReader(ByteArrayInputStream(p.first.data))
                val gson = Gson()
                val error = gson.fromJson(input, ApiError::class.java)
                Single.error(QiitaException(error))
            }
            else -> {}
        }
    }

[babedev]

you can check statusCode in res object

getUser().subscribeOn(Schedulers.newThread())
         .observeOn(AndroidSchedulers.mainThread())
         .subscribe({ res ->
            val statusCode = res.first.statusCode
            when (statusCode) {
               400 -> { }
               401 -> { }
            }
         }, { e -> })

hope this answer your question 😃