Moshi didn't recognize ArrayList data class "com.squareup.moshi.JsonDataException: Expected BEGIN_OBJECT but was BEGIN_ARRAY at path $"

Question

I practicing on Retrofit with Moshi, in this simple demo app I trying to get list of albums and log it, but I got this exception after running the app

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.anushka.retrofitdemo, PID: 12428
    com.squareup.moshi.JsonDataException: Expected BEGIN_OBJECT but was BEGIN_ARRAY at path $
        at com.squareup.moshi.JsonUtf8Reader.beginObject(JsonUtf8Reader.java:172)
        at com.squareup.moshi.kotlin.reflect.KotlinJsonAdapter.fromJson(KotlinJsonAdapter.kt:67)
        at com.squareup.moshi.internal.NullSafeJsonAdapter.fromJson(NullSafeJsonAdapter.java:41)
        at retrofit2.converter.moshi.MoshiResponseBodyConverter.convert(MoshiResponseBodyConverter.java:46)
        at retrofit2.converter.moshi.MoshiResponseBodyConverter.convert(MoshiResponseBodyConverter.java:27)
        at retrofit2.OkHttpCall.parseResponse(OkHttpCall.java:243)
        at retrofit2.OkHttpCall$1.onResponse(OkHttpCall.java:153)
        at okhttp3.internal.connection.RealCall$AsyncCall.run(RealCall.kt:504)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
        at java.lang.Thread.run(Thread.java:923)

Data classes

AlbumsItem

@JsonClass(generateAdapter = true)
data class AlbumsItem(
    @Json(name = "id")
    val id: Int,
    @Json(name = "title")
    val title: String,
    @Json(name = "userId")
    val userId: Int
)

Albums List class

@JsonClass(generateAdapter = false)
class Albums : ArrayList<AlbumsItem>()

the service

interface AlbumsService {

    @GET("albums")
    suspend fun getAlbums(): Response<Albums>
}

The instance of retrofit

class RetrofitInstance {
    companion object {
        private const val BASE_URL = "https://jsonplaceholder.typicode.com/"

        var moshi = Moshi.Builder()
            .add(KotlinJsonAdapterFactory())
            .build()


        fun getRetrofitInstance(): Retrofit {

            return Retrofit.Builder()
                .baseUrl(BASE_URL)
                .addConverterFactory(MoshiConverterFactory.create(moshi))
                .build()

        }
    }
}

and finally the MainActivity

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val retService = RetrofitInstance.getRetrofitInstance().create(AlbumsService::class.java)

        val responseLiveData: LiveData<Response<Albums>> = liveData {
            val response:Response<Albums> = retService.getAlbums()
            emit(response)
        }

        responseLiveData.observe(this, {
            val albumsList = it.body()?.listIterator()
            if (albumsList != null) {
                while (albumsList.hasNext()) {
                  albumsList.forEach {
                      Log.d(TAG, "album data by title: ${it.title}")
                  }
                }
            }
        })
    }
}

and while I searching for the cause and solution of this error, I see this question and it look the Moshi cannot recognize the data class Albums and I don't know why, but after I changed the structure of service instead using Albums class to List it's work fine

I replaced the service like this

@GET("albums")
suspend fun getAlbums(): Response<List<AlbumsItem>>

and call it like this

val responseLiveData: LiveData<Response<List<AlbumsItem>>> = liveData {
            val response:Response<List<AlbumsItem>> = retService.getAlbums()
            emit(response)
        }

PS: I tried this annotation @JsonClass(generateAdapter = true) and with value false above the Albums class but it doesn't work, also I tried using GsonConverterFactory with Albums class it's recognize it without problem, so How can I make the moshi recognize it?

Moshi, by design, won't decode platform classes like ArrayList (which your class subclasses) without an explicit registered adapter. This error message should be better (it used to have text about platform classes); maybe file a bug on Moshi for a better error message. — Eric Cochran, Sep 09 '21 at 16:51
@kzone sorry I can't remember if it's solved or not, but I used the old Gson lib now — Dr Mido, Jan 14 '23 at 14:25

score 0 · Answer 1 · answered Jul 22 '22 at 12:57

Maybe for someone it will works. In my case I changed

This:

return Retrofit.Builder().addConverterFactory(MoshiConverterFactory.create(MyMoshiObject).asLenient())                                    
    .baseUrl(Constants.BASE_URL).                              
    .client(okHttpClient)                                                  
    .build().

To this:

return Retrofit.Builder()
.addConverterFactory(MoshiConverterFactory.create().asLenient())
            .baseUrl(Constants.BASE_URL).                              
            .client(okHttpClient)                                                  
            .build()

Just removed Moshi object in create()

Moshi didn't recognize ArrayList data class "com.squareup.moshi.JsonDataException: Expected BEGIN_OBJECT but was BEGIN_ARRAY at path $"

1 Answers1