Moshi 1.9.x Cannot serialize Kotlin type

Question

I'm running into the following crash and stack trace after upgrading to Moshi 1.9.1 (from 1.8.0):

java.lang.IllegalArgumentException: Cannot serialize Kotlin type com.garpr.android.data.models.RankedPlayer. Reflective serialization of Kotlin classes without using kotlin-reflect has undefined and unexpected behavior. Please use KotlinJsonAdapter from the moshi-kotlin artifact or use code gen from the moshi-kotlin-codegen artifact.
for class com.garpr.android.data.models.RankedPlayer
for class com.garpr.android.data.models.AbsPlayer

    at com.squareup.moshi.Moshi$LookupChain.exceptionWithLookupStack(Moshi.java:349)
    at com.squareup.moshi.Moshi.adapter(Moshi.java:150)
    at com.squareup.moshi.Moshi.adapter(Moshi.java:98)
    at com.squareup.moshi.AdapterMethodsFactory$AdapterMethod.bind(AdapterMethodsFactory.java:313)
    at com.squareup.moshi.AdapterMethodsFactory.create(AdapterMethodsFactory.java:62)
    at com.squareup.moshi.Moshi.adapter(Moshi.java:138)
    at com.squareup.moshi.Moshi.adapter(Moshi.java:98)
    at com.squareup.moshi.Moshi.adapter(Moshi.java:72)
    at com.garpr.android.data.converters.AbsPlayerConverterTest.setUp(AbsPlayerConverterTest.kt:76)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:24)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
    at org.robolectric.RobolectricTestRunner$HelperTestRunner$1.evaluate(RobolectricTestRunner.java:546)
    at org.robolectric.internal.SandboxTestRunner$2.lambda$evaluate$0(SandboxTestRunner.java:252)
    at org.robolectric.internal.bytecode.Sandbox.lambda$runOnMainThread$0(Sandbox.java:89)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.IllegalArgumentException: Cannot serialize Kotlin type com.garpr.android.data.models.RankedPlayer. Reflective serialization of Kotlin classes without using kotlin-reflect has undefined and unexpected behavior. Please use KotlinJsonAdapter from the moshi-kotlin artifact or use code gen from the moshi-kotlin-codegen artifact.
    at com.squareup.moshi.ClassJsonAdapter$1.create(ClassJsonAdapter.java:83)
    at com.squareup.moshi.Moshi.nextAdapter(Moshi.java:169)
    at com.squareup.moshi.AdapterMethodsFactory$AdapterMethod.bind(AdapterMethodsFactory.java:312)
    at com.squareup.moshi.AdapterMethodsFactory.create(AdapterMethodsFactory.java:62)
    at com.squareup.moshi.Moshi.adapter(Moshi.java:138)
    ... 23 more

I saw this other Stack Overflow answer, but it does not apply to me, as I've already added the relevant @JsonClass(generateAdapter = X) line to my classes.

I use a custom AbsPlayerConverter class for my AbsPlayer class, this is used so that I can determine which subclass to resolve to. And then, if it resolves to RankedPlayer, I use another custom converter for that (RankedPlayerConverter).

Here is my Moshi-builder code:

Moshi.Builder()
        .add(AbsPlayerConverter)
        .add(AbsRegionConverter)
        .add(AbsTournamentConverter)
        .add(MatchConverter)
        .add(RankedPlayerConverter)
        .add(SimpleDateConverter)
        .build()

And here is Moshi in my gradle file:

implementation "com.squareup.moshi:moshi:1.9.1"
kapt "com.squareup.moshi:moshi-kotlin-codegen:1.9.1"

So finally, after all of that text and info, I have no idea how I can be running into this crash. I clearly have defined how to serialize/deserialize my RankedPlayer class. And if I downgrade to Moshi 1.8.0, and leave my codebase completely as-is, this crash goes away and everything works flawlessly.

Anyone have any ideas?

Thanks!!

Answer 1

The error message specifically says Please use KotlinJsonAdapter from the moshi-kotlin artifact or use code gen from the moshi-kotlin-codegen artifact

As per the Kotlin part of the readme, you must add the KotlinJsonAdapterFactory if you're not using Moshi's codegen. This was a specific behavior change in Moshi 1.9 as per the blog post about Moshi 1.9.

Moshi.Builder()
    .add(AbsPlayerConverter)
    .add(AbsRegionConverter)
    .add(AbsTournamentConverter)
    .add(MatchConverter)
    .add(RankedPlayerConverter)
    .add(SimpleDateConverter)
    .add(KotlinJsonAdapterFactory())
    .build()

And make sure you're using implementation("com.squareup.moshi:moshi-kotlin:1.9.1")

Answer 2

I'm using retrofit and I had to do the following:

In the build.grade:

implementation "com.squareup.moshi:moshi-kotlin:$moshiVersion"

In my repository:

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

val retrofit = Retrofit.Builder()
    .baseUrl(WEB_SERVICE_URL)
    .addConverterFactory(MoshiConverterFactory.create(moshi))
    .build()