Moshi: [Kotlin Codegen] Issue with generated adapter for Kotlin generic-classes

[green-nick]

I spent a lot of time to make Moshi works with my generics classes, but it still throws java.lang.RuntimeException on every attempt to serialize object to the json.

There is minimal example:

import com.squareup.moshi.JsonClass
import com.squareup.moshi.Moshi

interface ParamsRequest

@JsonClass(generateAdapter = true)
class RpcRequest<out T : ParamsRequest>(
    val method: String,
    val params: T? = null
) {
    val id: String = "vsdv"
    val jsonrpc: String = "2.0"
}

@JsonClass(generateAdapter = true)
class SeedRequest(val key_type: String = "mnemonic") : ParamsRequest

inline fun <reified T> T.toJson(): String = Moshi.Builder().build()
    .adapter(T::class.java)
    .toJson(this)

fun runTest() {
    val request = RpcRequest("method", SeedRequest())
    println("json: [${request.toJson()}]")
}

Used dependecies:

com.squareup.moshi:moshi:1.8.0
com.squareup.moshi:moshi-kotlin-codegen:1.8.0

Stacktrace:

    java.lang.RuntimeException: Failed to find the generated JsonAdapter constructor for class com.example.paulg.myapplication.RpcRequest
        at com.squareup.moshi.internal.Util.generatedAdapter(Util.java:484)
        at com.squareup.moshi.StandardJsonAdapters$1.create(StandardJsonAdapters.java:60)
        at com.squareup.moshi.Moshi.adapter(Moshi.java:137)
        at com.squareup.moshi.Moshi.adapter(Moshi.java:97)
        at com.squareup.moshi.Moshi.adapter(Moshi.java:71)
        at com.example.paulg.myapplication.TestKt.runTest(Test.kt:34)
        at com.example.paulg.myapplication.MainActivity$onCreate$1.onClick(MainActivity.kt:19)
        at android.view.View.performClick(View.java:6597)
        at android.view.View.performClickInternal(View.java:6574)
        at android.view.View.access$3100(View.java:778)
        at android.view.View$PerformClick.run(View.java:25885)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6680)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: java.lang.NoSuchMethodException: <init> [class com.squareup.moshi.Moshi]
        at java.lang.Class.getConstructor0(Class.java:2327)
        at java.lang.Class.getDeclaredConstructor(Class.java:2166)
        at com.squareup.moshi.internal.Util.generatedAdapter(Util.java:476)
        at com.squareup.moshi.StandardJsonAdapters$1.create(StandardJsonAdapters.java:60) 
        at com.squareup.moshi.Moshi.adapter(Moshi.java:137) 
        at com.squareup.moshi.Moshi.adapter(Moshi.java:97) 
        at com.squareup.moshi.Moshi.adapter(Moshi.java:71) 
        at com.example.paulg.myapplication.TestKt.runTest(Test.kt:34) 
        at com.example.paulg.myapplication.MainActivity$onCreate$1.onClick(MainActivity.kt:19) 
        at android.view.View.performClick(View.java:6597) 
        at android.view.View.performClickInternal(View.java:6574) 
        at android.view.View.access$3100(View.java:778) 
        at android.view.View$PerformClick.run(View.java:25885) 
        at android.os.Handler.handleCallback(Handler.java:873) 
        at android.os.Handler.dispatchMessage(Handler.java:99) 
        at android.os.Looper.loop(Looper.java:193) 

[green-nick]

There is also generated adapter:

import com.squareup.moshi.JsonAdapter
import com.squareup.moshi.JsonDataException
import com.squareup.moshi.JsonReader
import com.squareup.moshi.JsonWriter
import com.squareup.moshi.Moshi
import java.lang.NullPointerException
import java.lang.reflect.Type
import kotlin.Array
import kotlin.Boolean
import kotlin.String

class RpcRequestJsonAdapter<T : ParamsRequest>(moshi: Moshi, types: Array<Type>) : JsonAdapter<RpcRequest<T>>() {
    private val options: JsonReader.Options = JsonReader.Options.of("method", "params")

    private val stringAdapter: JsonAdapter<String> =
            moshi.adapter<String>(String::class.java, kotlin.collections.emptySet(), "method")

    private val nullableTParamsRequestAdapter: JsonAdapter<T?> =
            moshi.adapter<T?>(types[0], kotlin.collections.emptySet(), "params")

    override fun toString(): String = "GeneratedJsonAdapter(RpcRequest)"

    override fun fromJson(reader: JsonReader): RpcRequest<T> {
        var method: String? = null
        var params: T? = null
        var paramsSet: Boolean = false
        reader.beginObject()
        while (reader.hasNext()) {
            when (reader.selectName(options)) {
                0 -> method = stringAdapter.fromJson(reader) ?: throw JsonDataException("Non-null value 'method' was null at ${reader.path}")
                1 ->  {
                    params = nullableTParamsRequestAdapter.fromJson(reader)
                    paramsSet = true
                }
                -1 -> {
                    // Unknown name, skip it.
                    reader.skipName()
                    reader.skipValue()
                }
            }
        }
        reader.endObject()
        var result = RpcRequest<T>(
                method = method ?: throw JsonDataException("Required property 'method' missing at ${reader.path}"))
        result = RpcRequest<T>(
                method = method,
                params = if (paramsSet) params else result.params)
        return result
    }

    override fun toJson(writer: JsonWriter, value: RpcRequest<T>?) {
        if (value == null) {
            throw NullPointerException("value was null! Wrap in .nullSafe() to write nullable values.")
        }
        writer.beginObject()
        writer.name("method")
        stringAdapter.toJson(writer, value.method)
        writer.name("params")
        nullableTParamsRequestAdapter.toJson(writer, value.params)
        writer.endObject()
    }
}

[swankjesse]

Unfortunately you're asking Moshi to give you the JsonAdapter for RpcRequest instead of RpcRequest<SeedRequest>. Use Types.newParameterizedType(...) to do that.

[green-nick]

I see now, thanks a lot. This helps me

[zakayothuku]

How do you use Types.newParameterizedType(...) to do that as it is not in the documentation?

[ZacSweers]

It is documented here: https://github.com/square/moshi/blob/master/moshi/src/main/java/com/squareup/moshi/Types.java#L107-L110

[zakayothuku]

Am still new to Moshi, do you have an example showing this is done?

[ZacSweers]

Tests. For usage questions please ask on stackoverflow with the Moshi tag

On Wed, Sep 18, 2019 at 1:45 PM Zakayo Thuku [e-mail]
wrote:

Am still new to Moshi, do you have an example showing this is done?

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[limuyang2]

Am still new to Moshi, do you have an example showing this is done?

Examples:

@JsonClass(generateAdapter = true)
data class BaseBean<T>(val code: Int, val msg: T)

@JsonClass(generateAdapter = true)
data class InfoData(val name: String = "")

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

val type = Types.newParameterizedType(BaseBean::class.java, InfoData::class.java)
val jsonAdapter: JsonAdapter<BaseBean<InfoData>> = moshi.adapter(type)
val baseBean = jsonAdapter.fromJson(jsonStr)!!