moshi-sealed

Introduction: Reflective and code gen implementations for serializing Kotlin sealed classes via Moshi polymorphic adapters.
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Reflective and code gen implementations for serializing Kotlin sealed classes via Moshi polymorphic adapters.

Simple annotated a sealed class with @JsonClass with a generator value of sealed:{typeLabel}. {typeLabel} is the value of the type label that should be used for a Moshi PolymorphicJsonAdapterFactory. Annotate subtypes with @TypeLabel to indicate their type label value. One object can be used as an unknown default value via @DefaultObject, or the sealed type can be annotated with @DefaultNull to indicate that null should be the default.

@JsonClass(generateAdapter = true, generator = "sealed:type")
sealed class Message {

  @TypeLabel("success")
  @JsonClass(generateAdapter = true)
  data class Success(val value: String) : Message()

  @TypeLabel("error")
  @JsonClass(generateAdapter = true)
  data class Error(val error_logs: Map<String, Any>) : Message()

  @DefaultObject
  object Unknown : Message()
}

Installation

Moshi-sealed can be used via reflection or code generation. Note that you must include the moshi-adapters artifact as a dependency, as that's where the PolymorphicJsonAdapter implementation lives.

@TypeLabel and default indicator annotations are available in the moshi-sealed-annotations artifact.

Maven Central

implementation "dev.zacsweers.moshisealed:moshi-sealed-annotations:{version}"

Code gen

Code gen works via annotation processor, and only requires adding the kapt dependency:

Maven Central

kapt "dev.zacsweers.moshisealed:moshi-sealed-codegen:{version}"

No runtime Moshi instance configuration is needed, code gen will generate JsonAdapters in a way that Moshi understands natively.

Reflection

Reflection works via MoshiSealedJsonAdapterFactory. Just add this in moshi before KotlinJsonAdapterFactory in your Moshi instance construction.

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

Gradle dependency:

Maven Central

implementation "dev.zacsweers.moshisealed:moshi-sealed-reflect:{version}"

Snapshots of the development version are available in Sonatype's snapshots repository.

License

Copyright (C) 2019 Zac Sweers

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
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