An annotations processor that generates Moshi adapters from immutable Kotlin data classes.

Moshi's default reflective adapters assume your classes are compiled from Java code which causes problem for Kotlin data classes.

There is a reflective adapter for Kotlin but that requires the kotlin reflection library which adds a lot of methods and increase the binary size which in a constrained environment such as Android is something is not preferable.

This is where Kotshi comes in, it generates fast and optimized adapters for your Kotlin data classes, just as if you'd hand written them yourself. It will automatically regenerate the adapters when you modify your class.

It's made to work with Kotlin data classes with minimal setup, through there are limitations. Most of the limitations will be addressed when the support for Kotlin annotation processors improves.

First you must annotate your Kotlin data classes with the @JsonSerializable annotation:

@JsonSerializable
data class Person(
    val name: String,
    val email: String?,
    val hasVerifiedAccount: Boolean,
    // This property has a different name in the Json than here so @Json must be applied.
    @Json(name = "created_at")
    val signUpDate: Date,
    // This field has a default value which will be used if the field is missing.
    val jobTitle: String? = null
)

Then create a class that will be your factory:

@KotshiJsonAdapterFactory
abstract class ApplicationJsonAdapterFactory : JsonAdapter.Factory {
  val INSTANCE: ApplicationJsonAdapterFactory = KotshiApplicationJsonAdapterFactory
}

Lastly just add the factory to your Moshi instance and you're all set:

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

By default adapters aren't requested for primitive types (even boxed primitive types) since it is worse for performance and most people will not have custom adapters anyway. If you need to use custom adapters you can enable it per module be passing the useAdaptersForPrimitives to @KotshiJsonAdapterFactory or on a per adapter by passing the same argument to @JsonSerializable (the default is to follow the module wide setting).

• @JsonSerializable is the annotation used to generate JsonAdapter's. Should only be placed on Kotlin data classes.
• @KotshiJsonAdapterFactory makes Kotshi generate a JsonAdapter factory. Should be placed on an abstract class that implements JsonAdapter.Factory.

You can use default values just like you normally would in Kotlin.

Due to limitations in Kotlin two instances of the object will be created when a class uses default values (youtrack issue). This also means that composite default values are not supported (for example a fullName property that is "$firstName $lastName").

Properties marked with @Transient are not serialized. All transient properties must have a default value.

Only properties declared in the constructor needs to be annotated since other properties are ignores.

• Kotshi only processes files written in Kotlin, types written in Java are not support.
• Only data classes are supported.
  • Only constructor properties will be serialized.
• Due to limitation in KAPT properties with a java keyword as a name cannot be marked as transient.
• Default values that depend on other constructor properties is not supported (youtrack issue).

implementation 'se.ansman.kotshi:api:2.0.1'
kapt 'se.ansman.kotshi:compiler:2.0.1'

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

Copyright 2017-2019 Nicklas Ansman Giertz.

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.