Recently, version 1.4.0 added integration with the Okio library, the same library used by Moshi under the hood. The JSON engine had also been rewritten in the meantime in order to improve performance. The lack of initial support for streaming was disappointing, so I didn’t even consider using it in production until streaming support was eventually added in version 1.3.0 in 2021. This library generates adapters at compile time similarly to Moshi’s annotation processor while being compatible with more platforms and formats. JetBrains released version 1.0.0 of Kotlin Serialization in 2020 with built-in support for JSON.

I was quite interested in the performance gains allowed by this solution and wrote an article detailing what the generated code does. One year later, the next major release 1.6.0 added an annotation processor to generate adapters for Kotlin classes at compile time. Moshi has been supporting Kotlin classes since version 1.5.0, released in 2017. If you’re still using legacy libraries like Gson to parse Kotlin classes, it’s time to reconsider. This compatibility is especially important for non-null types and default values during deserialization, where lack of proper Kotlin support could result in unexpected values occurring at runtime, such as null values in non-null fields. When it comes to automatic serialization and deserialization of Kotlin classes using the JSON format, the two main libraries compatible with Kotlin metadata are currently Moshi and Kotlin Serialization.

Android kotlin serialization