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Introducing Helios for Kotlin

Introducing Helios for Kotlin

Helios is a library for JSON handling that’s compatible with all of Kotlin’s types including nullable types and data classes, with few Java types like UUID and BigDecimal and, also, with some Arrow data types, Option, Either, and Tuple for example.

Let’s take a brief look at how you can start using Helios:

Adding the dependency

First off, we need to add the Helios dependency to our project. We can do it by adding the following block to our build.gradle:

repositories {
      maven { url "https://jitpack.io" }

dependencies {
    compile "com.47deg:helios-core:0.1.0"
    compile "com.47deg:helios-parser:0.1.0"
    compile "com.47deg:helios-optics:0.1.0"

Encoding and Decoding

After adding the dependency, we can start creating our little model:

data class Person(val name: String, val age: Int) {
  companion object

With the @json annotation, we are able to automatically generate encoders and decoders for the Person data class at compile time as follows:

val person = Person("Cristobal", 37)

val jsonFromPerson: Json = with(Person.encoder()) {


You can also write your own encoders and decoders.


We have a simple DSL that takes advantage of the pretty kotlin syntax for creating your own JSON:

import helios.core.Json

val json: Json = JsObject(
"name" to JsString("Simon"),
"age" to JsNumber(26)

Parsing JSON

Of course, we can parse a JSON from an String or a File. Using all of the power from the Arrow library, we’re able to handle parsing errors:

val jsonStr =
     "name": "Cristobal",
     "age": 37

val jsonOrError: Either<Throwable, Json> = Json.parseFromString(jsonStr)

val json : Json = jsonOrError.getOrHandle { JsString("") }

The optics module allows you to query and modify JSON with compile-time safety and without any boilerplate.

import helios.optics.*

Json.path.select("name").string.modify(json, String::toUpperCase)

Note that the code generation will give you an accessor for each JSON field.

Json.path.name.string.modify(json, String::toUpperCase)

Both will produce the same:

 "name": "CRISTOBAL",
 "age": 37


If you want to learn more, please take a look at Helios’ documentation, we also have an examples module that will be helpful.

If you have any questions or comments, feel free to reach out to us on the Helios slack channel or submit an issue to the Helios repository.

This is just the first release of Helios; we have plans for more awesome features like Java time support and other integrations.

The active development of Helios is proudly sponsored by 47 Degrees, a Functional Programming consultancy with a focus on the Scala, Kotlin, and Swift Programming languages.

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