Working with JSON

Json values are supported through codecs, which encode/decode values to json strings. Most often, you’ll be using a third-party library to perform the actual json parsing/printing. Currently, zio-json, Circe, µPickle, Spray JSON, Play JSON, Tethys JSON, Jsoniter-scala, and Json4s are supported.

All of the integrations, when imported into scope, define a jsonBody[T] method. This method depends on library-specific implicits being in scope, and derives from them a json codec. The derivation also requires implicit Schema[T] and Validator[T] instances, which should be automatically derived. For more details see documentation on supporting custom types.

If you have a custom, implicit Codec[String, T, Json] instance, you should use the customJsonBody[T] method instead. This description of endpoint input/output, instead of deriving a codec basing on other library-specific implicits, uses the json codec that is in scope.

Circe

To use Circe, add the following dependency to your project:

"com.softwaremill.sttp.tapir" %% "tapir-json-circe" % "0.20.0-M4"

Next, import the package (or extend the TapirJsonCirce trait, see MyTapir):

import sttp.tapir.json.circe._

This will allow automatically deriving Codecs which, given an in-scope circe Encoder/Decoder and a Schema, will create a codec using the json media type. Circe includes a couple of approaches to generating encoders/decoders (manual, semi-auto and auto), so you may choose whatever suits you.

Note that when using Circe’s auto derivation, any encoders/decoders for custom types must be in scope as well.

Additionally, the above import brings into scope the jsonBody[T] body input/output description, which uses the above codec.

For example, to automatically generate a JSON codec for a case class:

import sttp.tapir._
import sttp.tapir.json.circe._
import sttp.tapir.generic.auto._
import io.circe.generic.auto._

case class Book(author: String, title: String, year: Int)

val bookInput: EndpointIO[Book] = jsonBody[Book]

Circe lets you select an instance of io.circe.Printer to configure the way JSON objects are rendered. By default Tapir uses Printer.nospaces, which would render:

import io.circe._

Json.obj(
  "key1" -> Json.fromString("present"),
  "key2" -> Json.Null
)

as

{"key1":"present","key2":null}

Suppose we would instead want to omit null-values from the object and pretty-print it. You can configure this by overriding the jsonPrinter in tapir.circe.json.TapirJsonCirce:

import sttp.tapir.json.circe._
import io.circe.Printer

object MyTapirJsonCirce extends TapirJsonCirce {
  override def jsonPrinter: Printer = Printer.spaces2.copy(dropNullValues = true)
}

import MyTapirJsonCirce._

Now the above JSON object will render as

{"key1":"present"}

µPickle

To use µPickle add the following dependency to your project:

"com.softwaremill.sttp.tapir" %% "tapir-json-upickle" % "0.20.0-M4"

Next, import the package (or extend the TapirJsonuPickle trait, see MyTapir and add TapirJsonuPickle not TapirCirceJson):

import sttp.tapir.json.upickle._

µPickle requires a ReadWriter in scope for each type you want to serialize. In order to provide one use the macroRW macro in the companion object as follows:

import sttp.tapir._
import sttp.tapir.generic.auto._
import upickle.default._
import sttp.tapir.json.upickle._

case class Book(author: String, title: String, year: Int)

object Book {
  implicit val rw: ReadWriter[Book] = macroRW
}

val bookInput: EndpointIO[Book] = jsonBody[Book]

Like Circe, µPickle allows you to control the rendered json output. Please see the Custom Configuration of the manual for details.

For more examples, including making a custom encoder/decoder, see TapirJsonuPickleTests.scala

Play JSON

To use Play JSON add the following dependency to your project:

"com.softwaremill.sttp.tapir" %% "tapir-json-play" % "0.20.0-M4"

Next, import the package (or extend the TapirJsonPlay trait, see MyTapir and add TapirJsonPlay not TapirCirceJson):

import sttp.tapir.json.play._

Play JSON requires Reads and Writes implicit values in scope for each type you want to serialize.

Spray JSON

To use Spray JSON add the following dependency to your project:

"com.softwaremill.sttp.tapir" %% "tapir-json-spray" % "0.20.0-M4"

Next, import the package (or extend the TapirJsonSpray trait, see MyTapir and add TapirJsonSpray not TapirCirceJson):

import sttp.tapir.json.spray._

Spray JSON requires a JsonFormat implicit value in scope for each type you want to serialize.

Tethys JSON

To use Tethys JSON add the following dependency to your project:

"com.softwaremill.sttp.tapir" %% "tapir-json-tethys" % "0.20.0-M4"

Next, import the package (or extend the TapirJsonTethys trait, see MyTapir and add TapirJsonTethys not TapirCirceJson):

import sttp.tapir.json.tethysjson._

Tethys JSON requires JsonReader and JsonWriter implicit values in scope for each type you want to serialize.

Jsoniter Scala

To use Jsoniter-scala add the following dependency to your project:

"com.softwaremill.sttp.tapir" %% "tapir-jsoniter-scala" % "0.20.0-M4"

Next, import the package (or extend the TapirJsonJsoniter trait, see MyTapir and add TapirJsonJsoniter not TapirCirceJson):

import sttp.tapir.json.jsoniter._

Jsoniter Scala requires JsonValueCodec implicit value in scope for each type you want to serialize.

Json4s

To use json4s add the following dependencies to your project:

"com.softwaremill.sttp.tapir" %% "tapir-json-json4s" % "0.20.0-M4"

And one of the implementations:

"org.json4s" %% "json4s-native" % "4.0.3"
// Or
"org.json4s" %% "json4s-jackson" % "4.0.3"

Next, import the package (or extend the TapirJson4s trait, see MyTapir and add TapirJson4s instead of TapirCirceJson):

import sttp.tapir.json.json4s._

Json4s requires Serialization and Formats implicit values in scope, for example:

import org.json4s._
// ...
implicit val serialization: Serialization = org.json4s.jackson.Serialization
implicit val formats: Formats = org.json4s.jackson.Serialization.formats(NoTypeHints)

Zio JSON

To use Zio JSON, add the following dependency to your project:

"com.softwaremill.sttp.tapir" %% "tapir-json-zio" % "0.20.0-M4"

Next, import the package (or extend the TapirJsonZio trait, see MyTapir and add TapirJsonZio instead of TapirCirceJson):

import sttp.tapir.json.zio._

Zio JSON requires JsonEncoder and JsonDecoder implicit values in scope for each type you want to serialize.

Other JSON libraries

To add support for additional JSON libraries, see the sources for the Circe codec (which is just a couple of lines of code).

Schemas

To derive json codecs automatically, not only implicits from the base library are needed (e.g. a circe Encoder/Decoder), but also an implicit Schema[T] value, which provides a mapping between a type T and its schema. A schema-for value contains a single schema: Schema field.

See custom types for details.

Next

Read on about working with forms.