JSON Codecs

Introduction

JSON (JavaScript Object Notation) is a widely used data interchange format for transmitting and storing data. ZIO Schema provides zio-schema-json module which has functionality to derive JSON codecs from a ZIO Schema. JSON codecs allow us to easily serialize and deserialize data in JSON format. In this article, we will explore how derive JSON codecs using the ZIO Schema.

Installation

To derive JSON codecs from a ZIO Schema, we need to add the following dependency to our build.sbt file:

libraryDependencies += "dev.zio" %% "zio-schema-json" % 1.5.0

JsonCodec

The JsonCodec object inside the zio.schema.codec package provides the jsonCodec operator which allows us to derive JSON codecs from a ZIO Schema:

object JsonCodec {
  def jsonCodec[A](schema: Schema[A]): zio.json.JsonCodec[A] = ???
}

Let's try an example to see how it works:

import zio._
import zio.json._
import zio.schema.{DeriveSchema, Schema}

case class Person(name: String, age: Int)

object Person {
  implicit val schema: Schema[Person] =
    DeriveSchema.gen
  implicit val jsonCodec: zio.json.JsonCodec[Person] =
    zio.schema.codec.JsonCodec.jsonCodec(schema)
}

object Main extends ZIOAppDefault {
  def run = for {
    _ <- ZIO.debug("JSON Codec Example:")
    person: Person  = Person("John", 42)
    encoded: String = person.toJson
    _       <- ZIO.debug(s"person object encoded to JSON string: $encoded")
    decoded <- ZIO.fromEither(Person.jsonCodec.decodeJson(encoded))
    _       <- ZIO.debug(s"JSON object decoded to Person class: $decoded")
  } yield ()
}

BinaryCodec

We can also derive a binary codec from a ZIO Schema using the schemaBasedBinaryCodec:

object JsonCodec {
  implicit def schemaBasedBinaryCodec[A](implicit schema: Schema[A]): BinaryCodec[A] = ???
}

Let's try an example:

import zio._
import zio.schema.codec.BinaryCodec
import zio.schema.{DeriveSchema, Schema}

case class Person(name: String, age: Int)

object Person {
  implicit val schema: Schema[Person] =
    DeriveSchema.gen
  implicit val jsonBinaryCodec: BinaryCodec[Person] =
    zio.schema.codec.JsonCodec.schemaBasedBinaryCodec(schema)
}

object Main extends ZIOAppDefault {
  def run = for {
    _ <- ZIO.debug("JSON Codec Example:")
    person: Person = Person("John", 42)
    encoded: Chunk[Byte] = Person.jsonBinaryCodec.encode(person)
    _ <- ZIO.debug(s"person object encoded to Binary JSON: ${toHex(encoded)}")
    decoded <- ZIO.fromEither(Person.jsonBinaryCodec.decode(encoded))
    _ <- ZIO.debug(s"JSON object decoded to Person class: $decoded")
  } yield ()

  def toHex(bytes: Chunk[Byte]): String =
    bytes.map("%02x".format(_)).mkString(" ")
}

The output of the above program is:

JSON Codec Example:
person object encoded to JSON string: 7b 22 6e 61 6d 65 22 3a 22 4a 6f 68 6e 22 2c 22 61 67 65 22 3a 34 32 7d
JSON object decoded to Person class: Person(John,42)

By utilizing JSON codecs derived from ZIO Schema, developers can easily serialize and deserialize data in JSON format without writing boilerplate code. This enhances productivity and simplifies data handling in Scala applications.