json-files.md

title	type	description	num	previous-page	next-page
How to read and write JSON files?	section	Reading and writing JSON files using UPickle and OSLib	21	json-serialize	json-what-else

{% include markdown.html path="_markdown/install-upickle.md" %}

Read and write raw JSON

To read and write JSON files, you can use uJson and OS-Lib as follows:

{% tabs 'raw' %} {% tab 'Scala 2 and 3' %}

// read a JSON file
val json = ujson.read(os.read(os.pwd / "raw.json"))

// modify the JSON content
json("updated") = "now"

//write to a new file
os.write(os.pwd / "raw-updated.json", ujson.write(json))

{% endtab %} {% endtabs %}

Read and write Scala objects using JSON

To read and write Scala objects to and from JSON files, you can use uPickle and OS-Lib as follows:

{% tabs 'object' class=tabs-scala-version %} {% tab 'Scala 2' %}

import upickle.default._

case class PetOwner(name: String, pets: List[String])
implicit val ownerRw: ReadWriter[PetOwner] = macroRW

// read a PetOwner from a JSON file
val petOwner: PetOwner = read[PetOwner](os.read(os.pwd / "pet-owner.json"))

// create a new PetOwner
val petOwnerUpdated = petOwner.copy(pets = "Toolkitty" :: petOwner.pets)

// write to a new file
os.write(os.pwd / "pet-owner-updated.json", write(petOwnerUpdated))

{% endtab %} {% tab 'Scala 3' %}

import upickle.default.*

case class PetOwner(name: String, pets: List[String]) derives ReadWriter

// read a PetOwner from a JSON file
val petOwner: PetOwner = read[PetOwner](os.read(os.pwd / "pet-owner.json"))

// create a new PetOwner
val petOwnerUpdated = petOwner.copy(pets = "Toolkitty" :: petOwner.pets)

// write to a new file
os.write(os.pwd / "pet-owner-updated.json", write(petOwnerUpdated))

{% endtab %} {% endtabs %}

To serialize and deserialize Scala case classes (or enums) to JSON we need an instance of ReadWriter. To understand how uPickle generates it for you, you can read the How to deserialize JSON to an object? or the How to serialize an object to JSON? tutorials.