When working with UUIDs in Scala using json4s, you might run into issues serializing and deserializing UUID objects by default. Json4s does not handle java.util.UUID out-of-the-box. Fortunately, there’s a simple and elegant solution using JavaTypesSerializers.

To enable UUID support in json4s, you can add JavaTypesSerializers.all to your implicit formats:

implicit lazy val formats: Formats = 
  Serialization.formats(NoTypeHints) ++ JavaTypesSerializers.all

val user = User(UUID.randomUUID(), "John Doe")
val jsonString = Serialization.write(user)
println(jsonString)

When working with Java types like UUID, JavaTypesSerializers.all is the most straightforward way to extend Json4s support. It’s a clean, idiomatic, and minimal solution — no need to write custom serializers manually.

Why formats Are Needed in Json4s?

In json4s, formats are essential because they tell the library how to convert between Scala objects and JSON — this includes:

• Serialization (object → JSON)
• Deserialization (JSON → object)

Formats includes Type hints, Custom serializers (e.g., for UUID, Date, etc.) and Information on how to map case class fields

Without formats, json4s doesn’t know how to handle non-primitive types.