gzoller / scalajack Edit

Fast JSON parser/generator for Scala

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license Maven Central

ScalaJack 7 is an all-new ScalaJack implmenation built on Scala 3. For Scala 2.13 ScalaJack, please use (frozen) version 6.2.0. ScalaJack 7 is built on JDK 13+.

ScalaJack is a very fast, seamless serialization engine for JSON, and other protocols, designed to require the minimum amount of help possible when serializing a class.

Advanced Features:

  • Handles tuples
  • 'Any' support
  • Handles default values for case class fields
  • Rich configuration of trait type hint/value
  • Supports value classes
  • Sealed trait-style enumerations
  • Extensible to other encodings (JSON, CSV, MongoDB, and DynamoDB are provided by ScalaJack, but you can roll your own too!)


ScalaJack is extremely simple to use.

Include the following in your build.sbt:

    libraryDependencies ++= Seq("co.blocke" %% "scalajack" % SJ_VERSION)

To use the highly-recommended reflection compiler plug-in, add to build.sbt:

addCompilerPlugin("co.blocke" %% "scala-reflection" % VERSION)

where VERSION is the latest scala-reflection version found by looking at the 'maven central' badge from this repo: www.blocke.co/scala-reflection

If you want to use the optional MongoDB serialization support include this as well:

    libraryDependencies ++= Seq("co.blocke" %% "scalajack_mongo" % SJ_VERSION)

DynamoDB helpers are available here:

    libraryDependencies ++= Seq("co.blocke" %% "scalajack_dynamo" % SJ_VERSION)

where SJ_VERSION is this version of ScalaJack (see 'maven central' badge of this repo).

Now you're good to go! Let's use ScalaJack in your project to serialize/de-serialize a case class object into JSON:

import co.blocke.scalajack._

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

val sj = ScalaJack()
val js = sj.render(Person("Mike",34))  // js == """{"name":"Mike","age":34}"""
val inst = sj.read[Person](js) // re-constitutes original Person

Couldn't be simpler!

A word about performance...

Compared to pre-7.0 ScalaJack, which used Scala 2.x runtime reflection, ScalaJack is up to 30% faster in many cases when used with the highly-recommended scala-reflection compiler plugin.

A word about macros...

ScalaJack 7 uses Scala 3 macros to the fullest extent possible to do the hard work of reflecting on types. Macros impact the compile/test cycle in ways that are non-intuitive at first. Think of this example:

// File1.scala
case  class  Foo(name: String)

// File2.scala
val  js = sj.read[Foo](someJson)

In a non-macro implementation (e.g. Scala 2 runtime reflection) if you update Foo in File1.scala you naturally expect sbt to re-compile this file, and anything that depends on Foo, and the changes will be picked up in your program, and all will be well.

That's not necessarily what happens with macros! Remember, the macro code is run at compile-time. File2.scala needs to be re-compiled because the macro needs to be re-run to pick up your changes to Foo class in File1.scala. Unfortunately sbt doesn't pick up this dependency! If you don't know any better you'll just re-run your program after a change to File1.scala, like normal, and get a spectacular exception with exotic errors that won't mean much to you. The solution is you need to also recompile File2.scala.

This means you will be doing more re-compiling with macro-based code than you would without the macros. It's an unfortunate cost of inconvenience and time, but the payoff is a dramatic gain in speed at runtime, and in the case of reflection in Scala 3, using macros is really the only way to accomplish reflection.


Non-JSON Formats:


  • 7.0.1 -- GA release of ScalaJack 7 for Scala 3.
  • 7.0.0-M2 -- Initial release for Scala 3