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json-binders is a library for Scala/Scala.js that allows you to serialize/deserialize Scala case classes, primitive types to/from JSON representation.

Why json-binders?

There already exists a numerous libraries for the same purpose, like scala/pickling, upickle, spray-json targeting Scala and FasterXML/jackson, gson and many others Java libraries that you may use in Scala.

Key features of json-binders are:

  1. Compile-time code generation without runtime reflection
  2. Streaming/iterative underlying API
  3. Clean/interoperable JSON format
  4. Schemaless fields support
  5. Scala.js support

The most close alternative is a uPickle, and the most notable differences that json-binders gives you are:

  1. 2-3 times performance boost, see below on performance benchmark
  2. ability to work with schemaless fields (Value type)
  3. FasterXML/jackson dependency for JVM compilation instead of Jaws that is used by uPickle
  4. uPickle serializes Option[Something] as array, while in json-binders it's serialized as a regular field.


Add to project with SBT: "com.hypertino" %% "json-binders" % "1.0-SNAPSHOT"


A plain example on how-to start using a library:

case class Crocodile(
  name: String,
  length: Int,
  color: Option[String]

import com.hypertino.binders.json.JsonBinders._

val crocodileJson = Crocodile("Gena", 250, Some("Green")).toJson

// crocodileJson: String = {"name":"Gena","length":250,"color":"Green"}

val crocodile = crocodileJson.parseJson[Crocodile]

That's it. If you work with string representation of JSON then you only have to use toJson/parseJson macro calls.

Supported types

Primitive types

json-binders supports primitive types: Int, Long, Double, Float, BigDecimal and Boolean with String.

Please note that Long range is limited due to fact that Javascript's Number type (64 bit IEEE 754) only has about 53 bits of precision

Duration and FiniteDuration

Duration and FiniteDuration are supported out of box. Duration is serialized as a string value and FiniteDuration as a numeric value in milliseconds.

Case-classes and normal classes/traits with companion object

As it shown in an example the case-classes are supported out of box. Any regular class or a trait that have a companion object with corresponding apply/unaply methods are supported as well.

Default case class values

Case-classes can have default values specified on fields. And json-binders will return default field value in case if JSON source doesn't contains that field or the value of the field is null.

case class Zoo(
  name: String,
  open: Boolean = true

val zoo = """{"name":"Moscow Zoo"}""".parseJson[Zoo]
// is true here

Case-class field names

If you need a special name on some field, you may set it with an attribute fieldName: Example:

case class Kid(
  @fieldName("name of kid") name: String, 
  age: Int

Kid("John", 13).toJson // produces: {"name of kid":"John","age":13}


You can read and write almost any Scala collection class.

List(1,2,3).toJson // produces `[1,2,3]` 

"[1,2,3]".parseJson[List[Int]] // produces List[Int] = List(1, 2, 3) 

// more complex case:
List(Kid("John", 13), Kid("Anthony", 12), Kid("Ellie", 13)).toJson

All collection items have to be bindable (primitive or a case-class or collection, etc). In general any collection that implements canBuildFrom is supported.

Map[String, Something]

Map[String, Something] is a special case and it is serialized as a JSON object. The Something here can be any bindable type.

null handling

If a field is defined as Option[Something] then null value is deserialized as None and vice versa.

If a field can't be null, like Int or any other primitive value, an exception will be thrown while reading null value.


json-binders tries to find best matching data type when reading Either[_,_]

"1".parseJson[Either[Int,String]] // returns Left(1)

More complex scenarios are possible with collections and objects.

Custom types

You may support any custom type implementing ImplicitSerializer and ImplicitDeserializer traits.


class InstantTypeSerializer extends ImplicitSerializer[Instant, JsonSerializer[_]] {
  override def write(serializer: JsonSerializer[_], value: Instant): Unit = serializer.writeLong(value.toEpochMilli)

class InstantTypeDeserializer extends ImplicitDeserializer[Instant, JsonDeserializer[_]] {
  override def read(deserializer: JsonDeserializer[_]): Instant = Instant.ofEpochMilli(deserializer.readLong())

object InstantJsonBinders {
  implicit val serializer = new InstantTypeSerializer
  implicit val deserializer = new InstantTypeDeserializer

import JsonBinders._
import InstantJsonBinders._

val instantJson = Instant.parse("2016-10-01T00:12:42.007Z").toJson
// instantJson: String = 1475280762007

val instant = instantJson.parseJson[Instant]
// instant: org.threeten.bp.Instant = 2016-10-01T00:12:42.007Z

Schemaless/custom fields

binders library provides a Value type that:

  • Implements the scala.Dynamic to access object fields using dynamic invocation
  • Can be a Null, Obj, Lst, Text, Number or Bool
  • Guarantees that it's serializable to JSON
  • Provides a visitor pattern interface to Value tree

One of the examples of using Value is when you need some custom, schema-free data inside some class. Example:

import com.hypertino.binders.value._

case class Crocodile(
  name: String,
  color: Option[String],
  extra: Value          // <- custom extra data stored here

import com.hypertino.binders.json.JsonBinders._

val crocodileJson = Crocodile("Gena", Some("Green"), 
  Obj.from("country" -> "Russia", "age" -> 49) // this constructs Obj type for extra field

// crocodileJson: String = {"name":"Gena","color":"Green","extra":{"country":"Russia","age":49}}

val crocodile = crocodileJson.parseJson[Crocodile]

val country = // accessing field through `scala.Dynamic` 

val age = crocodile.extra.age // returned type is `Value` instance type `Number`


Benchmark results here are gathered on Macbook Pro Core i5 2.5GHz. I'm comparing json-binders with uPickle 0.4.1.

JVM benchmark

JVM benchmark is done with OpenJDK jmh tool. To validate results run sbt 'benchTestJVM/jmh:run'

JsonBindersBenchmark.Binders_deserializeCaseClass                       thrpt  200   610167,407 ± 4217,269  ops/s
JsonBindersBenchmark.Binders_deserializeCaseClass2                      thrpt  200    46471,465 ±  299,064  ops/s
JsonBindersBenchmark.Binders_serializeAndDeserializeCaseClass           thrpt  200   306330,001 ± 2027,039  ops/s
JsonBindersBenchmark.Binders_serializeAndDeserializeCaseClass2          thrpt  200    31640,815 ±  165,431  ops/s
JsonBindersBenchmark.Binders_serializeAndDeserializeCaseClass2NoOption  thrpt  200    25878,555 ±  128,021  ops/s
JsonBindersBenchmark.Binders_serializeCaseClass                         thrpt  200  1082355,813 ± 5263,266  ops/s
JsonBindersBenchmark.Binders_serializeCaseClass2                        thrpt  200   103028,012 ±  441,978  ops/s

JsonBindersBenchmark.Upickle_deserializeCaseClass                       thrpt  200   203965,085 ± 1693,887  ops/s
JsonBindersBenchmark.Upickle_deserializeCaseClass2                      thrpt  200    22248,249 ±  282,005  ops/s
JsonBindersBenchmark.Upickle_serializeAndDeserializeCaseClass           thrpt  200   111382,834 ±  542,432  ops/s
JsonBindersBenchmark.Upickle_serializeAndDeserializeCaseClass2          thrpt  200    13816,731 ±  123,517  ops/s
JsonBindersBenchmark.Upickle_serializeAndDeserializeCaseClass2NoOption  thrpt  200    15366,293 ±  161,253  ops/s
JsonBindersBenchmark.Upickle_serializeCaseClass                         thrpt  200   410833,045 ± 2858,354  ops/s
JsonBindersBenchmark.Upickle_serializeCaseClass2                        thrpt  200    40894,468 ±  245,502  ops/s

JS benchmark

JS benchmark is more naive and straitforward. It's done with node v6.3.0 and fullOptJS option enabled. To execute benchmark run sbt 'benchTestJS/run'

Binders_serializeCaseClass                             299001.4286 ops/sec. 2093010 cnt for 7000 ms
Binders_deserializeCaseClass                            26036.4205 ops/sec. 183010 cnt for 7029 ms
Binders_serializeAndDeserializeCaseClass                21526.7284 ops/sec. 151010 cnt for 7015 ms
Binders_serializeCaseClass2                             27178.4291 ops/sec. 191010 cnt for 7028 ms
Binders_deserializeCaseClass2                            2473.9011 ops/sec. 18010 cnt for 7280 ms
Binders_serializeAndDeserializeCaseClass2                2220.2191 ops/sec. 16010 cnt for 7211 ms
Binders_serializeAndDeserializeCaseClass2NoOption        1710.0055 ops/sec. 12442 cnt for 7276 ms

Upickle_serializeCaseClass                              35537.3198 ops/sec. 249010 cnt for 7007 ms
Upickle_deserializeCaseClass                            20819.9059 ops/sec. 146010 cnt for 7013 ms
Upickle_serializeAndDeserializeCaseClass                11695.6646 ops/sec. 82010 cnt for 7012 ms
Upickle_serializeCaseClass2                              4985.0491 ops/sec. 35010 cnt for 7023 ms
Upickle_deserializeCaseClass2                            2419.2860 ops/sec. 17010 cnt for 7031 ms
Upickle_serializeAndDeserializeCaseClass2                1610.0759 ops/sec. 11665 cnt for 7245 ms
Upickle_serializeAndDeserializeCaseClass2NoOption        2022.3135 ops/sec. 14773 cnt for 7305 ms

Additional serializers

soc-time is a Scala.JS compatible Java8 time implementation.

Add to project with SBT: "com.hypertino" %% "json-time-binders" % "1.0-SNAPSHOT". See an example in TestInstantSerializer.scala

Things to cover

  • naming convention converters;
  • stream API;
  • iterator/stream/seq shortcomings;


json-binders is licensed under BSD 3-clause as stated in file LICENSE