Arrow Integrations

Λrrow Integrations is part of Λrrow.

Jackson Module

Include arrow-integrations-jackson in your gradle project:

implementation 'io.arrow-kt:arrow-integrations-jackson-module:${version}'

or, using gradle kotlin-dsl.

implementation("io.arrow-kt:arrow-integrations-jackson-module:${version}")

Include arrow-integrations-jackson in your maven project:

<dependency>
  <groupId>io.arrow-kt</groupId>
  <artifactId>arrow-integrations-jackson-module</artifactId>
  <version>${version}</version>
</dependency>

To register support for arrow datatypes, simply call .registerArrowModule() on the object mapper as follows:

import arrow.integrations.jackson.module.registerArrowModule
import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.module.kotlin.registerKotlinModule

val mapper = ObjectMapper()
    .registerKotlinModule()
    .registerArrowModule()

currently supported datatypes:

• Option<T>
• NonEmptyList<T> or Nel<T>
• Either<L, R>
• Validated<E, A>
• Ior<L, R>

Example Usage

Serialization and deserialization of data classes that incorporate arrow data types can be done as follows.

val mapper = ObjectMapper()
  .registerKotlinModule()
  .registerArrowModule()
  .setSerializationInclusion(JsonInclude.Include.NON_ABSENT) // will not serialize None as nulls

data class Organization(val name: String, val address: Option<String>, val websiteUrl: Option<URI>)
data class ArrowUser(val name: String, val emails: NonEmptyList<String>, val organization: Option<Organization>)

val arrowUser = ArrowUser(
  "John Doe",
  nonEmptyListOf(
    "[email protected]", 
    "[email protected]"
  ), 
  Organization("arrow-kt", none(), URI("https://arrow-kt.io").some()).some()
)

mapper.writerWithDefaultPrettyPrinter().writeValueAsString(user)

which serializes as follows.

{
  "name" : "John Doe",
  "emails" : [ "[email protected]", "[email protected]" ],
  "organization" : {
    "name" : "arrow-kt",
    "websiteUrl" : "https://arrow-kt.io"
  }
}

Notice that the Option<T> serializer is configurable via Jackson's serialization inclusion setting. In this example we have configured the serializer to not serialize none() as null, but instead omit it completely.

Various serializers / deserializers within arrow module are configurable. For instance the field names used for serializing / deserializing Either, Validated or Ior can be configured within the registration step:

val mapper: ObjectMapper = ObjectMapper()
  .registerKotlinModule()
  .registerArrowModule(
    eitherModuleConfig = EitherModuleConfig("left", "right"),           // sets the field names for either left / right
    validatedModuleConfig = ValidatedModuleConfig("invalid", "valid"),  // sets the field names for validated invalid / valid
    iorModuleConfig = IorModuleConfig("left", "right")                  // sets the field names for ior left / right
  )
  .setSerializationInclusion(JsonInclude.Include.NON_ABSENT)            // do not serialize None as nulls

More example usages can be found in ExampleTest.kt

Example Usage for Popular Web Frameworks

In real world scenarios Jackson can be installed as the json serialization/deserialization engine. These serializations / deserializations are normally done automatically.

For instance we can customize our mapper with .registerArrowModule() as follows.

object JsonMapper { 
  val mapper: ObjectMapper = ObjectMapper()
    .registerModule(KotlinModule(singletonSupport = SingletonSupport.CANONICALIZE))
    .registerArrowModule()
    .disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
    .disable(JsonParser.Feature.INCLUDE_SOURCE_IN_LOCATION)
    .setSerializationInclusion(JsonInclude.Include.NON_ABSENT)
}

This can then be installed accordingly.

Spring Boot

A way to register of arrow data types JSON serialization / deserialization support in spring boot is as follows:

@Configuration
class JacksonConfiguration {

  @Bean
  @Primary
  fun jsonMapper(): ObjectMapper = JsonMapper.mapper
}

When this bean is registered, the object mapper will be used to deserialize incoming and outgoing JSON payload.

Ktor

Jackson support for arrow data type serialization / deserialization can similarly be registered in Ktor as follows:

install(ContentNegotiation) {
  register(ContentType.Application.Json, JacksonConverter(JsonMapper.mapper))
}