Custom Jackson deserializer registered with the mapper

JacksonRegisteredSerializers.scala

package us.aharon.test.json

import com.fasterxml.jackson.annotation.JsonProperty
import com.fasterxml.jackson.core.JsonParser
import com.fasterxml.jackson.databind.{DeserializationContext, JsonDeserializer, JsonNode}
import com.fasterxml.jackson.databind.json.JsonMapper
import com.fasterxml.jackson.databind.module.SimpleModule
import com.fasterxml.jackson.module.scala.DefaultScalaModule

object JacksonRegisteredSerializers extends App {

  /**
   * Custom Jackson deserializer for BigInt.
   *
   * Expects [[BigInt]] in JSON as a [[String]].
   * {{{
   * {
   *   "a_big_int": "123456789123456789"
   * }
   * }}}
   */
  private class BigIntDeserializer extends JsonDeserializer[BigInt] {
    override def deserialize(p: JsonParser, ctxt: DeserializationContext): BigInt = {
      val node: JsonNode = p.getCodec.readTree(p)
      BigInt(node.asText)
    }
  }

  // Define a module for the custom deserializer.
  val bigIntModule = new SimpleModule()
    .addDeserializer(classOf[BigInt], new BigIntDeserializer())
  val mapper = JsonMapper.builder()
    .addModule(DefaultScalaModule) // Register the module with the mapper.
    .addModule(bigIntModule)
    .build()

  /**
   * Our example object as a target for deserialization.
   */
  case class ExampleObj(
    @JsonProperty("a_big_int")
    val aBigInt: BigInt
  )

  val example =
    """
      |{
      |  "a_big_int": "123456789123456789"
      |}
      |""".stripMargin

  // Deserialize
  val actual = mapper.readValue(example, classOf[ExampleObj])

  val expected = ExampleObj(BigInt("123456789123456789"))

  println(s"Deserialized ExampleObj:  $actual")
  assert(actual == expected)
}