How do you exclude fields in Jackson json serialisation (Scala) - json

Question

I am trying to exclude the _passthroughFields property in the example below. When I use the debugger, it looks like my PropertyFilter is never used. What am I doing wrong?
import java.util
import com.fasterxml.jackson.databind.ser.impl.SimpleBeanPropertyFilter.SerializeExceptFilter
import com.fasterxml.jackson.databind.ser.impl.SimpleFilterProvider
import com.fasterxml.jackson.databind.{DeserializationFeature, ObjectMapper, ObjectWriter}
import com.fasterxml.jackson.module.scala.DefaultScalaModule
import com.fasterxml.jackson.module.scala.experimental.ScalaObjectMapper
import org.scalatest.{Matchers, WordSpec}
import scala.collection.immutable.Map
class PassthroughFieldsSpec extends WordSpec with Matchers {
"JacksonParser" when {
"given an Object and undesired fields" should {
"not include those fields in the json response" in {
trait Foo {
def id: String
def _passthroughFields: Map[String, String] = Map.empty
}
class Bar(val id: String, override val _passthroughFields: Map[String, String]) extends Foo
val item = new Bar("abcd", Map.empty)
val mapper = new ObjectMapper() with ScalaObjectMapper
mapper.registerModule(DefaultScalaModule)
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
val excludes = new util.HashSet[String](1)
excludes.add("_passthroughFields")
excludes.add("get_passthroughFields")
val filters = new SimpleFilterProvider()
.addFilter("filter properties by name", new SerializeExceptFilter(excludes))
val writer: ObjectWriter = mapper.writer(filters)
val json = writer.writeValueAsString(item)
json.contains("_passthroughFields") shouldBe false
}
}
}
}

Answer 1

I think you can exclude it using something like #JsonIgnore or make the field transient.
Otherwise if you need to define it outside of the case class code (like in your example) you can do it with Genson.
import com.owlike.genson._
import com.owlike.genson.reflect.VisibilityFilter
// Note that if you use case classes you don't need the visibility filter stuff
// it is used to indicate that private fields should be ser/de
val genson = new GensonBuilder()
.withBundle(ScalaBundle())
.useFields(true, VisibilityFilter.PRIVATE)
.exclude("_passthroughFields")
.create()
genson.toJson(item)
Disclaimer: I am Gensons author.