Question 109122 in Json Question posted in
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Can't deserialize json with jackson in kotlin

I’ve got a data class:

@JsonIgnoreProperties(ignoreUnknown = true)
data class RouteDetails(
    val name: String,
    val boundingBox: JsonNode,
    val coursePoints: JsonNode
)

That I would like to deserialize a big json payload into (example is abbreviated):

{
  "type": "route",
  "route": {
    "id": 40307258,
    "name": "some bike route",
    "bounding_box": [
      {
        "lat": 3
        "lng": -9
      },
      {
        "lat": 3,
        "lng": -9
      }
    ],
    "course_points": [
      {...}
    ]
  }
}

And it seems like this should be a straight forward deserialization from what I can tell:

val objectMapper = ObjectMapper()
return objectMapper.readValue(response, RouteDetails::class.java)

But when I actually try this I get an error:
error

cannot deserialize from Object value (no delegate- or property-based Creator)

I’ve looked up examples and the documentation and I can’t tell what I’m doing wrong. I have a data class, I have the annotation to ignore the properties. Not seeing what I’m missing. Any help??

Tags:

3

Answers


  1. 0

    Observed some of the following issues with json modelling in OP.

    1. boundingBox: JsonNode and coursePoints: JsonNode is JsonNode but in json it is an array,
    2. course_points json does not contain any specific data type so assumed here as an empty array of type Any.
    3. I assume OP need to exclude id from the json, so added in json but not in DTO.

    I have modelled data class for the json mentioned in OP as below

    data class BoundingBox(
  val lat: Int,
  val lng: Int
)

data class Route(
  @JsonProperty("bounding_box")
  val boundingBox: List<BoundingBox>,
  @JsonProperty("course_points")
  val coursePoints: List<Any>?,
  // val id: Int, // need to skip while reading/writing to json str
  val name: String
)

@JsonIgnoreProperties(ignoreUnknown = true)
data class RouteDetails(
  val route: Route,
  val type: String
)

    Response json:
    Added additional property "someExtraKeys": "withExtraValue", to demonstrate that it is getting dropped while serialisation/deserialisation due to @JsonIgnoreProperties(ignoreUnknown = true)

    val response =
"""
  {
  "type": "route",
  "someExtraKeys": "withExtraValue",
  "route": {
    "id": 40307258,
    "name": "some bike route",
    "bounding_box": [
      {
        "lat": 3,
        "lng": -9
      },
      {
        "lat": 3,
        "lng": -9
      }
    ],
    "course_points": []
  }
}
""".trimIndent()

    Client code:

    val jacksonObjectMapper = jacksonObjectMapper()
jacksonObjectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
val readValue = jacksonObjectMapper.readValue(response, RouteDetails::class.java)
println(jacksonObjectMapper.writeValueAsString(readValue))    
/*
{
  "route": {
    "bounding_box": [
      {
        "lat": 3,
        "lng": -9
      },
      {
        "lat": 3,
        "lng": -9
      }
    ],
    "course_points": [],
    "name": "some bike route"
  },
  "type": "route"
}
*/
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  2. 0

    Try adding the jackson-module-kotlin, this error means that Jackson can’t figure out how to use your constructor/"creator" (which it can’t by default for Kotlin data classes)

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  3. 0

    Your JSON payload does not match the data model.

    What you showed is a JSON object that has a "route" object. So you need to model a data class that has a RouteDetail:

    data class Response(
    val type: String
    val route: RouteDetails
)

    Then you would parse the top-level object and get the route from there:

    val objectMapper = ObjectMapper()
val response = objectMapper.readValue(response, Response::class.java)
return response.route
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