Scala Jackson object mapper setting null instead of default values in case class

Question

have a case class Person with default param.

pass mapper a string missing a param, mapper sets it as null.

expecting it to set the default value

why is this ?

example :

@JsonIgnoreProperties(ignoreUnknown = true)
case class Person(id:Int,name:String="")

class MapperTest extends SpecificationWithJUnit {

  "Mapper" should {

     "use default param" in {

        val personWithNoNameString = """{"id":1}"""

        val mapper = new ObjectMapper();
        mapper.registerModule(DefaultScalaModule)
        val personWithNoName = mapper.readValue(personWithNoNameString,classOf[Person])

        personWithNoName.name must be("")
     }
  }
}

get error :

'null' is not the same as ''
java.lang.Exception: 'null' is not the same as ''

Ion Cojocaru · Answer 1 · 2014-10-01T14:44:27.280

2

Jackson mapper is using reflection to set the properties and disregards default values in the case class constructor. There is an open ticket, and it seems that the suggested solution in the comments does not work

case class Person(id:Int,name:String=""){
     def this() = this(0,"")
}

edited Oct 01 '14 at 14:44

answered Oct 01 '14 at 10:13

Ion Cojocaru

2,583
15
16

will not compile (expected Int got null) – Nimrod007 Oct 01 '14 at 11:59
updated the response, null.asInstanceOf[Int] is 0, otherwise use an Option[Int] – Ion Cojocaru Oct 01 '14 at 13:36

score 1 · Answer 2 · answered Apr 19 '19 at 08:46

1

Works with @JsonCreator annotation:

case class Person(id:Int,name:String = ""){
     @JsonCreator
     def this() = this(0,"")
}

answered Apr 19 '19 at 08:46

Vincent

433
3
10

Jodiug · Answer 3 · 2023-07-11T09:15:26.453

0

The above worked for me, but I thought it was less than ideal to define defaults twice. There is another way which also works, avoiding the need for duplicate default declarations.

case class Person(id:Int, name: String = "")

object Person {
  @JsonCreator
  def default = Person(0)
}

edited Jul 11 '23 at 09:15

answered Jul 10 '23 at 15:33

Jodiug

5,425
6
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Scala Jackson object mapper setting null instead of default values in case class

3 Answers3