无法使用 gson 将 json 反序列化为案例 class

Question

I am working in Scala programming language and want to deserialize json to case class

My case class looks like this

case class Events
(
  Name: String,
  Field1: Option[Seq[String]],
  Field2: Option[Seq[String]],
  Field3: Option[Seq[String]]
)

case class RootInterface
(
  Events: Seq[Events]
)

The json looks like this

"Events": [
    {
      "Name": "event1",
      "Field1": ["f1"]
    },
    {
      "Name": "event2",
      "Field1": ["f1","f2"]
    }
  ]

And the code I have to do this is

val gson = new Gson

gson.fromJson(json, classOf[RootInterface])

when I try to do this I get the below error

java.lang.RuntimeException: Unable to invoke no-args constructor for scala.collection.Seq<***.Events>. Register an InstanceCreator with Gson for this type may fix this problem.

Ho can I fix this?

Answer 1

You won't be able to us Java libraries expecting Java Beans with a standard case classes

• you don't have no-artgs constructor (you would have to create a default constructor)
• you have only setters (you didn't use var s)
• and accessors don't use Bean syntax (you would have to use @BeanProperty )

So you would have to use something like:

case class Events(
  @BeanProperty var name: String,
  @BeanProperty var field1: Option[Seq[String]],
  @BeanProperty var field2: Option[Seq[String]],
  @BeanProperty var field3: Option[Seq[String]]
) {

  def this() = this("", None, None, None)
}

but this means that library uses runtime reflection, which throws type safety under the bus. Personally, I see no reason to use Java JSON libraries provided you have a choice, because I have a compile time reflection in Scala libraries.