Trait that is not serializable

Question

I'd like to disable the serialization of a trait, so that all the classes that extends this trait will fail on serialization.

How can I achieve this in Scala?

I'm using spark, and I need this because the class will be very big, and serializing it will induce a performance hit, so I'd like to prevent it being serialized by mistake.

Answer 1

Here is my solution:

trait NonSerializable extends java.io.Externalizable {

  def writeExternal(out: java.io.ObjectOutput): Unit = {
    throw new UnsupportedOperationException(getClass() + " is not Serializable")
  }

  def readExternal(in: java.io.ObjectInput): Unit = {
    throw new UnsupportedOperationException(getClass() + " is not Serializable")
  }
}

case class Foo(s: String) extends NonSerializable {
}

object Foo extends App {
  val bytes = new java.io.ByteArrayOutputStream
  val out = new java.io.ObjectOutputStream(bytes)
  out.writeObject(Foo("bar"))
}

Use Externalizable to inject an exception in serialization. Subclass should not override readExternal or writeExternal .

Note: NonSerializable violates the contract of Serializable . I'm not sure if it can work with other libraries based on the contract of Serializable .