How to make case classes/objects NOT serializable in scala? annotation/trait/helper works

Question

In scala, I would like to disable the Serializable trait of many case classes, since I want this class of objects to be never serialized and shipped to a remote computer in a distributed computing framework (Specifically Apache Spark), any implementation that does so should trigger an explicit runtime exception when any closure containing it is serialized.

I've tried @transient + null check, it triggers a runtime exception at deserialization (not what I want), and the error information is quite obfuscated. Is there a way to improve this?

Thanks a lot for your advice!

Answer 1

You can implement and mix in a trait that disables serialization:

trait NotSerializable extends Serializable {
  private def writeObject(out: java.io.ObjectOutputStream): Unit = throw new NotSerializableException()
  private def readObject(in: java.io.ObjectInputStream): Unit = throw new NotSerializableException()
  private def readObjectNoData(): Unit = throw new NotSerializableException()
}

case class Test(foo: String) extends NotSerializable

An attempt to serialize will then throw an exception:

new ObjectOutputStream(new ByteArrayOutputStream()).writeObject(Test("test"))
|-> java.io.NotSerializableException: A$A39$A$A39

However, what feature of case class do you actually need? The most simple solution might be to not use case classes and objects.