В отражении Scala TypeTag обычно может быть создан из Type с помощью TypeCreator:
object TypeUtils {
import ScalaReflection.universe._
def createTypeTag[T](
tpe: Type,
mirror: reflect.api.Mirror[reflect.runtime.universe.type]
): TypeTag[T] = {
TypeTag.apply(
mirror,
NaiveTypeCreator(tpe)
)
}
case class NaiveTypeCreator(tpe: Type) extends reflect.api.TypeCreator {
def apply[U <: reflect.api.Universe with Singleton](
m: reflect.api.Mirror[U]): U#Type = {
// assert(m eq mirror, s"TypeTag[$tpe] defined in $mirror cannot be migrated to $m.")
tpe.asInstanceOf[U#Type]
}
}
К сожалению, оказывается, что вывод createTypeTag
не сериализуем, в отличие от typeTag, созданного на основе вывода во время компиляции:
import java.io.{ByteArrayOutputStream, ObjectOutputStream}
import org.apache.spark.sql.catalyst.ScalaReflection
import org.scalatest.FunSpec
class TypeTagFromType extends FunSpec {
import ScalaReflection.universe._
it("create TypeTag from reflection") {
val ttg = typeTag[String]
val ttg2 = TypeUtils.createTypeTag(ttg.tpe, ttg.mirror)
Seq(
ttg -> "from static inference",
ttg2 -> "from dynamic type"
).foreach {
case (tt, k) =>
println(k)
val bos = new ByteArrayOutputStream()
try {
val out = new ObjectOutputStream(bos)
out.writeObject(tt)
out.flush()
val array = bos.toByteArray
} finally {
bos.close()
}
}
}
}
Это дает результат:
from static inference
from dynamic type
scala.reflect.runtime.JavaMirrors$JavaMirror$$anon$2
java.io.NotSerializableException: scala.reflect.runtime.JavaMirrors$JavaMirror$$anon$2
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1184)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
Указывает, что второй TypeTag не является сериализуемым, а первый — сериализуемым.
Итак, мой вопрос: как сделать второй TypeTag сериализуемым, как первый?
На данный момент я использую scala 2.12.10.