I am trying to create a custom Aggregator function producing a Map as the result, however it requires an Encoders. As referenced in https://spark.apache.org/docs/2.1.0/api/java/org/apache/spark/sql/Encoders.html, there isn't one for now.
Does anyone know a workaround for this? Thank you in advance!
This is not exactly an answer, but if someone came here with the same question but in Scala instead of Java, they can use the ExpressionEncoder:
import org.apache.spark.sql.catalyst.encoders.ExpressionEncoder
// ...
def outputEncoder: Encoder[Map[String, Int]] = ExpressionEncoder()
For the original question in Java, this link about how to write a custom encoder might help.