EMR always gives me Class Not Found for Scala app

Question

Hi I wanted to test out the EMR custom step feature.
I created a simple 2 classes Scala application which writes a text file on S3.
Here is the tree

   ├───src
       ├───main
       │   └───scala
       │       └───com
       │           └───myorg
                        -S3Lister.scala
                        -FindMaxDate.scala
       └───test
           └───scala
               └───samples

After building the package with mvn package I submitted it to emr specifying as main class com.myorg.FindMaxDate. However it always gives me this error:
Caused by: java.lang.ClassNotFoundException: scala.Function1
Any Idea what this error could be dued to?
I've used the archetye: net.alchim31.maven:scala-archetype-simple version: 1.6 Thanks

Here is my main class:

object FindMaxDate {

  def main(args : Array[String]) {

    val date_pattern = "\\d{8}".r
    val date_format = new SimpleDateFormat("yyyyMMdd")
    var objectList: List[S3ObjectSummary] = S3Lister.listObjectsInBucket("mycloud-unzipped","sociodemos")

    val sum: scala.collection.immutable.List[Date] = objectList.asScala
                                    .map(file => date_pattern.findFirstIn(file.getKey()))
                                    .map(date => date.getOrElse(null))
                                    .filter(date => date != null)
                                    .map(date => date_format.parse(date)).toList

    S3Lister.writebjectToS3("max_date:" + sum.max + "\n min_date:" + sum.min + "\n",
    "mycloud-source","dates.txt","sociodemos")
  }
}

Here are the Dependencies:

<dependency>
      <groupId>org.scala-lang</groupId>
      <artifactId>scala-library</artifactId>
      <version>${scala.version}</version>
    </dependency>

    <dependency>
      <groupId>com.amazonaws</groupId>
      <artifactId>aws-java-sdk-s3</artifactId>
      <version>1.11.550</version>
    </dependency> ... below there are all the default ones for testing

Answer 1

The most recent version of the EMR at this time (May 2019) is 5.23.0 and it still uses Spark 2.4.0 (https://docs.aws.amazon.com/emr/latest/ReleaseGuide/emr-release-5x.html#emr-5200-release)

https://spark.apache.org/docs/2.4.0/ :

Spark runs on Java 8+, Python 2.7+/3.4+ and R 3.1+. For the Scala API, Spark 2.4.0 uses Scala 2.11. You will need to use a compatible Scala version (2.11.x).

I believe non-experimental support for Scala 2.12.X is only added in Spark 2.4.3, which is not yet available on EMR: https://spark.apache.org/docs/2.4.3/ :

Spark runs on Java 8+, Python 2.7+/3.4+ and R 3.1+. For the Scala API, Spark 2.4.3 uses Scala 2.12. You will need to use a compatible Scala version (2.12.x).