Scala DataStream&DataStreamUtils accessors fix

[mbalassi]

The PR contains two orthogonal approaches of fixing the access to DataStreamUtils.collect for a scala environment. One or both of the approaches can be merged.

The first simply reexposes access to the underlying java DataStream, while the second effectively adds a scala API for DataStreamUtils.

I am in favor of adding both. Usage of the latter looks as follows:

import org.apache.flink.streaming.api.scala._
import org.apache.flink.contrib.streaming.scala.utils._

object ScalaStreamCollect {

  def main(args: Array[String]) {
    val env = StreamExecutionEnvironment.getExecutionEnvironment

    val it = env.generateSequence(0L, 10L)
      .collect()

    while (it.hasNext){
      print(it.next())
    }
  }
}

At least the first commit should be merged asap as the fix was requested on the user mailing list. [1]

[1] https://mail-archives.apache.org/mod_mbox/flink-user/201602.mbox/%3CCAFqo6nQ24dtExjPOX%3DrSuWSww8skCH23Q8i7CJ3Ef5LYhDj2pA%40mail.gmail.com%3E

[cmonty]

The Scala interface looks good to me and gets rid of the need to call getJavaStream directly.

Thanks!

[brianchhun]

Looks good. It looks like collect is returning a Java iterator instead of a Scala one. Is there a reason for this given that the code is for Scala users?

[mbalassi]

Thanks for the comments. @gumchum: Internally it is stored as a Java Iterator and that is the reason why left it so, but it definitely make sense to convert it to Scala before passing it to the users, so their code does not get "polluted" with Java stuff. I am modifying it.

[StephanEwen]

Looks good to me, but @gumchum's comment is valid.

One more thing, I would call the method on the Scala DataStream def javaStream : JavaStream[T] = stream. I think that is more in line with the Scala style: no parenthesis, because it is a simple accessor, and no "get" prefix, because for methods that appear like variables (no parenthesis), that seems the way they encourage it.

[mbalassi]

Thanks for the comments, updated the PR accordingly.

[StephanEwen]

Thanks, merging this...