Scala Support

Scala Support

Overview

Scala: http://www.scala-lang.org/

Since Scala’s interoperability with Java is completely unparalleled(*) Scala code can call the Java Application API to build a streaming application. This means a Scala developer can build applications for IBM Streams using Scala code, including Scala anonymous functions and Scala objects for tuples in streams.

Since Scala will call the Java Application API it is recommended to read the getting started guide and take a look at the samples.

(*) http://www.codecommit.com/blog/java/interop-between-java-and-scala

Developing an Application

Just like Java, the Scala application creates a Topology object:

object FizzBuzzScala {
  def main(args: Array[String]) {
  val topology = new Topology("FizzBuzzScala")

This is from the FizzBuzzScala sample application, its full source is here - ADD LINK

Then source streams are created, here a single stream of type TStream[Long] containing integral values is created using a utility method:

var counting = BeaconStreams.longBeacon(topology)

Then functional transformations are applied to the streams to implement the required application analytics, here the stream of numbers is converted to a stream of strings following the rules of FizzBuzz.

var shouts = counting.transform(
   (c:java.lang.Long) => {
       if (c == 0)
            null
       else {
            var shout = ""
            if (c % 3 == 0)
               shout = "Fizz"
            if (c % 5 == 0)
               shout += "Buzz"

            if (shout.isEmpty())
               c.toString()
            else
               shout + "!"
       }
   }  , classOf[String]);

An anonymous function is used to provide the functional transformation, the anonymous function is implicitly converted to the required Java function class (Function<Long,String> in this case). This occurs because the Scala code imports FunctionConversions provided by com.ibm.streamsx.topology/lib/com.ibm.streamsx.topology.jar.

import com.ibm.streamsx.topology.functions.FunctionConversions._;

Note also that the required tuple type (Java's Class<T>) is defined by the Scala expression classOf[String], equivalent to Java's String.class.