learning kafka streams with scala
TRANSCRIPT
Learning Kafka Streams with Scala
Himanshu GuptaLead ConsultantKnoldus Software LLP
Img src - http://danlebrero.com/2017/01/05/proof-of-concept-using-kafkastreams-and-ktables/
Agenda
● What is Kafka Streams?● Why do we need to implement it in Scala?● Challenge● Solution● Examples of Kafka Streams with Scala● Demo
What is Kafka Streams?
The easiest way to write mission-critical real-time applications and microservices with all the benefits of Kafka's server-side cluster
technology
● Write standard Java applications.
● No separate processing cluster required
● Elastic, highly scalable, fault-tolerant
● Equally viable for small, medium, & large use cases
● Exactly-once processing semantics
● Develop on Mac, Linux, Windows
● Deploy to containers, VM(s), bare metal, cloud
● Fully integrated with Kafka security
Key Features
Where we can use it?
Img src - https://kafka.apache.org/documentation/streams/
Example
object WordCountApplication { def main(args: Array[String]) { val textLines: KStream[String, String] = builder.stream("TextLinesTopic") val wordCounts: KTable[String, Long] = textLines .flatMapValues(textLine => textLine.toLowerCase.split("\\W+").toIterable.asJava) .groupBy((_, word) => word) .count("Counts") wordCounts.to(Serdes.String(), Serdes.Long(), "WordsWithCountsTopic") val streams: KafkaStreams = new KafkaStreams(builder, config) streams.start() } }
Why do we need to implement it in Scala?
● To provide a functional solution to a problem.
● To get better concurrency model.
● To write succinct and concise code.
● To have type safety or static typing.
Challenge
No Scala API
Challenge
No Scala API
Is it really a challenge?
Challenge
No Scala API
Is it really a challenge?
Yes
Challenge
No Scala API
Is it really a challenge?
Yes
Because Scala does not accept a function literal as a valid expression for any Single Abstract Method (SAM) type
Example
Scala functions don’t implement the Runnable and Callable interfaces even though there’s a simply mapping.
val r: Runnable = () => println("Run!")
error: type mismatch;
found : () => Unit
required: Runnable
val r: Runnable = () => println("Run!")
Compile
Solution???
Solution
val r: Runnable = new Runnable() { def run() = println("Run!") }
Explicitly implement Runnable interface anonymously in Scala
Solution
val r: Runnable = new Runnable() { def run() = println("Run!") }
Explicitly implement Runnable interface anonymously in Scala
What’s the problem with this approach?
Solution
val r: Runnable = new Runnable() { def run() = println("Run!") }
Explicitly implement Runnable interface anonymously in Scala
Its too verbose!
What can be other solution?
Alternative Solution
Use Scala 2.12
Alternative Solution
Use Scala 2.12
But why?
Alternative Solution
Use Scala 2.12
But why?
Because Scala 2.12 accepts a function literal as a valid expression for any Single Abstract Method (SAM) type
Example
It works!
It doesn’t work!
Key Features of Scala 2.12
● A trait compiles directly to an interface with default methods. This improves binary compatibility and Java interoperability.
● Scala and Java 8 interop is also improved for functional code, as methods that take functions can easily be called in both directions using lambda syntax. The FunctionN classes in Scala’s standard library are now Single Abstract Method (SAM) types, and all SAM types are treated uniformly – from type checking through code generation. No class file is generated for a lambda, invokedynamic is used instead.
Examples of Kafka Streams with Scala
Example #1 – Simple Pipeline
Example #2 – Mapped Pipeline (w/o SAM)
Example #2 – Mapped Pipeline (with SAM)
Example #2 – Aggregation Pipeline (w/o SAM)
Example #2 – Aggregation Pipeline (with SAM)
There are other Examples too - https://github.com/knoldus/kafka-streams-scala-examples
References
● https://kafka.apache.org/documentation/streams/● http://www.scala-lang.org/news/2.12.0/#lambda-syntax-for-sam-types
Thank You