ContextQMD
Back to Kafka

Migrating from Streams Scala to Java API

docs/streams/developer-guide/scala-migration.md

4.2.03.4 KB
Original Source
<!-- Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. -->

⚠️ DEPRECATION NOTICE: The kafka-streams-scala library is deprecated as of Kafka 4.3 and will be removed in Kafka 5.0. This guide will help you migrate your Scala applications to use the Java Streams API directly. For more information, see KIP-1244.

Migration Overview

The Java Streams API works well from Scala with minimal adjustments. The main differences are:

  1. Use Java types directly instead of Scala wrapper classes
  2. Configure Serdes explicitly via StreamsConfig or pass them to methods

Example: Word Count Application

Scala Wrapper Approach (Deprecated)

scala
import java.util.Properties

import org.apache.kafka.streams.scala.ImplicitConversions._
import org.apache.kafka.streams.scala._
import org.apache.kafka.streams.scala.kstream._
import org.apache.kafka.streams.{KafkaStreams, StreamsConfig}
import org.apache.kafka.streams.scala.serialization.Serdes._

object WordCountScala extends App {
  val props = new Properties()
  props.put(StreamsConfig.APPLICATION_ID_CONFIG, "wordcount")
  props.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092")

  val builder = new StreamsBuilder  // Scala wrapper
  val textLines: KStream[String, String] = builder.stream[String, String]("input-topic")

  val wordCounts: KTable[String, Long] = textLines
    .flatMapValues(line => line.toLowerCase.split("\\W+"))
    .groupBy((_, word) => word)
    .count()

  wordCounts.toStream.to("output-topic")

  val streams = new KafkaStreams(builder.build(), props)
  streams.start()
}

Java API Approach

scala
import java.util.Properties

import org.apache.kafka.streams.{KafkaStreams, StreamsBuilder, StreamsConfig}
import org.apache.kafka.streams.kstream.{KStream, KTable, Produced}
import org.apache.kafka.common.serialization.Serdes
import scala.jdk.CollectionConverters._

object WordCountJava extends App {
  val props = new Properties()
  props.put(StreamsConfig.APPLICATION_ID_CONFIG, "wordcount")
  props.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092")
  // Configure default serdes
  props.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, classOf[Serdes.StringSerde])
  props.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, classOf[Serdes.StringSerde])

  val builder = new StreamsBuilder  // Java StreamsBuilder
  val textLines = builder.stream[String, String]("input-topic")

  val wordCounts = textLines
    .flatMapValues(_.toLowerCase.split("\\W+"))
    .groupBy((_, word) => word)
    .count()

  wordCounts.toStream.to("output-topic", Produced.`with`(Serdes.String(), Serdes.Long()))

  val streams = new KafkaStreams(builder.build(), props)
  streams.start()
}