Migrating from Streams Scala to Java API
⚠️ DEPRECATION NOTICE: The
kafka-streams-scalalibrary 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:
- Use Java types directly instead of Scala wrapper classes
- Configure Serdes explicitly via
StreamsConfigor pass them to methods
Example: Word Count Application
Scala Wrapper Approach (Deprecated)
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
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()
}