How to implement ConsumerRebalanceListener using Scala?
public class SaveOffsetsOnRebalance implements ConsumerRebalanceListener {
}
And what would be example of that newly made Scala rebalance listener when subscribing to topics?
Trying to learn and wrap my mind around implementing Java methods/interfaces in Scala..
Thanks.
You can just extend the interface directly
class MyListener extends ConsumerRebalanceListener {
...
}
And the example from API docs would look like:
class SaveOffsetsOnRebalance(consumer: Consumer[_, _] ) extends ConsumerRebalanceListener {
def onPartitionsRevoked(partitions: Collection[TopicPartition]): Unit = {
// save the offsets in an external store using some custom code not described
partitions.toScala.forEach(
saveOffsetInExternalStore(consumer.position(partition))
)
}
def onPartitionsAssigned(partitions: Collection[TopicPartition]): Unit = {
// read the offsets from an external store using some custom code not described here
partitions.forEach(
consumer.seek(partition, readOffsetFromExternalStore(partition)))
}
}
Just add proper imports
(consumer Consumer[_, _] ) taking as parameters?Consumer? Is a Consumer a class? This part looks like a map [_, _]. I am just not familiar with this notation (does _ means any?) and where to look for Consumer to see the that type? Thanks..
There are traits in Scala corresponding to interfaces in Java. Scala trait gets converted to Java Interfaces internally. And just like we implement interfaces in Java, the same way we extend traits in Scala. So you just need to extend that Java interfaces as if it were a Scala trait because under the hood both are same.
class SaveOffsetsOnRebalance extends ConsumerRebalanceListener {}
