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Posted to jira@kafka.apache.org by "A. Sophie Blee-Goldman (Jira)" <ji...@apache.org> on 2021/09/30 01:44:00 UTC
[jira] [Created] (KAFKA-13336) Migrate StreamsBuilder class to
interface with factory method on KafkaStreams
A. Sophie Blee-Goldman created KAFKA-13336:
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Summary: Migrate StreamsBuilder class to interface with factory method on KafkaStreams
Key: KAFKA-13336
URL: https://issues.apache.org/jira/browse/KAFKA-13336
Project: Kafka
Issue Type: Improvement
Components: streams
Reporter: A. Sophie Blee-Goldman
In order to refactor and improve the streams physical plan generation, we'll need to clean up the DSL builder API a bit and in particular enforce the configs be passed in from the beginning, rather than only when calling #build. We can also use this opportunity to improve the disconnect between the builder, the resulting Topology, and the Kafka Streams application that ultimately runs this topology – at the moment these are all completely uncoupled on the surface, so it's easy to think that a StreamsBuilder can be reused to build multiple Topology objects, or that a Topology object could be passed in to different KafkaStreams. However there is internal state that is shared and modified during StreamsBuilder#build and in the KafkaStreams constructor, and they are actually very coupled under the hood meaning there must be a 1:1:1 ratio of builder to topology to KafkaStreams. So we need a new API that
# Forces users to pass in the configs (Properties) when constructing the builder
# Clarifies the relationship of the builder object to the topology, and to the app itself
I think a good API for this might look something like this:
# Move the StreamsBuilder class to an internal one (technically we would need to keep it where it is for now until a full deprecation cycle)
# Introduce a TopologyBuilder interface to replace the functionality of the current StreamsBuilder class, and have StreamsBuilder implement this. All the current methods on StreamsBuilder will be moved to the TopologyBuilder interfaces
# Add a factory method on KafkaStreams for users to get instances of the TopologyBuilder, and have this accept a Properties. For example
{code:java}
class KafkaStreams {
public void newTopologyBuilder(final Properties props) {
// convert to StreamsConfig to validate configs & check for application.id
final StreamsConfig config = new StreamsConfig(props);
return new StreamsBuilder(config);
}
}{code}
This should satisfy both of the requirements, and imo provides a cleaner API anyways. Getting the builder through a factory method on the KafkaStreams object should make it clear that this builder is tied to that particular KafkaStreams instance. And we can enforce that it isn't reused for a different application by parsing the Properties passed in to KafkaStreams#newTopologyBuilder, specifically the application.id
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