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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