John Roesler created KAFKA-7435:
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Summary: Consider standardizing the config object pattern on
interface/implementation.
Key: KAFKA-7435
URL: https://issues.apache.org/jira/browse/KAFKA-7435
Project: Kafka
Issue Type: Improvement
Components: streams
Reporter: John Roesler
Fix For: 3.0.0
Currently, the majority of Streams's config objects are structured as a
"external" builder class (with protected state) and an "internal" subclass
exposing getters to the state. This is serviceable, but there is an alternative
we can consider: to use an interface for the external API and the
implementation class for the internal one.
Advantages:
* we could use private state, which improves maintainability
* the setters and getters would all be defined in the same class, improving
readability
* users browsing the public API would be able to look at an interface that
contains less extraneous internal details than the current class
* there is more flexibility in implementation
Alternatives
* instead of external-class/internal-subclass, we could use an external
*final* class with package-protected state and an internal accessor class (not
a subclass, obviously). This would make it impossible for users to try and
create custom subclasses of our config objects, which is generally not allowed
already, but is currently a runtime class cast exception.
Example implementation: [https://github.com/apache/kafka/pull/5677]
This change would break binary, but not source, compatibility, so the earliest
we could consider it is 3.0.
To be clear, I'm *not* saying this *should* be done, just calling for a
discussion. Otherwise, I'd make a KIP.
Thoughts?
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