Kafka Streams Stateful Operations

Stateful operations, also referred to as aggregations, are used to combine multiple input values into a single output value. Kafka Streams support the following stateful operators:

• reduce: This combines multiple input values of type A into a single output A.

• aggregate: This combines multiple input values of type A into a single output B.

• count: This counts the number of events by key.

Because aggregations involve combining multiple values associated with the same key, we ...