What is Kafka Streams, how does it differ from the usual Kafka operation scheme?

Kafka Streams is a library for processing data streams on top of Apache Kafka. It allows creating applications that read, process, and write data to Kafka in real-time.

Differences from the usual Kafka operation:

• High-level abstraction: Kafka Streams provides a convenient API for transforming streams, aggregations, joins, and windowed computations, whereas regular Kafka work is just reading and writing messages.
• No separate cluster: Kafka Streams runs as part of your application and does not require a separate processing cluster (unlike Kafka Connect or Apache Flink).
• State and fault-tolerance: built-in support for state stores and recovery after failures.

Example of using Kafka Streams in Java:

StreamsBuilder builder = new StreamsBuilder();
KStream<String, String> source = builder.stream("input-topic");

KStream<String, String> filtered = source.filter((key, value) -> value.contains("important"));
filtered.to("output-topic");

KafkaStreams streams = new KafkaStreams(builder.build(), props);
streams.start();

Thus, Kafka Streams simplifies the creation of stream applications with rich data processing logic, leveraging Kafka's capabilities.