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Hectal
Phase 7Intermediate8 of 18 in Apache Kafka

Spring Boot & Java Clients

Production-grade Spring Kafka producers and consumers: JSON events with keys and headers, idempotence and compression, manual acks, error handlers, DLTs, graceful shutdown, multi-group pipelines, metrics, and testing with Testcontainers.

This phase turns the concepts into code you'd ship: the syllabus's coding problems implemented with Spring Boot 3 and Spring for Apache Kafka, with every setting explained.

The same ideas apply to other clients (librdkafka-based clients in Go, Python and .NET, or KafkaJS); notes appear where their behaviour differs.

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4 topics ~30 min 8 code blocks & diagrams
Start with the first topic
1
7.1

A Production Spring Boot Producer

Configure a KafkaTemplate for JSON events with a key per entity, headers for tracing and event type, acks=all, idempotence, zstd compression and batching, and handle send results asynchronously so failures are logged, counted and never silently dropped.

7 min 2 code practice

2
7.2

A Production Spring Boot Consumer

A robust listener uses manual acknowledgement after processing, an ErrorHandlingDeserializer, a DefaultErrorHandler with backoff and a DeadLetterPublishingRecoverer, cooperative rebalancing, sensible concurrency, and graceful shutdown so in-flight records finish and offsets are committed.

8 min 3 code practice

3
7.3

The Order Pipeline: Multiple Groups, Idempotency, Metrics

One orders topic feeds payment, inventory, analytics and notification services, each in its own consumer group with its own offsets, retries and DLT. Build it with idempotent handlers, structured logging of topic/partition/offset/key, and metrics for throughput, errors, lag and processing time.

8 min 1 diagram 1 code practice

4
7.4

Testing Kafka Applications

Unit-test processing logic without Kafka, test Kafka Streams topologies with TopologyTestDriver, and run integration tests against a real broker with Testcontainers (preferred) or Spring's @EmbeddedKafka. Test the failure paths: retries, DLT, duplicates and rebalances.

7 min 1 code practice