Java

130 Posts

Java is both a programming language and a platform — and today it's sleeker, faster, and more powerful than ever. Statically-typed and JVM-based, its legendary write-once-run-anywhere portability remains a core strength, backed by a vast ecosystem (Spring, Kafka, Flink) for production-grade systems. Strong compile-time safety meets mature tooling for concurrency and distributed processing, making Java the backbone of large-scale, real-time, enterprise-critical apps in banking and cloud.

Kafka NotLeaderOrFollowerException: Cause and Fix

Producer or consumer failing with NotLeaderOrFollowerException (NOT_LEADER_OR_FOLLOWER)? Why stale leader metadata causes it and how to fix it for good.

Kafka InconsistentGroupProtocolException: Cause and Fix

Kafka InconsistentGroupProtocolException: the group member's supported protocols are incompatible. Why it hits mid-upgrade and how to fix the assignor mismatch.

Kafka InvalidTxnStateException: Causes and How to Fix It

InvalidTxnStateException means your producer called a transactional API in the wrong state. Here's the state machine, the exact triggers, and the fix.

Kafka: Assignments Can Only Be Reset If the Group Is Inactive

Kafka's reset-offsets fails with 'Assignments can only be reset if the group is inactive, but the current state is Stable.' Here's why, and the fix.

Kafka InvalidTopicException: Why It Happens and How to Fix It

Kafka InvalidTopicException — 'Topic name is illegal' from bad characters, 249-char limits, or '.'/'_' collisions. The exact rules, root cause, and the fix.

Kafka NotEnoughReplicasException: Fix NOT_ENOUGH_REPLICAS Errors

Kafka NotEnoughReplicasException: messages rejected since there are fewer in-sync replicas than required. Fix min.insync.replicas vs acks=all, fast.

Kafka RebalanceInProgressException: Why It Happens and How to Fix It

Kafka RebalanceInProgressException on commitSync/commitAsync with CooperativeStickyAssignor? Here's why it's not CommitFailedException, and the correct fix.

Fix KafkaConsumer Is Not Safe for Multi-Threaded Access

Hitting ConcurrentModificationException: KafkaConsumer is not safe for multi-threaded access? Here's why the thread guard fires and the correct fix.

Kafka IllegalStateException: No Current Assignment for Partition

Getting java.lang.IllegalStateException: No current assignment for partition on seek()? Why Kafka's lazy assignment causes it — and the correct fix.

Kafka Connect Failed to Flush: Offset Commit Timeout Fix

Kafka Connect source task logs 'Failed to flush, timed out while waiting for producer to flush outstanding N messages'. Here's the real cause and the fix.