Java

121 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.

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.

Kafka Connect: Failed to Find Any Class That Implements Connector

Kafka Connect throws 'Failed to find any class that implements Connector' when plugin.path is wrong or classloader isolation hides your JAR. Here's the fix.

Kafka SerializationException: Can't Convert Value of Class Fix

Kafka SerializationException: Can't convert value of class X to StringSerializer? The ClassCastException behind it, the config fix, and the safer design.

Kafka: Cannot Perform Operation After Producer Closed

Kafka IllegalStateException 'Cannot perform operation after producer has been closed' explained: why it happens, the Spring share

Kafka: Consumer Is Not Subscribed to Any Topics — Fix

IllegalStateException: Consumer is not subscribed to any topics or assigned any partitions — why poll() throws it, the subscribe/assign contract, and the fix.

Kafka BufferExhaustedException: Fix Failed to Allocate Memory

Kafka producer throws BufferExhaustedException: failed to allocate memory within max blocking time? Here's why buffer.memory fills up and the exact fix.

Kafka "Connection to node -1 could not be established" — Fix

Fix Kafka's "Connection to node -1 (localhost/127.0.0.1:9092) could not be established. Broker may not be available" — the Docker advertised.listeners fix.

Kafka SerializationException: Fixing Poison Pill Records

Kafka SerializationException: "Error deserializing key/value" crashes your consumer in a loop. Fix it with ErrorHandlingDeserializer and a dead letter topic.