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Gopi Gorantala

I'm Gopi — 15+ years in Java, building Kafka and Flink platforms for banks, where one lost event is a financial discrepancy. I write javahandbook.com because the guides I needed didn't exist. Everything here is tested against a real cluster first.

Kafka InvalidReplicationFactorException: Larger Than Available Brokers

Fix Kafka's InvalidReplicationFactorException — "Replication factor: 3 larger than available brokers: 1" — in Docker and single-broker dev setups fast.

Kafka ListenerNotFoundException: No Matching Listener Fix

Kafka ListenerNotFoundException and 'leader brokers without a matching listener' explained: why the leader lacks the listener, how to reproduce, and the fix.

Kafka: Marking the Coordinator Dead — Causes and Fix

Kafka consumer stuck logging 'Marking the coordinator dead' / 'Group coordinator is unavailable or invalid, will attempt rediscovery'. Here's the real cause and the fix.

Mastering Spring Boot: Building Production-Ready Microservices

Spring Boot has revolutionized Java application development by eliminating boilerplate configuration and providing a streamlined approach to building production-ready applications. In this comprehensive guide, we'll explore advanced Spring Boot concepts and patterns that will help you build robust, scalable microservices that can handle real-world demands. Understanding

Spring Boot Hello World Tutorial with Lombok and H2 Database – Quick Start for Beginners

Learn how to create a Hello World Spring Boot application using Lombok for cleaner code and the H2 in-memory database for rapid development. This step-by-step guide includes annotations, project setup, REST API, H2 console access, and more to kickstart your Spring Boot journey.

Spring Boot Hello World Tutorial with Lombok and H2 Database – Quick Start for Beginners

How to fix port 8080 already in use error on Windows and macOS

Getting the “Web server failed to start. Port 8080 was already in use” error? Learn how to identify and kill the process blocking port 8080 on Windows and macOS using simple terminal commands. Fix server startup issues fast and keep your development running smoothly.

How to fix port 8080 already in use error on Windows and macOS

Spring vs. Spring Boot: Key Differences Developers Must Know

Spring or Spring Boot? One gives you full control, the other gets you up and running fast. If you're building Java apps, knowing the difference isn't optional—it’s critical. Here’s the breakdown every dev should read.

Spring vs. Spring Boot: Key Differences Developers Must Know

NoSuchBeanDefinitionException: The Most Common Spring Bean Error

Learn how to fix NoSuchBeanDefinitionException in Spring Boot with clear examples and best practices for dependency injection, package scanning, and bean registration.

NoSuchBeanDefinitionException for a missing bean in the ApplicationContext.

BeanCurrentlyInCreationException: Circular Dependencies in Spring

Spring Boot’s DI can backfire with the dreaded BeanCurrentlyInCreationException, signaling an unresolvable circular dependency. Learn why cycles occur, how they breach SOLID principles, and three fixes—refactor to break loops, use @Lazy injection, and static @Bean factory methods—to restore startup.

Circular dependencies in Spring causing a BeanCurrentlyInCreationException

What are the different approaches or styles in designing and building APIs?

REST, SOAP, GraphQL, and gRPC are some approaches or styles in designing and building APIs. This lesson talks about each of them in detail with tabulation comparison.