David Kumar

Apache Kafka provides distributed messaging for event-driven architectures. Spring Kafka simplifies producer and consumer implementations. KafkaTemplate sends messages to topics. @KafkaListener consumes messages asynchronously. I configure serializers

Spring's @Scheduled annotation enables method execution on fixed intervals or cron expressions. @EnableScheduling activates scheduling infrastructure. Fixed delay waits after completion, fixed rate executes at intervals regardless of duration. Cron ex

Bean Validation (JSR 380) validates objects using annotations. Common constraints include @NotNull, @NotBlank, @Size, @Email, @Min, @Max, and @Pattern. I apply annotations to fields, methods, or parameters. @Valid triggers validation in Spring control

MapStruct generates type-safe bean mappers at compile-time, eliminating manual mapping code. I define mapper interfaces with @Mapper annotation—MapStruct generates implementations. @Mapping annotations handle different property names or custom convers

Spring Cache abstraction simplifies caching with annotations. @Cacheable caches method results—subsequent calls with same arguments return cached values. @CachePut always executes methods and updates cache. @CacheEvict removes entries or clears entire

The Builder pattern creates complex objects step-by-step, improving readability and flexibility. I implement builders with static inner classes—fluent methods return the builder for chaining. Required fields use constructor parameters, optional fields

Spring Security secures applications with authentication and authorization. I configure security with SecurityFilterChain bean defining protected and public endpoints. JWT (JSON Web Tokens) provides stateless authentication—tokens contain user claims

Spring Cloud provides tools for building distributed microservices. I use Spring Cloud Netflix Eureka for service discovery—services register themselves and discover others dynamically. Ribbon enables client-side load balancing. Feign creates declarat

JUnit 5 provides a modern testing framework with @Test, @BeforeEach, @AfterEach lifecycle hooks. Mockito creates test doubles with @Mock and @InjectMocks annotations. I use when().thenReturn() to stub method responses and verify() to confirm interacti

CompletableFuture enables non-blocking asynchronous programming in Java. I use supplyAsync() to run tasks in thread pools and thenApply() to chain transformations. thenCompose() flattens nested futures, while thenCombine() merges independent futures.

Global exception handling in Spring uses @ControllerAdvice to centralize error responses across all controllers. I define @ExceptionHandler methods for specific exceptions, returning consistent error DTOs with HTTP status codes. Custom exceptions exte

Spring Data JPA eliminates boilerplate DAO code with repository interfaces. I extend JpaRepository to get CRUD methods automatically—save, findById, findAll, delete. Custom query methods use method naming conventions—findByEmailAndActiveTrue generates