Spring Core Interview Questions for 2–3 Years
Spring Core Interview Questions for 2–3 Years Work through these 12 questions out loud. Open any question for the full model answer, the trap to avoid, and the follow-up a panel usually asks.
@Primary vs @Qualifier — when to use each?
Two DataSource beans: @Primary mainDataSource for JPA, @Qualifier("analytics") for reporting repo. Prefer @Qualifier when both are equally valid — @Primary for sensible...
ApplicationContext vs BeanFactory — what extra does ApplicationContext provide?
BeanFactory sufficient for minimal DI tests. ApplicationContext adds @EventListener infrastructure, @MessageSource for i18n, Environment integration. Spring Boot creates...
How does Spring Environment resolve property precedence?
Debug with --debug or Environment.getPropertySources(). K8s secret as env var overrides application-prod.yml — intentional for secrets. Document precedence for team. Use...
How do Spring application events work with @EventListener?
OrderService publishes OrderCreatedEvent after save. EmailListener @EventListener sends confirmation. @TransactionalEventListener(AFTER_COMMIT) prevents email on rolled-back...
Multiple beans of the same type exist and Spring throws an error. How do you fix it?
Spring needs disambiguation when two `@Service` implement the same interface. ```java @Primary @Service public class StripePaymentGateway implements PaymentGateway {} @Service...
What is dependency injection and why does Spring use it?
DI supplies collaborators from outside the class — typically via constructor. Problem solved: tight coupling to concrete classes, hard unit tests, scattered object...
Difference between @Component, @Service, @Repository?
All register as singleton beans via component scan. Choose by layer for readability: @Repository on DAOs (plus SQLException translation), @Service on business logic, @Component...
What is the difference between @Configuration and @Component?
AppConfig @Configuration with @Bean DataSource — calling dataSource() from another @Bean method returns same instance. Mistake: @Component Config { @Bean Service s() { return...
What does @Lazy mean on injection and on @Configuration?
ServiceA needs ServiceB and vice versa — @Lazy on one injection breaks cycle via proxy. Heavy ReportGenerator @Lazy on admin-only path. Prefer refactoring to remove cycles....
BeanFactoryPostProcessor vs BeanPostProcessor — explain both.
BFPP: replace ${placeholder} in definitions via PropertySourcesPlaceholderConfigurer. BPP: @Autowired injection, @PostConstruct detection, AOP proxy wrapping. Custom BPP can...
Describe the Spring Bean lifecycle.
Container instantiates the bean, injects dependencies, runs BeanPostProcessors, then @PostConstruct or InitializingBean. Singleton lives for context lifetime; prototype creates...
Bean scopes in Spring — singleton vs prototype?
Default singleton shares one instance — stateless services. Prototype for per-operation objects. Request/session scopes tie to web lifecycle with proxies. Prototype inside...
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