Top 20 Spring Interview Questions and Answers
Top 20 Spring Interview Questions and Answers Work through these 20 questions out loud. Open any question for the full model answer, the trap to avoid, and the follow-up a panel usually asks.
How does Bean Validation work in Spring Boot 3?
DTO fields: @NotBlank, @Email, @Size. Controller: createUser(@Valid @RequestBody UserDto dto). Global @RestControllerAdvice maps MethodArgumentNotValidException to 400 + field...
How does Spring Boot auto-configuration work?
@SpringBootApplication enables @EnableAutoConfiguration, which loads candidate configs from starters. Each auto-config uses @ConditionalOn* to register beans only when...
Describe the Spring Bean lifecycle.
Container instantiates the bean, injects dependencies, runs BeanPostProcessors, then @PostConstruct or InitializingBean. Singleton lives for context lifetime; prototype creates...
What is the N+1 query problem and how do you fix it?
Loading 100 orders then accessing each order's items triggers 101 queries. Fix with JOIN FETCH in JPQL, @EntityGraph on repository method, or a DTO query selecting only...
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...
@RestController vs @Controller?
@Controller is for traditional MVC — return "user/list" view name. @RestController adds @ResponseBody so return types become JSON/XML body — standard for REST APIs. Use...
How does @Transactional work?
Spring creates a proxy around @Transactional beans. Calling createOrder() from another bean starts a transaction on the thread-bound EntityManager; commit on success, rollback...
Explain JWT authentication flow in Spring Security.
POST /login with credentials → auth provider validates → issue JWT with exp/sub/roles. Subsequent requests include Bearer token. JwtAuthenticationFilter runs before...
What are Spring Boot starters?
spring-boot-starter-web brings spring-webmvc, Tomcat, Jackson with tested versions and enables WebMvcAutoConfiguration. You declare one starter instead of 10 coordinates....
How do you handle exceptions globally in Spring?
Create @RestControllerAdvice with @ExceptionHandler(MethodArgumentNotValidException.class) returning 400 + field map, NotFoundException → 404, generic Exception → 500 without...
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 JPA and Hibernate?
JPA is the API contract; Hibernate is the engine under Spring Boot by default. You write @Entity per JPA spec; Hibernate handles SQL generation. Spring Data JpaRepository adds...
What is CSRF and how does Spring Security handle it?
CSRF tricks logged-in user's browser to POST to your site. Spring stores CsrfToken and validates on mutating requests. For SPA with session cookies, expose token via...
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...
How do you test Spring Boot applications?
Unit test services with Mockito — no Spring. @WebMvcTest + MockMvc for controller contract. @DataJpaTest for repository queries. @SpringBootTest + Testcontainers for critical...
How do you version REST APIs?
We use /api/v1/users for clarity. Non-breaking: add optional JSON fields. Breaking: launch v2 path, maintain v1 for 6 months with Deprecation header. Spring maps...
What changed migrating Spring Boot 2 to Spring Boot 3 (Jakarta EE)?
Upgrade to Java 17+, replace imports javax.persistence → jakarta.persistence, update Spring Security config to SecurityFilterChain lambda DSL, run OpenRewrite migration recipe,...
How does spring.config.import work for externalized configuration?
In K8s: spring.config.import=optional:configtree:/etc/secrets/,optional:configtree:/etc/config/ mounts volumes as properties. Vault:...
How do Spring Boot Actuator health probes work with Kubernetes?
Enable probes, configure K8s readinessProbe on /actuator/health/readiness, liveness on /actuator/health/liveness. Custom HealthIndicator for critical deps on readiness group...
What are GraalVM native image considerations for Spring Boot?
Use spring-boot-maven-plugin native profile + GraalVM 21. Run integration tests on native binary. Register reflection for Jackson/custom serializers. Trade longer CI builds for...
Spring Interview Questions and Answers · Top 50 Spring Interview Questions and Answers (2026 Edition) · Top 40 Spring Interview Questions | Must-Prepare before interview. · Spring Interview Questions Every Fresher Must Know
All interview question lists · Interview guides · Home · Support the platform