Hibernate Interview Questions for 5 Years Experience

Hibernate Interview Questions for 5 Years Experience 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.

1. 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...

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2. 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,...

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3. Lazy vs eager fetching in JPA — trade-offs?

   Default associations LAZY. Service method needing orders+items uses JOIN FETCH in repository query. Disable spring.jpa.open-in-view=false — forces explicit fetch in service...

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4. 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....

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5. 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...

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6. IdentityHashMap vs HashMap — when would you use IdentityHashMap?

   Use when identity matters not value — tracking object visitation in deep graph walk. Business keys (userId, email) belong in HashMap with proper equals/hashCode....

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7. When should you use spring.main.lazy-initialization?

   Use in test slices or large batch apps where most beans unused per run. Production APIs: fix slow @PostConstruct and DB migrations instead. Combine with...

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8. 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....

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9. 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...

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10. 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...

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11. How do you handle exceptions globally in Spring?

    Create @RestControllerAdvice with @ExceptionHandler(MethodArgumentNotValidException.class) returning 400 + field map, NotFoundException → 404, generic Exception → 500 without...

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12. 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...

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