Most Asked Hibernate Interview Questions in 2026

Most Asked Hibernate Interview Questions in 2026 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. 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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2. 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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3. 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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4. 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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5. 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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6. 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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7. 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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8. 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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9. 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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10. 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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11. 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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12. 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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