Cracking the JPA Interview: Tips and Must-Know Questions

Cracking the JPA Interview: Tips and Must-Know Questions 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 JPA Specifications (Criteria API) help dynamic queries?

   UserSearchSpec.withStatus(status).and(withNameLike(name)) — repository.findAll(spec, pageable). Criteria API verbose — wrap in static factory methods. Alternative: Querydsl or...

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2. 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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3. 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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4. 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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5. 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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6. 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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7. When use @Query native SQL vs JPQL in Spring Data JPA?

   JPQL for standard entity fetches and portable logic. Native for PostgreSQL-specific jsonb queries, recursive CTEs, or performance-tuned index hints after EXPLAIN. Interface...

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8. How do Flyway/Liquibase integrate with Spring Boot JPA?

   Prod: spring.jpa.hibernate.ddl-auto=validate, Flyway V1__init.sql through Vn. CI: @Testcontainers PostgreSQL + Flyway migrate + integration tests. Never rename column without...

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9. 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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10. 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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11. What is JPA auditing with @CreatedDate and @LastModifiedDate?

    @EnableJpaAuditing + AuditorAware<String> from SecurityContextHolder. Entity: @CreatedDate Instant createdAt; @LastModifiedDate Instant updatedAt. Works with auditing on save()...

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12. 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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