Top 20 Spring Transactions Interview Questions and Answers
Top 20 Spring Transactions 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.
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 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...
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...
Saga pattern — choreography vs orchestration?
Order saga: reserve inventory → charge payment → ship. Failure at payment triggers release inventory compensation. Orchestration clearer for complex flows with visibility....
Explain the transactional outbox pattern.
OrderService @Transactional saves Order and OutboxEvent(type=ORDER_CREATED, payload=json). OutboxProcessor @Scheduled polls FOR UPDATE SKIP LOCKED, sends to Kafka, updates...
Load shedding and backpressure in microservices?
Tomcat max queue + reject policy returns 503 with Retry-After. WebClient timeout + circuit breaker stops calling slow dependency. Kafka consumer pause partitions when...
What happens if @Transactional fails midway? How do you verify rollback?
Default: runtime exception marks rollback-only; transaction commits nothing on exit. ```java @Transactional(rollbackFor = Exception.class) public void placeOrder(Order o) {...
New deployment causes random 5xx errors. Rollback fixes it. Why?
Compare metrics before/after: error rate, pool saturation, GC. Enable DEBUG temporarily in canary pod only. Check new dependency version, connection pool default change, or...
How do you stop a LangChain4j agent loop from running forever, and who owns the workflow?
I set maxSequentialToolsInvocations to a small number — three or four for triage. Writes take an idempotency key. Approve is not a @Tool. Automating a business process with AI...
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...
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...
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