Spring Boot Quiz (Advanced) - All Questions

This advanced Spring Boot quiz targets experienced developers and senior interview preparation. It focuses on deep internals, performance tuning, transactions, security, auto-configuration, and real-world production scenarios.

Question 1: Why does self-invocation break @Transactional behavior in Spring Boot?

Transaction manager fails
Proxy is bypassed
Bean is not loaded
Database connection closes

Explanation: Self-invocation bypasses the Spring proxy, so transactions are not applied.

Question 2: Which transaction propagation always starts a new transaction?

REQUIRED
SUPPORTS
MANDATORY
REQUIRES_NEW

Explanation: REQUIRES_NEW suspends the existing transaction and starts a new one.

Question 3: Why is @Transactional ineffective on private methods?

Annotation ignored
Compilation issue
Proxy cannot intercept private methods
Bean not created

Explanation: Spring proxies cannot intercept private methods.

Question 4: Which proxy mechanism does Spring Boot use by default for transactions?

Only JDK dynamic proxies
Only CGLIB proxies
ByteBuddy proxies
JDK or CGLIB based on class

Explanation: Spring uses JDK proxies or CGLIB depending on the target class.

Question 5: What is the main risk of Open Session in View (OSIV)?

Deadlocks
N+1 query problem
Transaction rollback
Memory leaks

Explanation: OSIV can hide inefficient N+1 database queries.

Question 6: Which annotation conditionally creates a bean only if none exists?

@Conditional
@ConditionalOnClass
@ConditionalOnMissingBean
@ConditionalOnProperty

Explanation: It creates a bean only when no other bean of that type exists.

Question 7: Which Spring Boot component loads auto-configuration classes?

ApplicationContext
SpringFactoriesLoader
BeanFactory
Environment

Explanation: SpringFactoriesLoader loads auto-configurations from spring.factories.

Question 8: Why is RestTemplate discouraged in new Spring Boot applications?

Deprecated
Blocking I/O
Limited HTTP support
Security issues

Explanation: RestTemplate uses blocking I/O; WebClient is non-blocking.

Question 9: Which WebClient feature enables reactive programming?

CompletableFuture
Mono and Flux
ThreadPoolExecutor
Callable

Explanation: Mono and Flux support reactive, non-blocking streams.

Question 10: Which annotation enables method-level security before execution?

@PostAuthorize
@Secured
@PreAuthorize
@EnableSecurity

Explanation: @PreAuthorize checks authorization before method execution.

Question 11: What is the default password encoder in Spring Security 5+?

BCryptPasswordEncoder
NoOpPasswordEncoder
DelegatingPasswordEncoder
PBKDF2Encoder

Explanation: DelegatingPasswordEncoder supports multiple encoders.

Question 12: Which class manages the Spring Security filter chain?

AuthenticationManager
SecurityContextHolder
FilterChainProxy
AccessDecisionManager

Explanation: FilterChainProxy manages the security filter chain.

Question 13: Which actuator endpoint exposes thread dumps?

/metrics
/beans
/threaddump
/env

Explanation: /threaddump provides JVM thread information.

Question 14: What is the purpose of SmartLifecycle?

Lazy loading
Graceful startup and shutdown
Bean destruction
Async execution

Explanation: SmartLifecycle controls startup and shutdown order.

Question 15: Which annotation helps inject prototype beans dynamically?

@Autowired
@Lazy
@Lookup
@Inject

Explanation: @Lookup retrieves a new prototype bean at runtime.

Question 16: What happens when a prototype bean is injected into a singleton?

New instance every call
Only one instance injected
Injection fails
Scope ignored

Explanation: Prototype is resolved only once during injection.

Question 17: Which Spring component customizes beans before initialization?

BeanFactory
BeanPostProcessor
ApplicationContext
BeanDefinitionReader

Explanation: BeanPostProcessor modifies beans before and after initialization.

Question 18: Which order is followed for BeanPostProcessors?

Registration order
Random order
PriorityOrdered → Ordered → Others
Alphabetical order

Explanation: Spring follows PriorityOrdered, then Ordered, then others.

Question 19: Which annotation prevents transaction rollback for specific exceptions?

rollbackFor
noRollbackFor
@NoRollback
@IgnoreRollback

Explanation: noRollbackFor excludes exceptions from rollback.

Question 20: Which isolation level prevents dirty reads?

READ_UNCOMMITTED
READ_COMMITTED
REPEATABLE_READ
SERIALIZABLE

Explanation: READ_COMMITTED prevents reading uncommitted data.

Question 21: Which executor is used by default for @Async?

ThreadPoolTaskExecutor
ForkJoinPool
SimpleAsyncTaskExecutor
CachedThreadPool

Explanation: SimpleAsyncTaskExecutor is the default async executor.

Question 22: What is a major drawback of SimpleAsyncTaskExecutor?

Low throughput
No thread reuse
Blocking behavior
Memory leaks

Explanation: It creates a new thread per task without reuse.

Question 23: Which annotation enables scheduling support?

@EnableAsync
@EnableScheduling
@Scheduled
@EnableTasks

Explanation: @EnableScheduling enables scheduled task execution.

Question 24: Which annotation dynamically imports configuration classes?

@Import
@ComponentScan
@EnableAutoConfiguration
@Configuration

Explanation: @Import loads additional configuration classes.

Question 25: What is the role of @ImportSelector?

Import properties
Conditionally select configurations
Enable profiles
Scan components

Explanation: @ImportSelector selects configurations dynamically.

Question 26: Which Spring Boot feature supports graceful shutdown?

Actuator
Lifecycle
SmartLifecycle
ShutdownHook

Explanation: SmartLifecycle enables graceful shutdown.

Question 27: Which annotation enables JPA auditing?

@EnableAuditing
@EnableJpaAuditing
@Audit
@JpaAudit

Explanation: It enables created/modified auditing fields.

Question 28: Which issue occurs if multiple @Primary beans exist?

Compilation error
Random injection
Startup failure
Beans ignored

Explanation: Multiple primary beans cause startup failure.

Question 29: Which component resolves @Value placeholders?

Environment
PropertySource
PropertyPlaceholderConfigurer
ResourceLoader

Explanation: PropertyPlaceholderConfigurer resolves placeholders.

Question 30: Why is caching often placed at service layer?

Better UI
Reduced DB load
Simpler controllers
Faster serialization

Explanation: Service-layer caching reduces database calls.

Question 31: Which annotation evicts cache entries?

@CachePut
@CacheClear
@CacheRemove
@CacheEvict

Explanation: @CacheEvict removes cached data.

Question 32: What is the default cache key for @Cacheable?

Method name
Random UUID
All method parameters
Return value

Explanation: Method parameters are used as cache key.

Question 33: Which failure occurs if @EnableAspectJAutoProxy is missing?

Application crash
Beans not created
AOP not applied
Transactions ignored

Explanation: Without it, AOP proxies are not created.

Question 34: Which Spring Boot feature exposes health and metrics?

Spring Security
Spring AOP
Spring Actuator
Spring Context

Explanation: Spring Actuator provides monitoring endpoints.

Question 35: Which actuator endpoint exposes environment properties?

/info
/metrics
/env
/health

Explanation: /env exposes environment configuration.

Question 36: Which issue is caused by blocking calls in WebFlux?

Deadlocks
Thread starvation
Event loop blocking
Memory leaks

Explanation: Blocking calls block the reactive event loop.

Question 37: Why is stateless authentication preferred in Spring Boot microservices?

Less code
Horizontal scalability
Lower latency
Better caching

Explanation: Stateless services scale more easily.

Question 38: Which deployment strategy enables zero downtime?

Rolling restart
Blue-green deployment
Manual deployment
Single instance

Explanation: Blue-green deployment avoids downtime.

Question 39: Which issue can occur if async exceptions are not handled?

Compilation error
Silent failures
Thread deadlock
DB corruption

Explanation: Async exceptions can fail silently.

Question 40: Which logging practice is recommended in production?

console.log
Structured logging
Client-side logging
No logging

Explanation: Structured logs improve observability.

Question 41: Why is API versioning important in Spring Boot?

SEO
Backward compatibility
Smaller payloads
Caching

Explanation: Versioning avoids breaking existing clients.

Question 42: Which annotation disables a specific auto-configuration?

@DisableAutoConfig
@ExcludeAutoConfiguration
@SpringBootApplication(exclude)
@IgnoreAutoConfig

Explanation: Exclude attribute disables auto-config classes.

Question 43: Which Spring Boot risk arises from exposing all actuator endpoints?

Performance drop
Security exposure
Memory leaks
Thread blocking

Explanation: Sensitive data can be exposed publicly.

Question 44: Which component publishes Spring application events?

EventPublisher
ApplicationContext
BeanFactory
DispatcherServlet

Explanation: ApplicationContext publishes application events.

Question 45: Which annotation listens to Spring application events?

@OnEvent
@EventHandler
@EventListener
@Listener

Explanation: @EventListener handles application events.

Question 46: Which Spring Boot practice improves fault tolerance?

Single instance
Circuit breaker patterns
Synchronous APIs
Large payloads

Explanation: Circuit breakers prevent cascading failures.

Question 47: Why should configuration be externalized in Spring Boot?

Smaller JAR size
Environment flexibility
Faster startup
Better logging

Explanation: Externalized config supports multiple environments.

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