Spring Framework Case Studies & Practical Application 4 — Questions and Answers
Question 1: A Spring Boot application experiences 'BeanCurrentlyInCreationException' at startup. What is the most common root cause?
- Missing @Autowired annotation on a required dependency
- A circular dependency where Bean A depends on Bean B and Bean B depends on Bean A (Correct answer)
- Two beans with the same name defined in different @Configuration classes
- A @Lazy bean being injected into an eager singleton
Correct answer: A circular dependency where Bean A depends on Bean B and Bean B depends on Bean A
Circular dependencies occur when two or more beans depend on each other, preventing the IoC container from instantiating either without the other already existing.
Question 2: You need to write an integration test for a Spring MVC controller without starting a full server. Which testing slice annotation should you use?
- @SpringBootTest(webEnvironment=RANDOM_PORT)
- @WebMvcTest(YourController.class) (Correct answer)
- @DataJpaTest
- @ContextConfiguration with an embedded server
Correct answer: @WebMvcTest(YourController.class)
@WebMvcTest loads only the web layer (controllers, filters, advice) and provides MockMvc, making it fast without starting a full embedded server.
Question 3: A scheduled Spring Batch job fails halfway through. On the next run, it should skip already-processed records. Which Batch feature supports this?
- Restarting the JVM with a different input file each run
- Spring Batch's JobRepository with restartable jobs — it tracks step execution state and resumes from the last checkpoint (Correct answer)
- Using @Transactional(propagation=NESTED) around each chunk
- Filtering processed records in application code by querying an audit table
Correct answer: Spring Batch's JobRepository with restartable jobs — it tracks step execution state and resumes from the last checkpoint
Spring Batch stores job and step execution metadata in its JobRepository, allowing a failed job to restart exactly where it left off at the chunk boundary.
Question 4: A Spring WebFlux endpoint must call two independent services in parallel and combine results. Which reactive operator achieves this?
- Mono.zip(serviceAMono, serviceBMono) (Correct answer)
- serviceAMono.flatMap(a -> serviceBMono)
- Flux.concat(serviceAMono, serviceBMono)
- serviceAMono.block() followed by serviceBMono.block()
Correct answer: Mono.zip(serviceAMono, serviceBMono)
Mono.zip subscribes to both Monos simultaneously and emits a tuple when both complete, achieving true parallel execution without blocking.
Question 5: A Spring Boot application must use different database credentials in dev, staging, and production environments. What is the recommended approach?
- Hard-code credentials in application.properties and override with system environment variables in higher environments
- Use Spring Profiles with separate application-{profile}.properties files and inject credentials via environment variables or Vault (Correct answer)
- Store credentials in a Git-tracked application-prod.properties file
- Use a single application.properties with placeholders filled at build time by Maven
Correct answer: Use Spring Profiles with separate application-{profile}.properties files and inject credentials via environment variables or Vault
Spring Profiles combined with externalized secrets (environment variables or HashiCorp Vault) keep credentials out of source control and environment-specific.
Question 6: After enabling Spring Cache with @EnableCaching and @Cacheable, a service method still executes on every call. What is a common misconfiguration cause?
- @Cacheable is not supported on @Service beans
- The method is called internally within the same class, bypassing the Spring proxy (Correct answer)
- The cache manager bean name must be exactly 'cacheManager' or it is ignored
- The @EnableCaching annotation must be on the @Service class, not @Configuration
Correct answer: The method is called internally within the same class, bypassing the Spring proxy
Spring AOP caching works via proxy; calling a @Cacheable method from within the same class skips the proxy and therefore skips the cache.
Question 7: A team needs to enforce a rule that every new Spring bean in the 'com.example.service' package is tested with an integration test. Which approach best enforces this architectural rule?
- Code review checklists that remind developers to write tests
- ArchUnit tests that assert every class in the service package has a corresponding test class (Correct answer)
- A custom Spring BeanPostProcessor that logs untested beans at startup
- A Checkstyle rule that requires a @Test annotation on every class
Correct answer: ArchUnit tests that assert every class in the service package has a corresponding test class
ArchUnit allows expressing and automatically enforcing architectural rules (such as test coverage requirements by package) as JUnit tests that fail the build if violated.
Spring Framework Case Studies & Practical Application 4
A Spring Boot application experiences 'BeanCurrentlyInCreationException' at startup.
What is the most common root cause?