Spring Framework Interview Questions

Spring is a lightweight Java framework that provides infrastructure support for developing enterprise applications.

Spring provides dependency injection, loose coupling, modular architecture, transaction management, security integration, and easier testing.

IoC is a principle where the framework manages object creation and dependency management instead of application code.

Dependency Injection is the process of supplying dependencies to objects through constructors, setters, or fields.

The main types are Constructor Injection, Setter Injection, and Field Injection.

A Spring Bean is an object that is instantiated, configured, and managed by the Spring IoC container.

The Bean Lifecycle includes instantiation, dependency injection, initialization, usage, and destruction.

Spring Boot is an extension of Spring that simplifies application setup through auto-configuration and starter dependencies.

Spring requires more manual configuration, while Spring Boot provides auto-configuration and embedded servers for rapid development.

@Autowired automatically injects dependencies managed by the Spring container.

@Component marks a class as a Spring-managed bean for component scanning.

@Service is a specialization of @Component used for service-layer classes.

@Repository is used for persistence-layer classes and enables exception translation.

@RestController combines @Controller and @ResponseBody to create RESTful web services.

Spring Boot Starters are dependency descriptors that simplify project configuration by bundling commonly used libraries.

Name concrete APIs (collections, concurrency, streams, annotations) tied to Spring Framework. Interviewers want syntax-level clarity plus when you would reach for each feature in production.

Prefer specific checked/unchecked exceptions, wrap lower-level failures with context, and avoid empty catch blocks. For Spring Framework, decide what is recoverable vs fatal to the request thread.

JUnit 5 with Arrange-Act-Assert, Mockito for collaborators, and parameterized tests for edge cases. Keep Spring Framework logic pure where possible so tests stay fast.

Incorrect equals/hashCode break HashMap/HashSet behavior. If Spring Framework stores objects in collections, explain the contract and mutability pitfalls.

Retain only needed references, prefer streaming for large datasets, and avoid accidental caches. Relate leaks or GC pressure to a concrete Spring Framework scenario.