Spring Interview Questions and Answers

1. What is Spring Framework?

   • Answer: Spring is an open-source application framework for Java platforms. It's designed to simplify Java EE development and provides comprehensive infrastructure support for developing robust applications. It addresses many common problems encountered in enterprise applications, such as dependency injection and aspect-oriented programming.

2. What are the core modules of Spring Framework?

   • Answer: Core Container, Data Access/Integration, AOP (Aspect-Oriented Programming), Context, Web, MVC (Model-View-Controller).

3. Explain Dependency Injection (DI).

   • Answer: DI is a design pattern where dependencies are provided to a class rather than the class creating them itself. This promotes loose coupling and testability. Spring uses DI extensively.

4. What is Inversion of Control (IoC)?

   • Answer: IoC is a design principle where the control of object creation and lifecycle is inverted. Instead of a class creating its own dependencies, a container (like the Spring container) is responsible. DI is a form of IoC.

5. Explain different types of Dependency Injection.

   • Answer: Constructor Injection (dependencies are provided through the constructor), Setter Injection (dependencies are provided through setter methods), Interface Injection (dependencies are provided through an interface).

6. What is Spring Bean?

   • Answer: A Spring Bean is an object that is instantiated, assembled, and managed by the Spring IoC container. It's defined in the Spring configuration.

7. What is the role of the Spring BeanFactory?

   • Answer: The BeanFactory is the core interface of the Spring IoC container. It's responsible for instantiating, configuring, and managing beans.

8. What is ApplicationContext?

   • Answer: ApplicationContext is an advanced interface that extends BeanFactory. It provides additional functionalities like message resource handling, event handling, and more.

9. Explain different ways to configure Spring Beans.

   • Answer: XML-based configuration, Annotation-based configuration, Java-based configuration.

10. What are Spring annotations? Give examples.

    • Answer: Annotations provide a metadata-driven way to configure Spring beans. Examples include @Component, @Service, @Repository, @Controller, @Autowired, @Qualifier, @Scope, @Configuration.

11. What is @Autowired annotation?

    • Answer: @Autowired annotation is used for automatic dependency injection. Spring automatically resolves and injects the required dependencies.

12. What is @Qualifier annotation?

    • Answer: @Qualifier annotation is used to resolve ambiguities when multiple beans of the same type are available for injection.

13. What is @Scope annotation? Explain its different values.

    • Answer: @Scope defines the scope of a bean. Values include singleton (default), prototype, request, session, application.

14. What is Spring AOP?

    • Answer: Spring AOP provides aspect-oriented programming capabilities. It allows you to add cross-cutting concerns (like logging, security, transactions) to your application without modifying the core business logic.

15. Explain different AOP concepts like Advice, Pointcut, Joinpoint, Aspect.

    • Answer: Joinpoint: A point in the execution of a program (method call, exception handling, etc.). Pointcut: A predicate that matches joinpoints. Advice: Action taken at a joinpoint (before, after, around). Aspect: A modularization of cross-cutting concerns.

16. What are different types of Advice in Spring AOP?

    • Answer: Before advice, After advice, After returning advice, After throwing advice, Around advice.

17. What is Spring Data Access/Integration?

    • Answer: Spring provides simplified support for database interaction through JDBC, ORM frameworks like Hibernate, JPA, and others.

18. Explain Spring JDBC.

    • Answer: Spring JDBC simplifies JDBC programming by providing exception handling, resource management, and simplified database interaction using JdbcTemplate.

19. What is Spring ORM?

    • Answer: Spring ORM provides integration with various Object-Relational Mapping (ORM) frameworks, abstracting away the specific ORM implementation details.

20. What is Spring MVC?

    • Answer: Spring MVC is a powerful and flexible web framework built on top of the Spring framework. It simplifies building web applications using the Model-View-Controller (MVC) design pattern.

21. Explain the components of Spring MVC.

    • Answer: DispatcherServlet, Controllers, Models, Views, ViewResolvers.

22. What is DispatcherServlet in Spring MVC?

    • Answer: DispatcherServlet is the front controller in Spring MVC. It intercepts all incoming requests and routes them to the appropriate controllers.

23. What is a Spring Controller?

    • Answer: A Spring Controller is a component that handles incoming requests, processes them, and returns a model and view to the DispatcherServlet.

24. What are different types of Spring Controllers?

    • Answer: @Controller, @RestController (combines @Controller and @ResponseBody).

25. What is Model in Spring MVC?

    • Answer: The Model represents the data that is passed between the controller and the view.

26. What is View in Spring MVC?

    • Answer: The View is responsible for rendering the data (model) to the user. It can be JSP, Thymeleaf, FreeMarker, etc.

27. What is ViewResolver in Spring MVC?

    • Answer: A ViewResolver is responsible for resolving logical view names to actual view objects (e.g., JSP files).

28. What is Spring Boot?

    • Answer: Spring Boot simplifies Spring application development by providing a convention-over-configuration approach. It reduces boilerplate code and makes it easy to create standalone, production-grade applications.

29. What are Spring Boot Starters?

    • Answer: Spring Boot starters are pre-configured dependencies that simplify the inclusion of specific functionalities in your application.

30. What is @SpringBootApplication annotation?

    • Answer: @SpringBootApplication is a convenience annotation that combines @Configuration, @EnableAutoConfiguration, and @ComponentScan.

31. Explain Spring Boot Auto-Configuration.

    • Answer: Spring Boot automatically configures your application based on the dependencies you include. It intelligently determines what beans and configurations are needed.

32. How to create a RESTful web service using Spring MVC?

    • Answer: Use the @RestController annotation and define methods that handle HTTP requests (GET, POST, PUT, DELETE) and return data directly in JSON or XML format.

33. What is Spring Security?

    • Answer: Spring Security is a framework for securing Spring-based applications. It provides authentication and authorization functionalities.

34. Explain different authentication mechanisms in Spring Security.

    • Answer: Basic authentication, Form-based authentication, LDAP authentication, OAuth 2.0, JWT (JSON Web Tokens).

35. What is Spring Data JPA?

    • Answer: Spring Data JPA simplifies JPA (Java Persistence API) development by providing a simpler interface for database operations.

36. What is @Transactional annotation?

    • Answer: @Transactional annotation is used to mark a method or class as transactional. It ensures that database operations are atomic and consistent.

37. Explain different transaction propagation behaviors.

    • Answer: REQUIRED, REQUIRES_NEW, SUPPORTS, NOT_SUPPORTED, MANDATORY, NEVER.

38. What is the difference between @Component, @Service, @Repository, and @Controller annotations?

    • Answer: They are stereotype annotations that provide semantic meaning to the beans. @Component is a general-purpose stereotype, while @Service, @Repository, and @Controller are more specific to the layer they represent in the application (service layer, data access layer, and controller layer, respectively).

39. What are the different ways to handle exceptions in Spring?

    • Answer: Using @ControllerAdvice, @ExceptionHandler, Exception translation in Spring Data JPA.

40. What is Spring Batch?

    • Answer: Spring Batch is a framework for processing large volumes of records efficiently and reliably. It's often used for batch processing tasks.

41. What is Spring Integration?

    • Answer: Spring Integration provides a framework for building enterprise integration solutions. It helps connect different systems and applications.

42. Explain the concept of Inversion of Control (IoC) container in Spring.

    • Answer: The IoC container is the heart of Spring. It manages the creation, configuration, and lifecycle of beans. It takes control of object creation from the application code.

43. How does Spring manage bean lifecycles?

    • Answer: Spring manages bean lifecycles through lifecycle callbacks (init-method and destroy-method) or using interfaces like InitializingBean and DisposableBean.

44. What is BeanPostProcessor?

    • Answer: A BeanPostProcessor is an interface that allows you to intercept the creation of beans. You can modify beans before or after initialization.

45. What is a prototype bean in Spring?

    • Answer: A prototype bean is a bean that is instantiated every time it's requested. This contrasts with singleton beans, which are instantiated only once.

46. How do you handle transactions in Spring?

    • Answer: Primarily using the @Transactional annotation, combined with a transaction manager (e.g., DataSourceTransactionManager).

47. What is the difference between XML configuration and annotation-based configuration in Spring?

    • Answer: XML configuration uses XML files to define beans, while annotation-based configuration uses annotations directly in the code. Annotation-based is generally preferred for its readability and maintainability.

48. What is the role of a `@Configuration` class in Spring?

    • Answer: A `@Configuration` class acts as a source of bean definitions. It uses `@Bean` methods to create and configure beans.

49. Explain the concept of aspect-oriented programming (AOP) and how it's used in Spring.

    • Answer: AOP allows separating cross-cutting concerns (e.g., logging, security) from core business logic. Spring AOP provides mechanisms for implementing this using proxies and aspects.

50. How does Spring handle exceptions in a web application?

    • Answer: Using `@ControllerAdvice` and `@ExceptionHandler` annotations to define global or specific exception handlers, providing centralized error handling.

51. What are some common use cases for Spring?

    • Answer: Building web applications, enterprise applications, microservices, batch processing applications, and integration solutions.

52. How does Spring support different databases?

    • Answer: Through Spring Data JPA or Spring JDBC, which are abstracted from the specific database implementation, allowing easy switching between databases with minimal code changes.

53. What are some best practices for using Spring?

    • Answer: Following consistent naming conventions, using dependency injection effectively, keeping beans loosely coupled, using proper transaction management, and writing unit tests.

54. How can you test Spring components?

    • Answer: Using unit testing frameworks like JUnit and Mockito, along with Spring's testing support (e.g., `@SpringBootTest`, `@MockBean`).

55. What are the advantages of using Spring over other Java frameworks?

    • Answer: POJO programming model, dependency injection, aspect-oriented programming, extensive community support, comprehensive features for various aspects of application development, and a large ecosystem of tools and libraries.

56. Explain Spring's role in microservices architecture.

    • Answer: Spring Boot simplifies the creation and deployment of microservices, providing lightweight and independent units of functionality. Spring Cloud provides tools for managing and orchestrating microservices.

57. How to configure Spring to use a different database (e.g., MySQL, PostgreSQL)?

    • Answer: By adding the appropriate database driver dependency and configuring the datasource properties in the application.properties or application.yml file. The specifics depend on whether using JPA or JDBC.

58. How to implement caching in Spring?

    • Answer: Using Spring's caching abstraction, typically with `@Cacheable`, `@CacheEvict`, `@CachePut` annotations, combined with a caching provider like EhCache or Redis.

59. What is the difference between `@RequestMapping` and `@GetMapping` annotations in Spring MVC?

    • Answer: `@RequestMapping` is a general-purpose annotation for handling HTTP requests, while `@GetMapping`, `@PostMapping`, `@PutMapping`, `@DeleteMapping`, etc., are specialized annotations for handling specific HTTP methods.

60. How to configure a scheduled task in Spring?

    • Answer: Using the `@Scheduled` annotation to mark a method to be executed at fixed intervals or cron expressions.

61. How to implement internationalization (i18n) in a Spring application?

    • Answer: By using Spring's message source mechanism, defining message properties files for different locales, and accessing messages using `MessageSource`.

62. Explain Spring's support for asynchronous programming.

    • Answer: Spring provides support for asynchronous method calls using the `@Async` annotation and an `AsyncConfigurer` implementation to configure an executor.

63. How to handle file uploads in a Spring MVC application?

    • Answer: Using the `MultipartFile` object in a controller method to access uploaded files, and handling file storage and processing as needed.

64. What is Spring WebFlux?

    • Answer: Spring WebFlux is a reactive web framework built on Project Reactor, providing a non-blocking, asynchronous approach to building web applications, suitable for high-throughput scenarios.

65. What are some common Spring Boot properties?

    • Answer: `server.port`, `spring.datasource.url`, `spring.jpa.hibernate.ddl-auto`, `logging.level.*`, etc.

66. How to profile a Spring application?

    • Answer: Using Spring profiles (e.g., `spring.profiles.active=dev`) to activate different configurations for different environments (development, testing, production).

67. What is Spring Cloud?

    • Answer: Spring Cloud provides tools for building distributed systems and microservices, including service discovery, configuration management, circuit breakers, and more.

68. How to secure a REST API with Spring Security?

    • Answer: By configuring Spring Security to protect specific endpoints, using authentication mechanisms (e.g., JWT, OAuth 2.0), and authorization rules to control access.

69. How to handle validation in Spring?

    • Answer: Using bean validation annotations (`@NotNull`, `@Size`, `@Email`, etc.) and the Hibernate Validator library.

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