Top 25 Spring Boot Interview Questions and Answers:

1. What is Spring Boot, and how does it differ from the Spring Framework?

Answer: Spring Boot is an opinionated framework that simplifies the development of Spring applications by providing defaults and convention-over-configuration. It eliminates the need for manual configuration and reduces boilerplate code.

2. How do you create a Spring Boot application?

Answer: You can create a Spring Boot application using Spring Initializr or by manually configuring the necessary dependencies and settings.

3. What are the advantages of using Spring Boot?

Answer: Advantages include simplified configuration, automatic dependency management, embedded servers, production-ready features, and seamless integration with other Spring projects.

4. How does Spring Boot achieve auto-configuration?

Answer: Spring Boot uses class path scanning and introspection to automatically configure beans based on the dependencies present in the class path.

5. How can you override default auto-configuration in Spring Boot?

Answer: You can use the @Conditional annotation to conditionally enable or disable auto-configuration for specific beans or components.

6. What is the purpose of the @RestController annotation?

Answer: @RestController is a specialized version of the @Controller annotation used for RESTful APIs. It combines @Controller and @ResponseBody.

7. How does Spring Boot handle externalized configuration?

Answer: Spring Boot supports various configuration sources like properties files, YAML files, environment variables, and command-line arguments.

8. What is Spring Data JPA, and how does it simplify data access in Spring Boot?

Answer: Spring Data JPA is a subproject of Spring that provides an abstraction layer over JPA for simplified data access and reduces boilerplate code.

9. What is the purpose of the application.properties (or application.yml) file in Spring Boot?

Answer: It is used to specify application-specific configurations like database settings, server port, logging levels, etc.

10. How can you enable caching in Spring Boot?

Answer: By adding the @EnableCaching annotation to the application's configuration class and configuring a caching provider.

11. What is Spring Boot Actuator?

Answer: Spring Boot Actuator provides built-in production-ready features like health checks, metrics, monitoring endpoints, and application management.

12. How can you handle exceptions in a Spring Boot application?

Answer: By using the @ExceptionHandler annotation to handle specific exceptions, or by implementing a custom exception handler using the @ControllerAdvice annotation.

13. What is the purpose of the @Autowired annotation?

Answer: @Autowired is used to inject dependencies automatically, reducing manual bean wiring in Spring applications.

14. How can you secure a Spring Boot application?

Answer: Spring Security provides authentication, authorization, and other security features to secure Spring Boot applications.

15. How can you schedule tasks in a Spring Boot application?

Answer: By using the @Scheduled annotation on a method, along with specifying the scheduling parameters like fixed rate, cron expression, etc.

16. How do you handle cross-origin resource sharing (CORS) in Spring Boot?

Answer: By adding the @CrossOrigin annotation to a controller method or globally configuring CORS using the WebMvcConfigurer interface.

17. What is the purpose of the Spring Boot Starter parent POM?

Answer: The Spring Boot Starter parent POM provides default configurations and dependency management for Spring Boot projects.

18. How can you handle file uploads in Spring Boot?

Answer: By using the MultipartFile class and the @RequestParam annotation to receive files in controller methods.

19. How can you implement database transactions in Spring Boot?

Answer: By using the @Transactional annotation on methods or classes that require transactional behavior.

20. How can you enable HTTPS in a Spring Boot application?

Answer: By configuring the server with an SSL certificate and enabling HTTPS in the application.properties or application.yml file.

21. What is the purpose of the SpringApplication.run() method in Spring Boot?

Answer: It is used to bootstrap and launch a Spring Boot application.

22. How can you handle internationalization (i18n) in Spring Boot?

Answer: By using message resource bundles and the Message Source interface for managing localized messages.

23. What is Spring Boot Actuator's health check endpoint used for?

Answer: It provides information about the application's health status, indicating if it is up and running or experiencing issues.

24. How can you deploy a Spring Boot application to a production environment?

Answer: Spring Boot applications can be deployed as standalone JAR files or as part of a WAR file to a web server or cloud platform.

25. How can you profile and optimize a Spring Boot application?

Answer: Spring Boot Actuator provides endpoints to monitor application metrics, including memory usage, CPU, and database queries. Tools like Visual and Profiler can be used for in-depth profiling and optimization.