Top 50 Questions for Spring Boot Interview

Spring Boot has become a popular framework for building enterprise-level Java applications. Its simplicity, scalability, and ease of integration make it an essential skill for developers. If you’re preparing for a Spring Boot interview, this comprehensive guide will help you navigate the most frequently asked questions and topics. Let’s dive in!

Top 50 Questions for Spring Boot Interview For Fresher and Experience Candidates

1. Basics of Spring Boot – Top 50 Questions for Spring Boot Interview

1. What is Spring Boot?
   • Spring Boot is an extension of the Spring framework that simplifies the development of stand-alone, production-grade Spring applications.
2. What are the main features of Spring Boot?
   • Auto-configuration
   • Embedded servers (Tomcat, Jetty, Undertow)
   • Opinionated defaults
   • Starter dependencies
3. How does Spring Boot differ from Spring Framework?
   • Spring Boot simplifies configuration, provides embedded servers, and has pre-configured templates, while Spring Framework requires extensive configuration.
4. What are Starter dependencies in Spring Boot?
   • Starters are pre-configured dependencies that simplify Maven/Gradle configurations, e.g., spring-boot-starter-web.
5. Explain the concept of auto-configuration in Spring Boot.
   • Auto-configuration in Spring Boot reduces manual setup by automatically configuring application components based on included dependencies.

2. Spring Boot Annotations

6. What is the use of @SpringBootApplication?
   • It combines @Configuration, @EnableAutoConfiguration, and @ComponentScan.
7. What does @RestController annotation do?
   • Combines @Controller and @ResponseBody, simplifying RESTful services.
8. What is the purpose of @RequestMapping?
   • Maps HTTP requests to handler methods in controllers.
9. Differentiate between @GetMapping, @PostMapping, @PutMapping, and @DeleteMapping.
   • They are specialized annotations for mapping HTTP GET, POST, PUT, and DELETE requests, respectively.
10. What is @EnableAutoConfiguration?
    • Enables Spring Boot’s auto-configuration mechanism.

3. Configuration and Properties

11. What is the difference between application.properties and application.yml?
    • Both are configuration files; .properties uses key-value pairs, while .yml uses hierarchical data.
12. How do you define custom properties in Spring Boot?
    • Add key-value pairs in application.properties or application.yml, then use @Value or @ConfigurationProperties to bind them.
13. What is the purpose of the spring.profiles.active property?
    • Specifies the active profile (e.g., dev, test, prod).
14. How can you externalize configuration in Spring Boot?
    • Using environment variables, command-line arguments, or external property files.
15. What is the role of @ConfigurationProperties?
    • Maps properties defined in configuration files to POJOs.

4. Spring Boot DevTools

16. What is Spring Boot DevTools?
    • A module that enables hot-reloading, automatic browser refresh, and other developer-friendly features.
17. How do you enable live reload with DevTools?
    • Add spring-boot-devtools dependency to your project.
18. Does DevTools work in production?
    • No, it is disabled in production to avoid performance overhead.

5. Embedded Servers

19. What embedded servers does Spring Boot support?
    • Tomcat, Jetty, and Undertow.
20. How do you change the default port of a Spring Boot application?
    • Set server.port property in application.properties or application.yml.
21. How can you deploy a Spring Boot application to an external server?
    • Package it as a WAR file and deploy it to a servlet container like Apache Tomcat.

6. Spring Boot Actuator

22. What is Spring Boot Actuator?
    • Provides production-ready features like monitoring, metrics, and health checks.
23. What are some of the endpoints provided by Actuator?
    • /actuator/health, /actuator/info, /actuator/metrics
24. How do you secure Actuator endpoints?
    • Use Spring Security or configure access control in application.properties.
25. Can you customize Actuator endpoints?
    • Yes, by enabling or disabling specific endpoints and changing their base path.

7. Spring Boot Security Top 50 Questions for Spring Boot Interview

26. How do you secure a Spring Boot application?
    • Add Spring Security dependency and configure authentication and authorization.
27. What is the default username and password in Spring Security?
    • Default username is user, and the password is auto-generated and logged at startup.
28. How do you customize the login page in Spring Security?
    • Use HttpSecurity.formLogin() to specify a custom login page.
29. What is the purpose of @EnableWebSecurity?
    • Enables Spring Security’s web security support.
30. How do you implement role-based access control in Spring Boot?
    • Use annotations like @PreAuthorize and configure roles in HttpSecurity.

8. Spring Boot Testing

31. What testing frameworks are supported by Spring Boot?
    • JUnit, TestNG, Mockito, Spring Test.
32. What is @SpringBootTest?
    • Used for integration testing; loads the complete application context.
33. What is the use of @MockBean?
    • Creates a mock of a bean and injects it into the application context.
34. Explain the role of @Test annotation.
    • Marks a method as a test case.
35. How do you test REST endpoints in Spring Boot?
    • Use MockMvc or TestRestTemplate.

9. Spring Boot JPA and Hibernate Questions for interview

36. What is Spring Data JPA?
    • A Spring module that simplifies data access by providing JPA-based repositories.
37. What is the purpose of @Entity annotation?
    • Maps a class to a database table.
38. What is the role of @Id and @GeneratedValue annotations?
    • @Id specifies the primary key, and @GeneratedValue defines the generation strategy for IDs.
39. How do you define a repository in Spring Data JPA?
    • Extend JpaRepository or CrudRepository.
40. What is the difference between save() and saveAndFlush()?
    • save() saves the entity; saveAndFlush() saves and immediately flushes changes to the database.

10. Advanced Topics Top 50 Questions for Spring Boot Interview

41. What is Spring Boot CLI? Top 50 Questions for Spring Boot Interview
    • A command-line tool for creating Spring Boot applications.
42. What is the purpose of @EnableAsync?
    • Enables asynchronous method execution.
43. How do you implement caching in Spring Boot?
    • Add caching dependencies and annotate methods with @Cacheable or @CacheEvict.
44. What is Spring Cloud?
    • A set of tools for building distributed systems.
45. Explain the concept of Circuit Breaker in Spring Boot.
    • Used to prevent cascading failures by breaking the circuit when a service is down.

11. Microservices with Spring Boot

46. How do you create a microservice using Spring Boot?
    • Use Spring Boot with Spring Cloud and RESTful APIs.
47. What is Eureka in Spring Boot?
    • A service discovery tool used in microservices architecture.
48. What is Spring Boot Zuul?
    • A gateway service for routing and filtering requests.
49. How do you handle inter-service communication in microservices?
    • Using REST, gRPC, or message brokers like RabbitMQ.
50. What is Feign Client?
    • A declarative HTTP client used for inter-service communication.

12. Miscellaneous Top 50 Questions for Spring Boot Interview

51. How do you handle exceptions in Spring Boot?
    • Use @ControllerAdvice and @ExceptionHandler.
52. What are Spring Boot starters?
    • Predefined dependencies for specific functionalities.
53. How do you monitor a Spring Boot application?
    • Use Actuator, Prometheus, or external tools like Grafana.
54. What is a WebClient in Spring Boot?
    • A non-blocking, reactive HTTP client.
55. What is a CommandLineRunner?
    • An interface used to execute code at application startup.

Top 50 Questions for Spring Boot Interview

Top 50 Questions for Spring Boot Interview : These questions provide a strong foundation for Spring Boot interviews. Make sure to dive deeper into each topic and understand the underlying concepts. Practical experience with real-world projects will also boost your confidence and readiness for any Spring Boot interview.

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