When preparing for a job in Java development, Spring Boot interview questions often become the center of discussion. This is because Spring Boot has simplified application development in the Java ecosystem, making it a favorite framework among developers and organizations. Employers use interviews not just to test theory, but also to understand how candidates apply Spring Boot concepts to solve real problems.

In this article, we will walk through the most common and insightful Spring Boot interview questions. These are explained in simple language so that anyone, from beginner to experienced professional, can understand and prepare effectively.

Introduction

Spring Boot is an open-source framework built on top of the Spring Framework. It eliminates boilerplate configurations and helps developers quickly build production-ready applications. The main focus of Spring Boot is convention over configuration, meaning most defaults are already provided, so developers spend less time on setup and more on writing business logic.

Because of its ease of use, Spring Boot has become essential knowledge for Java developers, which is why interviewers often ask specific questions about it.

Basic Spring Boot Interview Questions

1. What is Spring Boot?

Spring Boot is a Java framework that provides pre-configured settings to create stand-alone, production-ready applications with minimal code. It builds on the Spring framework but reduces the complexity of configuration.

2. How is Spring Boot different from Spring Framework?

Spring is a core framework that requires manual configuration for beans, dependencies, and web servers. Spring Boot, on the other hand, provides embedded servers, auto-configuration, and production-ready tools, reducing development effort significantly.

3. What is auto-configuration in Spring Boot?

Auto-configuration is a feature that automatically sets up beans and dependencies based on the project’s classpath. For example, if you add spring-boot-starter-web, Spring Boot automatically configures an embedded Tomcat server.

4. What are Spring Boot Starters?

Starters are pre-packaged sets of dependencies that make it easy to add common functionalities. For example, spring-boot-starter-data-jpa includes everything needed for JPA and Hibernate integration.

Advanced Spring Boot Interview Questions

5. What is the role of application.properties or application.yml?

These files are used to externalize configuration. Instead of hardcoding values, you place them in these files. For example, database credentials or port numbers are defined here, making the application flexible and easier to manage.

6. Explain Spring Boot Actuator.

Spring Boot Actuator provides production-ready features like health checks, metrics, and monitoring. It allows developers and system administrators to track the application’s performance and status in real time.

7. How does dependency injection work in Spring Boot?

Dependency injection in Spring Boot follows the same principles as in the Spring framework. The framework automatically provides required dependencies to a class, reducing the need for manual object creation. This is usually done with annotations like @Autowired or constructor injection.

8. What is the difference between @Component, @Service, and @Repository?

All three are stereotypes for Spring-managed beans, but each has a specific purpose:

• @Component: A general-purpose annotation for any bean.
  
• @Service: Marks a service class that holds business logic.
  
• @Repository: Indicates a data access class, adding extra functionality such as exception translation.
  

Real-World Spring Boot Interview Questions

9. How do you secure a Spring Boot application?

Spring Security is commonly used. It provides authentication, authorization, and protection against common vulnerabilities. Interviewers may also ask about JWT (JSON Web Tokens) or OAuth2 integration for more advanced scenarios.

10. How can you run a Spring Boot application?

A Spring Boot application can run in multiple ways:

• Using the main method with SpringApplication.run()
  
• Running mvn spring-boot:run (for Maven projects)
  
• Building a JAR and running with java -jar command
  

11. Can Spring Boot applications be deployed on external servers?

Yes. By default, Spring Boot uses an embedded server like Tomcat or Jetty. However, you can also package the application as a WAR file and deploy it to an external server.

12. What is the significance of profiles in Spring Boot?

Profiles allow you to define different configurations for different environments, such as development, testing, and production. For example, you may use an in-memory database for development but a MySQL database in production.

Commonly Asked Coding-Related Spring Boot Interview Questions

13. How do you connect a Spring Boot application to a database?

• Add the dependency spring-boot-starter-data-jpa.
  
• Define database credentials in application.properties.
  
• Create entities and repositories.
  Spring Boot automatically sets up Hibernate and connects to the database.
  

14. How do you expose a REST API in Spring Boot?

• Annotate the class with @RestController.
  
• Use @GetMapping, @PostMapping, or other mapping annotations to define endpoints.
  
• Run the application and access the endpoints via the embedded server.
  

15. How do you handle exceptions in Spring Boot?

Spring Boot provides @ControllerAdvice and @ExceptionHandler annotations to handle exceptions globally. This ensures consistent error responses across the application.

Advanced Level Questions Asked by Interviewers

16. What is Spring Boot CLI?

Spring Boot Command Line Interface (CLI) is a tool that allows developers to run and test Spring Boot applications using Groovy scripts without writing boilerplate code.

17. What are some common Spring Boot annotations?

• @SpringBootApplication
  
• @EnableAutoConfiguration
  
• @Configuration
  
• @Bean
  
• @RestController
  

18. What is caching in Spring Boot?

Caching improves performance by storing frequently accessed data in memory. Spring Boot supports caching with annotations like @Cacheable and @CacheEvict.

19. How do you monitor a Spring Boot application in production?

You can use Actuator endpoints, integrate with Prometheus, or connect with monitoring tools like Grafana, New Relic, or ELK stack.

20. How do you handle transactions in Spring Boot?

Spring Boot uses Spring’s @Transactional annotation to handle transactions. It ensures that a block of code either executes completely or rolls back in case of failure.

Practical Tips for Interview Preparation

1. Understand the basics – Do not just memorize answers. Be able to explain why certain features exist.
   
2. Practice coding – Implement small Spring Boot projects, like a REST API or CRUD application.
   
3. Learn deployment – Be ready to explain how to deploy to cloud platforms like AWS, Azure, or Docker.
   
4. Know the ecosystem – Understand how Spring Boot works with Spring Cloud, Microservices, and security frameworks.
   

Conclusion

Preparing for Spring Boot interview questions requires a mix of theoretical knowledge and practical experience. Interviewers often focus on your understanding of auto-configuration, dependency management, REST APIs, and security. At the same time, they may also test your ability to troubleshoot and optimize real-world applications.

By practicing the questions listed above and working on small projects, you can build the confidence needed to succeed in your next Spring Boot interview.