Spring Boot has become a must-know framework for any Java developer, especially if you are preparing for interviews. It simplifies Java application development by handling boilerplate code, offering embedded servers, and providing ready-to-use starter dependencies. With Spring Boot, you can set up web applications, REST APIs, or microservices quickly and efficiently.
Whether you are a beginner or experienced developer, interviewers often test both your theoretical knowledge and practical experience with Spring Boot. This guide lists 50 frequently asked Spring Boot interview questions with detailed, human-friendly answers. Reading through them will help you feel confident and prepared for your next interview.
50 Spring Boot Interview Questions with Answers
1. What is Spring Boot?
Spring Boot is a framework built on top of Spring that makes it easy to create standalone, production-ready applications. It eliminates a lot of configuration work, provides embedded servers like Tomcat, and includes starter dependencies to quickly set up common functionality.
2. What is the use of @SpringBootApplication?
It’s a convenience annotation that combines @Configuration, @EnableAutoConfiguration, and @ComponentScan. Essentially, it tells Spring Boot to scan for components and automatically configure your application.
3. How does Spring Boot differ from the Spring Framework?
Unlike traditional Spring, where you manually configure beans and servers, Spring Boot provides auto-configuration, embedded servers, and starter dependencies. It allows you to get applications running quickly without spending hours on setup.
4. What are Spring Boot Starters?
Starters are pre-built dependency packages that bring in all the libraries you need for a particular feature. For example, spring-boot-starter-web includes Spring MVC, Jackson, and an embedded Tomcat server, so you don’t have to add each dependency manually.
5. What is Spring Boot CLI?
The CLI lets you run Spring Boot applications using Groovy scripts. It’s a handy tool for quickly testing ideas without setting up a full project.
6. What is an embedded server in Spring Boot?
Embedded servers like Tomcat or Jetty allow you to run applications without installing a separate server. This makes deploying and running your app much simpler.
7. What is Spring Boot Initializr?
Spring Initializr is an online tool to quickly generate Spring Boot projects. You can select dependencies, Java version, and build tools, and it gives you a ready-to-use project template.
8. What is auto-configuration in Spring Boot?
Auto-configuration automatically sets up your Spring application based on the dependencies in your project. For example, if Spring Boot sees a JPA dependency, it will automatically configure a database connection and EntityManager.
9. What is Spring Boot Actuator?
Actuator gives you endpoints to monitor and manage your app. You can check health, metrics, beans, and environment properties, which is especially useful in production.
10. Why use application.properties or application.yml?
These files store configuration settings like database URLs, ports, logging levels, or API keys. Externalizing configuration keeps your code flexible and environment-independent.
11. What are Spring Boot Profiles?
Profiles let you define different configurations for environments like dev, test, and prod. You can switch between them easily by setting the active profile.
12. Common Spring Boot annotations
Some frequently used ones include @RestController, @GetMapping, @PostMapping, @Autowired, @Service, and @Repository.
13. What is Spring Boot DevTools?
DevTools provides live reload, auto-restart, and other development-time features, so you don’t have to restart the app manually after each change.
14. What is Spring Boot Security?
It integrates Spring Security and allows you to secure your apps with authentication and authorization, often with minimal configuration.
15. How do you create REST APIs in Spring Boot?
Use @RestController to define your API endpoints and annotations like @GetMapping or @PostMapping to handle requests. Combine with service and repository layers for clean architecture.
16. Spring Boot starter dependencies for database
Common examples: spring-boot-starter-data-jpa, spring-boot-starter-jdbc, spring-boot-starter-data-mongodb.
17. How does Spring Boot support microservices?
You can build independent, self-contained services with Spring Boot. Using Spring Cloud, these services can register with Eureka, discover other services, handle configuration centrally, and remain resilient under failure.
18. How do you handle exceptions in Spring Boot?
Use @ControllerAdvice and @ExceptionHandler to define global exception handling logic, which keeps your code clean and consistent.
19. Difference between @Component, @Service, and @Repository
@Component is generic, @Service is for business logic, and @Repository is specifically for database access and provides exception translation.
20. How do you implement logging in Spring Boot?
Spring Boot uses SLF4J with Logback by default. You can configure logging levels in application.properties and create custom log formats if needed.
21. What are Spring Boot metrics?
Metrics are statistics like request counts, response times, memory usage, and database queries, accessible via Actuator endpoints.
22. Best practices for performance optimization
Use caching, optimize database queries, monitor memory and CPU usage, and avoid unnecessary dependencies.
23. How do you test Spring Boot applications?
Use @SpringBootTest for integration testing, @MockBean for mocking, and JUnit or Mockito for unit tests.
24. Conditional annotations
@ConditionalOnProperty or @ConditionalOnClass allow beans to load only if certain conditions are met.
25. Securing REST APIs
You can use JWT, OAuth2, or basic authentication with Spring Security.
26. What is Spring Boot’s support for scheduling tasks?
Use @EnableScheduling and @Scheduled for running periodic or delayed tasks.
27. How do you connect Spring Boot with a database?
Configure DataSource in application.properties and use JPA repositories or JDBC templates.
28. How to manage transactions in Spring Boot?
Use @Transactional on service methods to handle transactions automatically.
29. What is Spring Boot’s approach to configuration management?
It supports application.properties, application.yml, environment variables, and Spring Cloud Config for centralized configuration.
30. How do you deploy Spring Boot applications?
Spring Boot applications can be packaged as JAR or WAR files and deployed to cloud platforms, containers, or on-premise servers with embedded servers.
31. What is Spring Boot Starter Test?
A starter dependency that includes libraries like JUnit, Mockito, Hamcrest, and Spring Test for unit and integration testing.
32. What is the difference between @RestController and @Controller?
@RestController combines @Controller and @ResponseBody, used for REST APIs. @Controller is used for MVC applications and returns views.
33. What is the role of Spring Boot AutoConfiguration Report?
It helps debug auto-configuration by showing which configurations are applied or skipped during startup.
34. What is Spring Boot’s lazy initialization?
It delays bean creation until needed, improving startup time in large applications.
35. How do you externalize configuration in Spring Boot?
Using application.properties, application.yml, environment variables, or command-line arguments.
36. How do you implement caching in Spring Boot?
Using @EnableCaching and annotations like @Cacheable, @CachePut, and @CacheEvict.
37. What is Spring Boot’s support for messaging?
It supports Kafka, RabbitMQ, JMS, and other messaging services for asynchronous communication.
38. What is Spring Boot’s support for internationalization (i18n)?
It allows creating locale-specific messages using messages.properties and the MessageSource interface.
39. How do you monitor application memory and threads in Spring Boot?
Actuator endpoints like /actuator/metrics, /actuator/heapdump, and JMX integrations help monitor memory, threads, and CPU usage.
40. What is Spring Boot’s support for file uploads?
Using MultipartFile in controllers, configured via spring.servlet.multipart properties.
41. How do you configure multiple datasources in Spring Boot?
By defining multiple DataSource beans and marking one as primary, along with JPA entity managers for each datasource.
42. How do you implement REST API versioning in Spring Boot?
Through URI versioning (/api/v1/resource), request parameters, or headers like Accept-version.
43. How do you enable HTTPS in Spring Boot?
By configuring a keystore with server.ssl.* properties in application.properties and redirecting HTTP to HTTPS if needed.
44. What is the difference between @EnableAutoConfiguration and @SpringBootApplication?
@SpringBootApplication includes @EnableAutoConfiguration along with @ComponentScan and @Configuration.
45. What is Spring Boot WebFlux?
It’s a reactive programming framework for building non-blocking, asynchronous web applications.
46. How do you create custom Spring Boot starter dependencies?
By creating a Maven or Gradle project with the required dependencies and proper auto-configuration.
47. What are Spring Boot Actuator health indicators?
Endpoints that provide health checks for databases, disk space, messaging queues, or custom checks.
48. What is the difference between JPA and Hibernate in Spring Boot?
Hibernate is an implementation of JPA, which is a specification for ORM in Java applications.
49. How do you configure logging in Spring Boot?
Using application.properties with logging.level.* and integrating Logback or Log4j configurations.
50. How do you integrate Spring Boot with Docker?
By creating a Dockerfile, building the Spring Boot JAR, and running it inside a container with the necessary environment variables.
Wrapping Up
Spring Boot has become a cornerstone for modern Java development, allowing you to build applications faster and with less hassle. By understanding these 50 spring boot interview questions and their answers, you can confidently explain both the core concepts and practical applications of Spring Boot. Focus on hands-on experience with REST APIs, microservices, configuration management, and testing to demonstrate your expertise. Preparing with these spring boot interview questions not only strengthens your interview performance but also improves your ability to work efficiently in real-world projects. Keep practicing, explore real examples, and you’ll be ready to impress any interviewer.
Frequently Asked Questions (FAQs)
Q1. What is the difference between Spring Boot and Spring MVC?
Spring MVC is used to build web apps but needs a lot of setup. Spring Boot makes it easier by automatically configuring things and providing ready-to-use tools, so you can start faster.
Q2. Can Spring Boot work with databases other than MySQL?
Yes. Spring Boot works with many databases like PostgreSQL, Oracle, SQL Server, MongoDB, and Redis. You just need to add the right dependency and set up the connection.
Q3. How do you secure REST APIs in Spring Boot?
You can protect your APIs using Spring Security. Common ways include using JWT tokens, OAuth2, or simple username/password login. Spring Boot makes this setup easier.
Q4. Can you run a Spring Boot app without installing a server?
Yes. Spring Boot comes with embedded servers like Tomcat or Jetty, so you can run the app directly as a JAR file without installing a separate server.
Q5. What does Spring Boot Actuator do?
Actuator helps you check the health and performance of your app. You can see things like memory usage, active threads, and other stats to make sure your app is running well. This is also a common topic in spring boot interview questions.
