Top 25 Spring Boot Interview Questions and Answers
Are you preparing for a Spring Boot interview and want to ace it with confidence? You’re in the right place!
Spring Boot has become the go-to framework for building modern Java applications because of its simplicity, speed, and production-readiness. Whether you’re a beginner or an experienced developer brushing up your skills, understanding the core concepts of Spring Boot is crucial to crack technical interviews.
In this post, we’ve curated the Top 25 Spring Boot Interview Questions and Answers, each explained in a simple way with real-world examples. By the end, you’ll have a clear understanding of the important topics that interviewers frequently ask in Spring Boot interviews in 2024 and beyond.
Let’s dive right into it!
1. What is Spring Boot?
Spring Boot is a framework built on top of the Spring Framework to simplify Spring applications by removing boilerplate code and configurations.
Example:
Instead of manually configuring a DispatcherServlet, you just run a Spring Boot app, and it auto-configures it.
@SpringBootApplication
public class MyApp {
public static void main(String[] args) {
SpringApplication.run(MyApp.class, args);
}
}
2. How is Spring Boot different from Spring Framework?
- Spring: Heavy on configuration (XML/Java).
- Spring Boot: Convention over configuration. Auto-configuration and embedded servers.
3. What is @SpringBootApplication?
It’s a combination of:
- @Configuration
- @EnableAutoConfiguration
- @ComponentScan
Example:
@SpringBootApplication
public class DemoApplication { }
4. What is auto-configuration in Spring Boot?
Spring Boot automatically configures your application based on the libraries present.
Example:
If you have spring-boot-starter-data-jpa in your project, it auto-configures DataSource and EntityManager.
5. What are starters in Spring Boot?
Starters are dependency descriptors. They bundle commonly used libraries together.
Example:
- spring-boot-starter-web → Tomcat + Spring MVC + Jackson (JSON).
6. What is Spring Initializr?
It’s a web-based tool to bootstrap a Spring Boot project quickly.
7. Explain embedded servers in Spring Boot.
Spring Boot applications embed servers like Tomcat, Jetty, or Undertow.
Example:
You don’t need to deploy a WAR manually. The app runs with:
java -jar myapp.jar
8. How to change the default port in Spring Boot?
Modify application.properties:
server.port=8081
Or programmatically:
new SpringApplicationBuilder(MyApp.class)
.properties(“server.port=8081”)
.run(args);
9. What is application.properties / application.yml?
Configuration files where you define environment-specific properties.
Example:
spring.datasource.url=jdbc:mysql://localhost:3306/mydb
10. How do you create REST APIs in Spring Boot?
Use @RestController and @RequestMapping.
Example:
@RestController
@RequestMapping(“/api”)
public class HelloController {
@GetMapping(“/hello”)
public String sayHello() {
return “Hello World!”;
}
}
11. Difference between @RestController and @Controller?
- @Controller: Returns View (like JSP, Thymeleaf).
- @RestController: Returns JSON/XML directly.
12. How do you handle exceptions in Spring Boot?
Using @ControllerAdvice and @ExceptionHandler.
Example:
@ControllerAdvice
public class GlobalExceptionHandler {
@ExceptionHandler(Exception.class)
public ResponseEntity<String> handleException(Exception ex) {
return new ResponseEntity<>(“Error: ” + ex.getMessage(), HttpStatus.INTERNAL_SERVER_ERROR);
}
}
13. What are Profiles in Spring Boot?
Profiles allow configuring environment-specific beans and properties.
Example:
# application-dev.properties
server.port=8081
Run with:
–spring.profiles.active=dev
14. What is @ConfigurationProperties?
Used to map configuration properties to POJO classes.
Example:
@Component
@ConfigurationProperties(prefix = “app”)
public class AppConfig {
private String name;
}
app.name=MyApplication
15. What is Actuator in Spring Boot?
Spring Boot Actuator provides production-ready features like health checks, metrics, etc.
Example:
Add dependency:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
Access endpoints like /actuator/health.
16. How does Spring Boot implement security?
Using spring-boot-starter-security. By default, it secures all endpoints with basic authentication.
17. What is DevTools in Spring Boot?
DevTools improves development experience by enabling auto-restart, live reload, etc.
Example:
Add to pom.xml:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<scope>runtime</scope>
</dependency>
18. Explain the Spring Boot Application Lifecycle.
- SpringApplication.run()
- Create Spring Context
- Load configurations
- Start Embedded server
- Ready to accept requests
19. How to connect Spring Boot with databases?
Add starter:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
And configure in application.properties.
20. What is the difference between @Component, @Service, and @Repository?
All are stereotype annotations, but semantically:
- @Component: Generic
- @Service: Business logic
- @Repository: Database operations (with additional exception translation)
21. How do you create a custom Starter in Spring Boot?
- Create a new module
- Provide autoconfiguration class
- Provide spring.factories file under META-INF.
22. How does Spring Boot reduce boilerplate code?
- Auto Configuration
- Starter dependencies
- Embedded servers
- No XML configuration
23. Explain Lazy Initialization in Spring Boot.
Beans are initialized lazily when requested, not at application startup.
Enable Lazy Init:
spring.main.lazy-initialization=true
24. How to implement Caching in Spring Boot?
Enable caching with @EnableCaching and use @Cacheable on methods.
Example:
@Cacheable(“books”)
public Book getBookById(Long id) { }
25. What is the purpose of Spring Boot Dev Profile?
The dev profile is used for:
- Faster server restart
- In-memory DB (like H2)
- No production features enabled.
Mastering these Spring Boot interview questions and answers will not only boost your confidence but also help you demonstrate strong technical knowledge during your next Java/Spring Boot interview.
Remember, interviewers often look for candidates who understand both concepts and their practical applications — and that’s exactly what these examples help you achieve.
Keep practicing, build small projects, and stay updated with the latest features of Spring Boot.
If you found this list helpful, don’t forget to bookmark it and share it with others preparing for Spring Boot interviews!
Good luck with your interviews — you’ve got this!