Introduction
Spring Boot is one of the most popular Java-based frameworks used for building microservices and enterprise-level applications. Its convention-over-configuration approach simplifies the development process, allowing developers to focus on business logic rather than boilerplate code.
As Spring Boot continues to dominate backend development, many companies include Spring Boot-related questions in their technical interviews. Whether you're a beginner or an intermediate developer, preparing for these questions can significantly improve your chances of landing a job.
This guide covers the top 30 Spring Boot interview questions and answers for beginners, categorized into fundamental, intermediate, and advanced levels. Each answer is explained in detail to ensure a thorough understanding.
1. Basic Spring Boot Interview Questions
1. What is Spring Boot?
Spring Boot is an open-source, Java-based framework designed to simplify the development of stand-alone, production-grade Spring applications. It provides:
Auto-configuration to reduce manual setup.
Embedded servers like Tomcat, Jetty, and Undertow.
Starter dependencies for easy project setup.
Production-ready features like health checks and metrics.
2. What are the advantages of using Spring Boot?
Rapid Development: Reduces boilerplate code.
Embedded Server: No need for external server deployment.
Auto-Configuration: Automatically configures Spring and third-party libraries.
Production-Ready: Includes monitoring, metrics, and externalized configuration.
Microservices Support: Ideal for building scalable microservices.
3. What is the difference between Spring and Spring Boot?
4. What is the use of the @SpringBootApplication annotation?
This annotation combines three annotations:
@Configuration: Marks the class as a configuration source.
@EnableAutoConfiguration: Enables Spring Boot’s auto-configuration.
@ComponentScan: Scans for Spring components in the current package.
Example:
java
@SpringBootApplication
public class MyApp {
public static void main(String[] args) {
SpringApplication.run(MyApp.class, args);
}
}
5. What are Spring Boot Starters?
Starters are dependency descriptors that bundle common libraries. Examples:
spring-boot-starter-web (for web applications)
spring-boot-starter-data-jpa (for JPA and Hibernate)
spring-boot-starter-test (for testing)
They reduce manual dependency management.
6. How does Spring Boot Auto-Configuration work?
Spring Boot scans the classpath and automatically configures beans based on:
Defined dependencies (e.g., spring-boot-starter-data-jpa configures DataSource).
Properties in application.properties or application.yml.
Custom configurations provided by developers.
7. How do you disable auto-configuration for a specific class?
Use @EnableAutoConfiguration(exclude = {DataSourceAutoConfiguration.class}) to exclude a specific auto-configuration class.
8. What is the default embedded server in Spring Boot?
Tomcat is the default embedded server, but Spring Boot also supports Jetty and Undertow.
9. How do you change the default port in Spring Boot?
Add this to application.properties:
properties
server.port=8081
10. What is Spring Boot Actuator?
Actuator provides production-ready features like:
Health checks (/actuator/health)
Metrics (/actuator/metrics)
Environment details (/actuator/env)
Enable it with spring-boot-starter-actuator.
2. Intermediate Spring Boot Interview Questions
11. What is Spring Boot DevTools?
DevTools provides developer-friendly features:
Automatic restart on code changes.
Live reload for static resources.
Property defaults for development.
12. How do you externalize configuration in Spring Boot?
Spring Boot supports:
application.properties / application.yml
Environment variables
Command-line arguments
@ConfigurationProperties for type-safe binding
13. What is the difference between @RestController and @Controller?
@Controller returns a view (for MVC apps).
@RestController (a combination of @Controller + @ResponseBody) returns JSON/XML responses (for REST APIs).
14. How do you handle exceptions in Spring Boot?
Use @ControllerAdvice for global exception handling:
java
@ControllerAdvice
public class GlobalExceptionHandler {
@ExceptionHandler(Exception.class)
public ResponseEntity<String> handleException(Exception e) {
return ResponseEntity.status(500).body("Error: " + e.getMessage());
}
}
15. What is Spring Data JPA?
Spring Data JPA simplifies database access by:
Reducing boilerplate code.
Providing CRUD operations out of the box.
Supporting custom queries via method naming conventions.
16. How do you connect Spring Boot to a database?
Configure application.properties:
properties
spring.datasource.url=jdbc:mysql://localhost:3306/mydb
spring.datasource.username=root
spring.datasource.password=root
spring.jpa.hibernate.ddl-auto=update
17. What is Hibernate in Spring Boot?
Hibernate is an ORM (Object-Relational Mapping) framework that maps Java objects to database tables. Spring Boot auto-configures Hibernate via spring-boot-starter-data-jpa.
18. What is Spring Security?
Spring Security provides authentication and authorization features. Enable it with spring-boot-starter-security.
19. How do you implement caching in Spring Boot?
Use @EnableCaching and @Cacheable:
java
@SpringBootApplication
@EnableCaching
public class MyApp {}
@Service
public class ProductService {
@Cacheable("products")
public Product getProductById(Long id) {
return productRepository.findById(id).orElse(null);
}
}
20. What is Spring Boot Testing?
Spring Boot provides:
@SpringBootTest for integration tests.
@WebMvcTest for controller tests.
@DataJpaTest for JPA repository tests.
3. Advanced Spring Boot Interview Questions
21. What is Spring Boot AOP?
Aspect-Oriented Programming (AOP) allows cross-cutting concerns (logging, security) to be modularized. Example:
java
@Aspect
@Component
public class LoggingAspect {
@Before("execution(* com.example.service.*.*(..))")
public void logBefore(JoinPoint joinPoint) {
System.out.println("Method called: " + joinPoint.getSignature());
}
}
22. How do you deploy a Spring Boot application?
Options:
JAR: mvn package → java -jar app.jar
WAR: Deploy to Tomcat/Jetty.
Docker: Containerize using Dockerfile.
23. What is Spring Cloud?
Spring Cloud provides tools for building distributed systems (microservices):
Service discovery (Eureka)
API Gateway (Zuul)
Distributed configuration (Spring Cloud Config)
24. How do you monitor Spring Boot apps?
Use:
Spring Boot Actuator for health checks.
Prometheus & Grafana for metrics.
ELK Stack for logging.
25. What is Spring Boot Profiles?
Profiles allow environment-specific configurations:
properties
# application-dev.properties
spring.datasource.url=jdbc:h2:mem:devdb
# application-prod.properties
spring.datasource.url=jdbc:mysql://prod-db:3306/mydb
Activate via --spring.profiles.active=dev.
26. How do you secure a Spring Boot REST API?
Use spring-boot-starter-security.
Configure JWT/OAuth2.
Enable HTTPS.
27. What is Spring Boot Batch?
A framework for batch processing (large datasets):
java
@Configuration
@EnableBatchProcessing
public class BatchConfig {
// Define Job, Step, Reader, Processor, Writer
}
28. How do you implement WebSockets in Spring Boot?
Use spring-boot-starter-websocket:
java
@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
@Override
public void configureMessageBroker(MessageBrokerRegistry config) {
config.enableSimpleBroker("/topic");
config.setApplicationDestinationPrefixes("/app");
}
}
29. What is Reactive Programming in Spring Boot?
Spring WebFlux supports non-blocking, reactive apps:
java
@RestController
public class ReactiveController {
@GetMapping("/flux")
public Flux<String> getFlux() {
return Flux.just("A", "B", "C");
}
}
30. How do you optimize Spring Boot performance?
Use caching (@Cacheable).
Enable GZIP compression.
Optimize database queries (indexing, lazy loading).
Use connection pooling (HikariCP).
FAQs
1. Is Spring Boot only for microservices?
No, it can be used for monolithic apps as well.
2. Can we use Spring Boot without Spring?
No, Spring Boot is built on top of Spring.
3. What databases does Spring Boot support?
MySQL, PostgreSQL, H2, MongoDB, etc.
4. How do you debug a Spring Boot app?
Use IDE debuggers or Actuator endpoints.
5. What is the latest Spring Boot version?
Check Spring Boot Releases.
6. How do you handle transactions in Spring Boot?
Use @Transactional on service methods.
7. Can Spring Boot work with frontend frameworks?
Yes (React, Angular, Thymeleaf).
8. What is Spring Boot CLI?
A command-line tool for rapid prototyping.
9. How do you log in Spring Boot?
Use SLF4J with Logback (default).
10. Is Spring Boot better than Node.js?
Depends on use cases (Java vs. JavaScript ecosystems).
Conclusion
Spring Boot is a powerful framework that simplifies Java development with features like auto-configuration, embedded servers, and production-ready tools. Mastering these top 30 Spring Boot interview questions will help beginners confidently tackle technical interviews.
For further learning, explore:
Hands-on projects (REST APIs, microservices).
Online courses (Udemy, Coursera).
Start building Spring Boot applications today and enhance your backend development skills!