Spring Boot continues to be a must-have skill for backend Java developers. It simplifies Java development, helps you build microservices quickly, and supports everything from REST APIs to database management and cloud deployment.
Whether you’re a junior developer or an experienced engineer, preparing for Spring Boot interview questions is a smart move. This guide includes practical questions and answers, clearly explained for 2025 job interviews.
1. What is Spring Boot and how is it different from Spring Framework?
Spring Boot is a tool that helps you create stand-alone Java applications faster. It builds on top of the Spring Framework and removes the need for writing long configuration files. With Spring Boot, you can run apps directly with an embedded server like Tomcat or Jetty.
Unlike traditional Spring, you don’t need to configure everything manually. Spring Boot provides sensible defaults and ready-to-use starters for various modules like web, security, and data.
2. What are starter dependencies in Spring Boot?
Starter dependencies are pre-configured sets of libraries for different purposes. For example:
spring-boot-starter-web: For building REST APIsspring-boot-starter-data-jpa: For working with databases using JPAspring-boot-starter-security: For adding authentication and authorizationspring-boot-starter-test: For unit and integration testing
These starters reduce the effort of finding and adding the right dependencies one by one.
3. How does auto-configuration work in Spring Boot?
Spring Boot checks the classpath and automatically configures the application based on what it finds. If certain libraries are present, it sets up the necessary beans.
For example, if Spring Boot sees H2 database in the classpath, it configures a DataSource automatically. If you want to override the defaults, you can define your own beans.
Use the --debug flag to see which configurations are active.
4. What is the purpose of the @SpringBootApplication annotation?
@SpringBootApplication is a shortcut that combines three important annotations:
@Configuration: Marks the class as a source of bean definitions@EnableAutoConfiguration: Enables Spring Boot’s auto-configuration@ComponentScan: Scans for components in the current and sub-packages
It simplifies the setup by bringing all three together in one annotation.
5. What is Spring Boot Actuator?
Spring Boot Actuator provides production-ready features like monitoring, health checks, and metrics. You can use endpoints such as:
/actuator/health: Shows if the app is up and running/actuator/metrics: Displays performance stats/actuator/env: Shows environment variables
You can control which endpoints are exposed in the application.properties or application.yml.
6. How can you secure a REST API in Spring Boot?
Use Spring Security to protect your APIs. For example, you can allow public access to some endpoints while securing others:
@Bean
public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
return http
.authorizeHttpRequests(auth -> auth
.requestMatchers("/public/**").permitAll()
.anyRequest().authenticated())
.build();
}
You can use basic authentication, JWT, or OAuth2 depending on the requirements.
7. What is the difference between @Component, @Service, @Repository, and @Controller?
@Component: A general-purpose Spring bean@Service: Used in the service layer for business logic@Repository: Used in the data access layer and handles exceptions automatically@Controller: Used in MVC apps to handle web requests
All of them are registered as beans and picked up during component scanning.
8. How do you handle exceptions globally in Spring Boot?
Use @ControllerAdvice and @ExceptionHandler to catch and handle exceptions in one place:
@ControllerAdvice
public class GlobalExceptionHandler {
@ExceptionHandler(Exception.class)
public ResponseEntity<String> handleError(Exception ex) {
return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body("Something went wrong: " + ex.getMessage());
}
}
This helps return cleaner error messages from your APIs.
9. What is the use of application profiles in Spring Boot?
Application profiles let you define different configurations for different environments like dev, test, and prod.
spring.profiles.active=prod
You can then use files like application-dev.yml and application-prod.yml to manage separate settings for each environment.
10. How do you connect Spring Boot with a database?
Add the spring-boot-starter-data-jpa dependency. Then configure the database connection in application.properties:
spring.datasource.url=jdbc:mysql://localhost:3306/mydb spring.datasource.username=root spring.datasource.password=secret
Use @Entity to define your data model and extend JpaRepository to interact with the database.
11. How does Spring Boot support microservices?
Spring Boot works well with Spring Cloud to build distributed systems. It supports service discovery, centralized configuration, load balancing, circuit breakers, and more.
Common tools include:
- Eureka (Service registry)
- Config Server
- Spring Cloud Gateway
- Resilience4j for fault tolerance
12. How does Spring Boot handle scheduling?
Use the @EnableScheduling annotation in your main class and annotate methods with @Scheduled:
@Scheduled(fixedRate = 5000)
public void runTask() {
System.out.println("Running task every 5 seconds");
}
This is useful for background jobs and automated tasks.
13. What is Spring WebFlux?
Spring WebFlux is the reactive web framework in Spring Boot. It uses Reactor to handle non-blocking, asynchronous programming.
You can return types like Mono and Flux instead of traditional ResponseEntity.
This is ideal for high-performance applications with a large number of concurrent users.
14. What are some common annotations used in Spring Boot?
@SpringBootApplication@RestController@Autowired@Value@GetMapping,@PostMapping,@PutMapping,@DeleteMapping@RequestBody,@PathVariable,@RequestParam
Knowing when and how to use these annotations is key to building clean and maintainable apps.
15. How do you test a Spring Boot application?
Spring Boot provides spring-boot-starter-test, which includes JUnit, Mockito, and Spring Test.
Use @SpringBootTest for integration testing, and @WebMvcTest for testing controllers.
Mock beans and dependencies using @MockBean.
FAQs
Is Spring Boot good for beginners?
Yes, it simplifies setup and helps you start building apps quickly with less configuration.
Can I use Spring Boot without Spring Security?
Yes, but for production apps, adding security is highly recommended.
What are embedded servers in Spring Boot?
They are built-in servers like Tomcat or Jetty that allow you to run your app as a stand-alone JAR.
Is Spring Boot used in microservices?
Absolutely. It’s one of the most popular frameworks for building microservices.
Can I build REST APIs with Spring Boot?
Yes. It’s the easiest way to build RESTful services using @RestController.
