Spring Boot Interview Questions & Answers (2025)

Spring Boot is a popular Java framework for building microservices and enterprise applications. Its auto-configuration, embedded servers, and starter dependencies make development faster and simpler. This guide covers 30 essential Spring Boot interview questions, with examples and explanations, suitable for both beginners and experienced developers.

1. What is Spring Boot?

Spring Boot is a framework built on top of Spring, designed to simplify application development. It provides auto-configuration, embedded servers, and starter dependencies.

@SpringBootApplication
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }
}

2. Difference between Spring and Spring Boot

3. What are Spring Boot Starters?

Starters simplify dependency management.

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

4. Explain Spring Boot Auto-Configuration

Spring Boot auto-configures beans based on dependencies in the classpath.

@Bean
public RestTemplate restTemplate() {
    return new RestTemplate();
}

5. What is @SpringBootApplication?

Combines:

• @Configuration

• @EnableAutoConfiguration

• @ComponentScan

@SpringBootApplication
public class MyApplication {}

6. Difference between @Component, @Service, @Repository, @Controller

7. What is Spring Boot Actuator?

Provides monitoring and metrics.

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

Access health: http://localhost:8080/actuator/health

8. External Configuration

application.properties or application.yml:

server.port=9090
spring.datasource.url=jdbc:mysql://localhost:3306/mydb
spring.datasource.username=root
spring.datasource.password=root

9. @Value Annotation

Injects properties:

@Value("${server.port}")
private int serverPort;

10. @RestController vs @Controller

11. Exception Handling

@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(Exception.class)
    public ResponseEntity<String> handleException(Exception e) {
        return new ResponseEntity<>(e.getMessage(), HttpStatus.INTERNAL_SERVER_ERROR);
    }
}

12. Spring Boot DevTools

Provides hot reload and automatic restart.

13. Spring Boot Profiles

Environment-specific configs:

spring.profiles.active=dev

14. Spring Boot Security

@Override
protected void configure(HttpSecurity http) throws Exception {
    http.authorizeRequests()
        .anyRequest().authenticated()
        .and().httpBasic();
}

15. @EnableAutoConfiguration vs @SpringBootApplication

• @EnableAutoConfiguration – auto-config only

• @SpringBootApplication – combines auto-config, component scan, configuration

16. Embedded Server

java -jar myapp.jar

17. Spring Boot CLI

Run Groovy scripts:

spring run hello.groovy

18. Database Connection

spring.datasource.url=jdbc:mysql://localhost:3306/mydb
spring.datasource.username=root
spring.datasource.password=root
spring.jpa.hibernate.ddl-auto=update

19. @Entity vs @Table

20. Spring Boot JPA Repositories

public interface UserRepository extends JpaRepository<User, Long> {}

21. Caching

@EnableCaching
@SpringBootApplication
public class MyApp {}

@Cacheable("users")
public User getUserById(Long id) { ... }

22. Scheduling

@EnableScheduling
@Scheduled(fixedRate = 5000)
public void runTask() { ... }

23. Testing

@SpringBootTest
class MyAppTests {
    @Test
    void contextLoads() {}
}

24. DevTools vs LiveReload

• DevTools: auto-restart

• LiveReload: browser refresh

25. Messaging

Supports Kafka, RabbitMQ:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-amqp</artifactId>
</dependency>

26. @RequestParam vs @PathVariable

27. File Upload

@PostMapping("/upload")
public String uploadFile(@RequestParam("file") MultipartFile file) { ... }

28. Thymeleaf Example

@Controller
public class MyController {
    @GetMapping("/home")
    public String home(Model model) {
        model.addAttribute("message", "Hello Spring Boot");
        return "home"; // home.html
    }
}

29. Spring Boot Starter POMs

• spring-boot-starter-web

• spring-boot-starter-data-jpa

• spring-boot-starter-security

30. Packaging

• JAR: java -jar target/myapp.jar

• WAR: Deploy to external server