Spring Boot Interview Questions & Answers (2025)

Spring Boot is widely used for building enterprise-grade Java applications and microservices. This guide provides detailed explanations, examples, and ready-to-use code snippets for 30 frequently asked interview questions.

1. What is Spring Boot?

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

Features:

• Auto-configuration

• Embedded Tomcat, Jetty, or Undertow servers

• Starter dependencies for easy project setup

• Microservice-ready architecture

Example:

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@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 are pre-configured dependency sets to simplify dependency management.

Example:

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

Adds everything needed for building REST APIs: Spring MVC, Jackson, and embedded Tomcat.

4. Explain Spring Boot Auto-Configuration

Spring Boot automatically configures beans based on the classpath. This reduces manual configuration.

Diagram (text-based):

Dependencies -> AutoConfiguration -> Bean Creation -> Application Ready

Example:

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

5. What is @SpringBootApplication?

@SpringBootApplication is a meta-annotation combining:

• @Configuration – Marks class as a configuration

• @EnableAutoConfiguration – Enables auto-configuration

• @ComponentScan – Scans components automatically

Example:

@SpringBootApplication
public class MyApplication {}

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

7. What is Spring Boot Actuator?

Explanation:
Provides production-ready features like monitoring, metrics, and health checks.

Example:

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

Access health endpoint:

http://localhost:8080/actuator/health

8. How to Externalize Configuration in Spring Boot

Spring Boot supports application.properties or application.yml.

Example:

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

9. What is @Value Annotation?

Injects values from configuration files.

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

10. Difference between @RestController and @Controller

11. How to handle exceptions in Spring Boot

Explanation: Use @ControllerAdvice and @ExceptionHandler to handle global exceptions.

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

12. What is Spring Boot DevTools?

Provides hot reload and automatic restart for development.

Dependency:

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

13. What are Profiles in Spring Boot?

Profiles allow environment-specific configurations.

Example:

# application-dev.properties
server.port=8081

Activate:

spring.profiles.active=dev

14. Spring Boot Security

Provides authentication and authorization using spring-boot-starter-security.

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

15. Difference between @EnableAutoConfiguration and @SpringBootApplication

• @EnableAutoConfiguration: Enables auto-configuration only

• @SpringBootApplication: Combines auto-configuration, component scan, and configuration

16. Embedded Server in Spring Boot

Spring Boot provides embedded servers, so no WAR deployment needed.

Run standalone app:

java -jar myapp.jar

17. Spring Boot CLI

Run Spring Boot apps from the command line using Groovy scripts:

spring run hello.groovy

18. Connect Spring Boot to a Database

Example: MySQL with JPA

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

@Entity
public class User {
    @Id @GeneratedValue private Long id;
    private String name;
}

19. Difference between @Entity and @Table

20. Spring Boot JPA Repositories

Automatically implements CRUD operations.

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

21. Caching in Spring Boot

@EnableCaching
@SpringBootApplication
public class MyApp {}

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

22. Scheduling in Spring Boot

@EnableScheduling
@SpringBootApplication
public class MyApp {}

@Scheduled(fixedRate = 5000)
public void runTask() {
    System.out.println("Task executed every 5 seconds");
}

23. Testing in Spring Boot

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

24. DevTools vs LiveReload

• DevTools: Auto-restarts application

• LiveReload: Refreshes browser automatically

25. Spring Boot Messaging

Supports Kafka and 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) {
    // handle file
}

28. Spring Boot with Thymeleaf

@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 – REST API

• spring-boot-starter-data-jpa – Database access

• spring-boot-starter-security – Security

30. Packaging Spring Boot Applications

• JAR: Standalone executable

mvn clean package
java -jar target/myapp.jar

• WAR: Deployable on external server