Springboot Interview Questions

Here are 20 top important Spring Boot interview questions every developer should prepare for:

1. What is Spring Boot? Why is it used?

• 
  Answer:
  Spring Boot is a framework designed to simplify the development of Java applications by eliminating boilerplate configurations. It provides features like auto-configuration, embedded servers, and starter dependencies for faster and easier application development.

2. What are the key features of Spring Boot?

• Auto-configuration of Spring components.


• Embedded servers like Tomcat, Jetty, and Undertow.


• Starter dependencies for preconfigured setups.


• Spring Boot Actuator for monitoring and management.


• Externalized configuration using application.properties or application.yml.

3. What is the purpose of the @SpringBootApplication annotation?

• 
  Answer:
  Combines:
  
  
  
  
  • 
    @Configuration: Marks the class as a configuration class.
  
  
  • 
    @EnableAutoConfiguration: Enables Spring Boot's auto-configuration.
  
  
  • 
    @ComponentScan: Scans the package for components.
  
  
  
  
  
  

4. What is the difference between Spring and Spring Boot?

• 
  Answer:
  
  
  
  
  • 
    Spring Framework: Requires manual configuration of beans, XMLs, and dependencies.
    
  
  
  • 
    Spring Boot: Provides auto-configuration, embedded servers, and opinionated defaults to simplify setup.
  
  
  
  
  
  

5. How do you configure a database connection in Spring Boot?

• 
  Answer:
  Add the following in application.properties:
  

  spring.datasource.url=jdbc:mysql://localhost:3306/mydb

  spring.datasource.username=root

  spring.datasource.password=password

  spring.jpa.hibernate.ddl-auto=update

Include the database driver dependency in your pom.xml.

6. How do you create a RESTful web service in Spring Boot?

• 
  Answer:
  Use @RestController to create endpoints. Example:
  

  @RestController

  @RequestMapping("/api")

  public class UserController {

      @GetMapping("/users")

      public List<String> getUsers() {

          return List.of("Alice", "Bob", "Charlie");

      }

  }

7. What are Spring Boot starters?

• 
  Answer:
  Starters are pre-configured dependencies for specific functionalities. Examples:
  
  
  
  
  • 
    spring-boot-starter-web: For web applications.
    
  
  
  • 
    spring-boot-starter-data-jpa: For JPA and Hibernate.
    
  
  
  • 
    spring-boot-starter-security: For Spring Security.
  
  
  
  
  
  

8. What is the Spring Boot Actuator?

• 
  Answer:
  A module for monitoring and managing applications in production. It provides endpoints like /actuator/health and /actuator/metrics.

9. How do you handle exceptions in Spring Boot?

• 
  Answer:
  Use @ControllerAdvice and @ExceptionHandler for global exception handling:
  

  @ControllerAdvice

  public class GlobalExceptionHandler {

      @ExceptionHandler(RuntimeException.class)

      public ResponseEntity<String> handleException(RuntimeException ex) {

          return new ResponseEntity<>("Error: " + ex.getMessage(), HttpStatus.INTERNAL_SERVER_ERROR);

      }

  }

10. What is the difference between @RestController and @Controller?

• 
  Answer:
  
  
  
  
  • 
    @RestController: Combines @Controller and @ResponseBody. It returns data (JSON/XML).
    
  
  
  • 
    @Controller: Used for building web pages (views).
  
  
  
  
  
  

11. What is Spring Data JPA?

• 
  Answer:
  A Spring module for simplifying data access using JPA. It provides repository interfaces like JpaRepository for common database operations.

12. What is the difference between CrudRepository and JpaRepository?

• 
  Answer:
  
  
  
  
  • 
    CrudRepository: Basic CRUD operations.
    
  
  
  • 
    JpaRepository: Extends CrudRepository and adds support for JPA-specific features like pagination and batch processing.
  
  
  
  
  
  

13. What is dependency injection, and how does Spring Boot implement it?

• 
  Answer:
  Dependency Injection (DI) is a design pattern where objects are injected into a class rather than being created within it. Spring Boot uses annotations like @Autowired to implement DI.

14. What are Spring Profiles?

• 
  Answer:
  Profiles allow you to define environment-specific configurations (e.g., dev, prod). Activate a profile using:
  

  spring.profiles.active=dev

15. How does Spring Boot implement security?

• 
  Answer:
  By adding the spring-boot-starter-security dependency, basic authentication is enabled by default. For custom security configurations, you can extend SecurityFilterChain or use WebSecurityConfigurerAdapter.

16. What is the purpose of the @Qualifier annotation?

• 
  Answer:
  Used to resolve ambiguity when multiple beans of the same type exist. Example:
  

  @Service

  public class MyService {

      @Autowired

      @Qualifier("beanName")

      private MyBean myBean;

  }

17. What is the use of @EnableAutoConfiguration?

• 
  Answer:
  It enables Spring Boot’s auto-configuration mechanism, scanning the classpath and configuring beans automatically based on the dependencies.

18. How does Spring Boot support microservices?

• 
  Answer:
  
  
  
  
  • Embedded servers for standalone deployment.
    
  
  
  • RESTful APIs for communication.
    
  
  
  • Integration with Spring Cloud for service discovery, configuration management, and circuit breaking.
  
  
  
  
  
  

19. How do you test a Spring Boot application?

• 
  Answer:
  Use Spring Boot Test features:
  
  
  
  
  • 
    @SpringBootTest: Loads the entire application context.
  
  
  • 
    @WebMvcTest: Tests only the web layer.
  
  
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    MockMvc: Simulates HTTP requests for testing controllers.
  
  
  
  
  
  

20. How do you externalize configuration in Spring Boot?

• 
  Answer:
  Store configurations in application.properties, application.yml, or external files. You can override them with environment variables or command-line arguments.