Springboot Interview Questions

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

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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.

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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.

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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.

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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.

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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.

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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");
      }
  }

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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.

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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.

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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);
      }
  }

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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).

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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.

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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.

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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.

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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

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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.

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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;
  }

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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.

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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.

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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.
  • MockMvc: Simulates HTTP requests for testing controllers.

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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.

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