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Spring Boot Interview Questions and Answers

1. What is Spring Boot?​

Spring Boot is a framework that simplifies the creation of production-ready applications with Spring. It provides auto-configuration, embedded servers, and opinionated defaults to reduce boilerplate code.

2. How does Spring Boot differ from Spring Framework?​

Spring Framework requires manual configuration of beans and dependencies. Spring Boot automates much of this with starters, auto-configuration, and embedded servers, making it easier to build standalone applications.

3. What are Spring Boot Starters?​

Starters are dependency descriptors that include a set of related libraries. For example, spring-boot-starter-web includes dependencies for web applications, reducing the need for manual Maven/Gradle configurations.

4. Explain auto-configuration in Spring Boot.​

Auto-configuration automatically configures Spring applications based on classpath dependencies. It scans for beans and applies defaults, which can be overridden by explicit configuration.

5. What is the purpose of the @SpringBootApplication annotation?​

It combines @Configuration, @EnableAutoConfiguration, and @ComponentScan. It marks the main class and enables Spring Boot's features like auto-configuration and component scanning.

6. How do you create a REST API in Spring Boot?​

Use @RestController and @RequestMapping annotations. For example:

@RestController
public class HelloController {
  @GetMapping("/hello")
  public String hello() {
    return "Hello, World!";
  }
}

7. What is the role of application.properties or application.yml?​

These files configure application settings like database connections, server ports, and logging levels. Spring Boot loads them automatically.

8. How does Spring Boot handle externalized configuration?​

It supports profiles (e.g., dev, prod) via application-{profile}.properties. Values can come from environment variables, command-line arguments, or external sources.

9. What is Spring Boot Actuator?​

Actuator provides production-ready features like health checks, metrics, and monitoring endpoints (e.g., /actuator/health) to inspect and manage applications.

10. How do you enable security in Spring Boot?​

Add spring-boot-starter-security dependency. It provides default authentication and can be customized with @EnableWebSecurity and configuration classes.

11. Explain Spring Boot's embedded server.​

Spring Boot includes Tomcat, Jetty, or Undertow by default. No need for external server deployment; applications run as JARs with java -jar.

12. What is the difference between @Component, @Service, and @Repository?​

  • @Component: Generic stereotype for any Spring-managed component.
  • @Service: Indicates a service layer component.
  • @Repository: Indicates a data access layer component, often with exception translation.

13. How do you handle exceptions in Spring Boot?​

Use @ControllerAdvice and @ExceptionHandler to create global exception handlers. For example:

@ControllerAdvice
public class GlobalExceptionHandler {
  @ExceptionHandler(Exception.class)
  public ResponseEntity<String> handleException(Exception e) {
    return ResponseEntity.status(500).body("Internal Server Error");
  }
}

14. What is Spring Boot DevTools?​

DevTools enhances development with features like automatic restarts, live reload, and remote debugging. Enabled by adding spring-boot-devtools dependency.

15. How do you test a Spring Boot application?​

Use @SpringBootTest for integration tests, which loads the full application context. For unit tests, use @WebMvcTest or @DataJpaTest for specific layers.