Introduction to Spring Boot Interview Questions

       

1. What is Spring Boot? How does it differ from the Spring Framework?

• Answer: Spring Boot is an opinionated framework built on top of the Spring Framework, designed to simplify the development of production-ready applications with minimal configuration. It provides default configurations and eliminates boilerplate code, whereas the Spring Framework requires more manual setup and configuration.

2. Explain the key features of Spring Boot.

• Answer:
  • Auto-configuration: Automatically configures beans based on classpath settings, reducing manual configuration.
  • Standalone: Embeds servlet containers like Tomcat, Jetty, or Undertow, allowing applications to run independently.
  • Production-ready: Built-in features for monitoring, health checks, and externalized configuration.
  • Opinionated defaults: Provides defaults that can be overridden with minimal effort.
  • Spring Boot starters: Pre-configured dependencies to simplify project setup.

3. How does Spring Boot achieve auto-configuration?

• Answer: Spring Boot achieves auto-configuration by scanning the classpath for specific libraries and dependencies. It uses conditions to determine which beans to instantiate based on the environment and existing configurations. Developers can also override auto-configurations by providing their own configurations.

4. What are Spring Boot starters? Give examples.

• Answer: Spring Boot starters are a set of convenient dependency descriptors that you can include in your application. They allow you to add dependencies for common functionalities with a single entry, reducing the need to manually manage dependencies. Examples include spring-boot-starter-web for web applications, spring-boot-starter-data-jpa for JPA-based data access, and spring-boot-starter-security for security configurations.

5. Explain the role of @SpringBootApplication annotation.

• Answer: @SpringBootApplication is a meta-annotation that combines three annotations:
  • @Configuration: Indicates that the class contains Spring Bean configurations.
  • @ComponentScan: Enables component scanning to automatically discover and register Spring beans.
  • @EnableAutoConfiguration: Enables Spring Boot's auto-configuration mechanism.

6. How does Spring Boot support externalized configuration?

• Answer: Spring Boot supports externalized configuration through properties files (application.properties or application.yml), environment variables, and command-line arguments. It prioritizes configuration sources in a specific order, allowing developers to override defaults easily without modifying the application's code.

7. What is Spring Boot Actuator? What endpoints does it expose?

• Answer: Spring Boot Actuator provides production-ready features to monitor and manage applications. It exposes endpoints such as /health (application health check), /metrics (application metrics), /info (application information), /env (environment properties), and /actuator (root endpoint for all Actuator endpoints).

8. How can you deploy a Spring Boot application?

• Answer: Spring Boot applications can be deployed in various ways:
  • Standalone JAR: Package the application as an executable JAR file using Maven or Gradle, and run it using java -jar.
  • WAR file: Deploy the application to a servlet container like Tomcat or Jetty by packaging it as a WAR file.
  • Docker container: Containerize the application using Docker and deploy it to container orchestration platforms like Kubernetes.

9. What are some best practices for testing Spring Boot applications?

• Answer:
  • Use @SpringBootTest to load the entire application context for integration testing.
  • Mock dependencies using @MockBean for unit testing.
  • Use @WebMvcTest or @DataJpaTest for testing specific layers of the application.
  • Use tools like JUnit, Mockito, and AssertJ for writing and executing tests.

10. How does Spring Boot support microservices architecture?

• Answer: Spring Boot supports microservices architecture by providing:
• Embedded servers: Allows each microservice to run independently.
• Spring Cloud: Provides tools for service discovery, configuration management, and distributed tracing.
• Spring Boot Actuator: Monitors and manages microservices in production environments.
• Spring Boot starters: Simplifies dependency management and configuration for microservices.

1. How does Spring Boot manage application properties?

   • Answer: Spring Boot uses application.properties or application.yml files to externalize configuration. Properties can also be configured using environment variables and command-line arguments, with properties precedence defined by the order of configuration sources.

2. Explain the use of @Value annotation in Spring Boot.

   • Answer: @Value annotation in Spring Boot injects values from properties files or environment variables into fields in Spring-managed beans. Example: @Value("${myapp.property}") private String myProperty;

3. How can you override Spring Boot default configurations?

   • Answer: Default configurations in Spring Boot can be overridden by providing custom configurations in application properties or YAML files, or by using @Configuration annotated classes to define specific beans or configurations.

Real-Time Features in Spring Boot

4. What is Spring Boot DevTools? How does it improve development workflow?

   • Answer: Spring Boot DevTools provides enhanced development experience by enabling features like automatic restarts, LiveReload support for browser refresh, and enhanced logging for quicker debugging during development.

5. Explain Spring Boot Actuator and its importance in real-time monitoring.

   • Answer: Spring Boot Actuator exposes operational endpoints such as /health, /metrics, and /info to monitor and manage the application in real-time. It provides insights into application health, metrics, and configuration properties, aiding in operational visibility and troubleshooting.

6. How can you implement caching in Spring Boot applications?

   • Answer: Spring Boot supports caching through annotations like @Cacheable, @CachePut, and @CacheEvict from the spring-boot-starter-cache starter. Caching improves application performance by storing frequently accessed data in memory.

Swagger Integration in Spring Boot

7. What is Swagger? How does it facilitate API documentation in Spring Boot?

   • Answer: Swagger is a tool that simplifies API documentation and testing. In Spring Boot, Swagger can be integrated using libraries like springfox-swagger2 and springfox-swagger-ui. It generates API documentation automatically from annotations (@Api, @ApiOperation) in your controllers.

8. How do you enable Swagger UI in a Spring Boot application?

   • Answer: To enable Swagger UI in Spring Boot, you typically:
     • Add dependencies (springfox-swagger2 and springfox-swagger-ui) in pom.xml or build.gradle.
     • Configure Swagger beans (Docket bean) in a @Configuration class to customize Swagger documentation settings.

9. Explain the purpose of @ApiModel and @ApiModelProperty annotations in Swagger.

   • Answer: @ApiModel is used to describe a model class for Swagger documentation, while @ApiModelProperty annotates fields within the model to provide additional metadata (e.g., description, data type) for Swagger UI.