Here are some common Spring Boot interview questions and their answers for someone with 3 years of experience:

1. What is Spring Boot?

Answer: Spring Boot is an open-source framework that simplifies the development of Java applications. It provides a streamlined way to create stand-alone, production-grade Spring-based applications with minimal configuration.

2. What are the key features of Spring Boot?

Answer: Some key features of Spring Boot include:

1. Auto-configuration: It automatically configures Spring and third-party libraries based on project dependencies.
2. Embedded server: It provides a lightweight, embedded server (e.g., Tomcat, Jetty) for deploying applications.
3. Production-ready metrics: It offers various metrics, health checks, and monitoring options out of the box.
4. Spring Actuator: It provides endpoints for monitoring and managing the application.

3. How does Spring Boot simplify the configuration process?

Answer: Spring Boot follows the convention-over-configuration principle, which reduces the need for explicit configuration. It automatically configures components based on sensible defaults and allows customization through properties, annotations, and profiles.

4. Explain the concept of "Spring Boot Starter"?

Answer: Spring Boot Starters are a set of pre-configured dependencies that simplify the inclusion of common dependencies in Spring Boot applications. For example, the "spring-boot-starter-web" includes all the necessary dependencies for building web applications.

5. What is the purpose of the "application.properties" or "application.yml" file in Spring Boot?

Answer: These files are used for externalized configuration in Spring Boot. They allow you to define various properties that can be easily modified without changing the application code. The properties can be accessed using the @Value annotation or by using the Environment object.

6. How can you implement caching in Spring Boot?

Answer: Spring Boot provides integration with various caching providers like Ehcache, Redis, and Caffeine. You can enable caching by annotating methods with the @Cacheable annotation and configure the caching provider in the application configuration.

7. What is Spring Boot Actuator? How is it useful?

Answer: Spring Boot Actuator is a subproject of Spring Boot that provides production-ready monitoring and management endpoints for your application. It offers various endpoints to monitor health, metrics, logging, and more. Actuator is useful for gaining insight into the application's behavior and monitoring its health in a production environment.

8. How can you implement security in a Spring Boot application?

Answer: Spring Security is commonly used for implementing security in Spring Boot applications. You can configure security rules using annotations or by extending Spring Security classes. By adding the Spring Security dependencies and proper configuration, you can secure your application endpoints, implement authentication, and manage user roles and permissions.

Remember that these questions provide a starting point for your preparation. It's always a good idea to study the topics in more detail and be prepared to explain your practical experience and use cases during an interview. Good luck!