Top Spring Boot Interview Questions and Answers

Here are top Spring Boot interview questions,

1. What is Spring Boot, and what problem does it solve?

Spring Boot is an open-source Java-based framework used to create stand-alone, production-grade Spring-based applications with minimal configuration. It simplifies the setup and development of Spring applications by providing defaults for many configuration parameters and enabling developers to create applications quickly.

 

2. Explain the advantages of using Spring Boot.

Spring Boot offers several advantages:

   - Simplified configuration and setup.

   - Built-in support for common application features like embedded servers.

   - Automatic dependency management through Spring Boot Starter.

   - Production-ready features like metrics, health checks, and externalized configuration.

 

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

Spring is a comprehensive framework for building enterprise applications, while Spring Boot is an extension of the Spring framework that simplifies the setup and development of Spring applications. Spring Boot provides defaults for many configuration parameters and offers built-in features like an embedded web server.

 

4. Explain the Spring Boot Starter.

A Spring Boot Starter is a dependency management approach that simplifies the inclusion of common sets of dependencies in your project. It's a way to provide pre-configured templates for specific tasks, such as web development, data access, and more. Starters help developers focus on application logic rather than worrying about dependency conflicts.

 

5. What is an Embedded Container in Spring Boot?

Spring Boot includes embedded containers like Tomcat, Jetty, and Undertow, which can run web applications without requiring an external web server. Developers can package these containers along with their application, making it easy to create self-contained, executable JAR files.

 

6. Explain the purpose of the `application.properties` or `application.yml` file.

These configuration files allow you to configure various aspects of your Spring Boot application, such as database settings, server port, logging levels, and more. They provide a way to externalize configuration, making it easy to customize application behavior without modifying the code.

 

7. What is Spring Boot Auto-Configuration?

Spring Boot Auto-Configuration automatically configures beans and components based on the dependencies present in the classpath. It simplifies application setup by providing sensible defaults and reducing the need for manual configuration.

 

8. What is the difference between `@Component`, `@Service`, and `@Repository` in Spring Boot?

These are all stereotypes used to define Spring beans:

   - `@Component`: General-purpose stereotype for any Spring-managed component.

   - `@Service`: Indicates that a class is a service and should be picked up during classpath scanning.

   - `@Repository`: Indicates that a class is a repository, typically for database access, and enables exception translation.

 

9. Explain the Spring Boot Actuator.

Spring Boot Actuator is a set of production-ready features that help you monitor and manage your application. It includes endpoints for health checks, metrics, application info, and more. Actuator is useful for monitoring the application's health and performance in production environments.

 

10. What is the purpose of the `@SpringBootApplication` annotation?

`@SpringBootApplication` is a combination of three annotations: `@Configuration`, `@EnableAutoConfiguration`, and `@ComponentScan`. It's used to mark the main class of a Spring Boot application and enables auto-configuration and component scanning.

 

11. Explain the role of the Spring Boot DevTools.

Spring Boot DevTools is a set of tools aimed at improving developer productivity. It provides features like automatic application restart, live reloading of changed resources, and enhanced property file support during development.

 

12. What is the difference between a SpringApplication and a regular Java `main` method?

`SpringApplication` is a class provided by Spring Boot to bootstrap a Spring application. It loads the application context, runs the embedded container, and provides various configuration options. Using `SpringApplication` is recommended for Spring Boot applications over a regular `main` method.

 

13. How do you enable CORS (Cross-Origin Resource Sharing) in a Spring Boot application?

You can enable CORS in a Spring Boot application by using the `@CrossOrigin` annotation at the controller level or by configuring CORS globally using a `CorsFilter` bean or by configuring it in the `application.properties` or `application.yml` file.

 

14. What is Spring Boot Data JPA, and why is it useful?

Spring Boot Data JPA is a subproject of Spring Boot that simplifies data access with the Java Persistence API (JPA). It provides a way to interact with databases using high-level repository interfaces and auto-generates queries, reducing the need for boilerplate code.

 

15. Explain the concept of Spring Boot Profiles.

Spring Boot Profiles allow you to define different configurations for different environments (e.g., development, testing, production) or specific use cases. By using profiles, you can tailor your application's behavior and configuration for different scenarios.

 

16. What is Spring Boot Security, and how can you configure it?

Spring Boot Security is a powerful framework for securing Spring applications. You can configure it by adding dependencies, defining security rules, and configuring authentication providers. It provides features like user authentication, authorization, and protection against common security vulnerabilities.

 

17. What is Spring Boot Test, and how do you write unit tests for a Spring Boot application?

Spring Boot Test is a set of testing utilities provided by Spring Boot for writing tests. You can write unit tests using JUnit or TestNG along with annotations like `@SpringBootTest` to load the Spring context, `@MockBean` to mock components, and `@DataJpaTest` for testing data access components.

 

18. Explain the purpose of the Spring Boot CommandLineRunner interface.

`CommandLineRunner` is an interface in Spring Boot used to execute code after the Spring application context has been initialized. It's often used to perform tasks like data initialization or running custom logic when the application starts.

 

19. How can you secure sensitive information like passwords or API keys in a Spring Boot application?

Sensitive information can be secured using Spring Boot's property encryption or by using external configuration providers like environment variables, secret management tools, or dedicated configuration servers like Spring Cloud Config Server.

 

20. What is Spring Boot Actuator's `/info` endpoint used for?

The `/info` endpoint provided by Spring Boot Actuator is used to expose custom application information. Developers can use this endpoint to provide details about the application's version, build information, or any other custom data they want to expose.

 

Above are few top Spring Boot interview questions. Remember to prepare and expand on these answers.

Good luck with your interview! 👍