Preparing for a Spring Boot interview can be a daunting task, but mastering common interview questions can significantly boost your confidence and performance. Spring Boot is a powerful framework that simplifies the development of Java-based enterprise applications. Knowing what to expect and how to answer will set you apart from other candidates. This guide provides you with 30 of the most frequently asked Spring Boot interview questions, complete with explanations, strategies, and example answers to help you ace your next interview.

What are Spring Boot Interview Questions?

Spring Boot interview questions are designed to assess your understanding of the Spring Boot framework, its core principles, and its practical applications. These questions cover a range of topics, including auto-configuration, dependency injection, Spring Boot starters, Actuator, and more. Interviewers use these questions to gauge your familiarity with the framework and your ability to apply it in real-world scenarios.

Why Do Interviewers Ask Spring Boot Questions?

Interviewers ask Spring Boot questions to evaluate several key competencies. They want to determine if you understand the fundamentals of Spring Boot and how it simplifies application development. They also assess your problem-solving skills and your ability to leverage Spring Boot features to build efficient, scalable, and maintainable applications. Additionally, interviewers aim to understand your experience with the Spring ecosystem and your ability to integrate Spring Boot with other technologies. By asking these questions, they can ascertain if you're the right fit for their team and project requirements.

Here's a quick list of the 30 questions we'll cover:

1. What is Spring Boot?

2. What are the advantages of using Spring Boot?

3. What are the key components of Spring Boot?

4. Why choose Spring Boot over Spring?

5. What is the starter dependency of the Spring Boot module?

6. How does Spring Boot work?

7. What is the difference between @RestController and @Controller in Spring Boot?

8. What is an IoC container?

9. Explain the flow of HTTPS requests through a Spring Boot application.

10. What is the difference between RequestMapping and GetMapping?

11. How can you change the port of the embedded Tomcat server in Spring Boot?

12. Can you create a non-web application in Spring Boot?

13. What is Spring Boot dependency management?

14. What are Spring Boot properties?

15. What are Spring Boot Starters?

16. What is Spring Boot Actuator?

17. What is Thymeleaf?

18. How to use Thymeleaf in a Spring Boot application?

19. How to connect Spring Boot to a database using JPA?

20. How to connect Spring Boot to a database using JDBC?

21. What is the @RestController annotation in Spring Boot?

22. What is Spring Data?

23. What is Spring Data JPA?

24. What is Spring MVC?

25. What is a Spring Bean?

26. What are Inner Beans in Spring?

27. What is Bean Wiring?

28. What are Spring Boot DevTools used for?

29. How to implement microservices architecture using Spring Boot?

30. How to implement distributed tracing in a Spring Boot application?

30 Spring Boot Interview Questions

1. What is Spring Boot?

Why you might get asked this:

Interviewers ask this question to assess your basic understanding of Spring Boot and its purpose. They want to know if you can clearly articulate what Spring Boot is and what problems it solves.

How to answer:

• Start by defining Spring Boot as a framework that simplifies the development of Spring applications.

• Explain that it provides convention-over-configuration, auto-configuration, and embedded servers.

• Mention that it makes it easy to build stand-alone, production-ready applications with minimal configuration.

Example answer:

"Spring Boot is a Java-based framework that simplifies the development of Spring applications. It offers features like convention-over-configuration, auto-configuration, and embedded servers such as Tomcat and Jetty. This allows developers to create stand-alone, production-ready applications with minimal configuration, reducing boilerplate code and setup."

2. What are the advantages of using Spring Boot?

Why you might get asked this:

This question is designed to evaluate your understanding of the benefits Spring Boot offers over traditional Spring development. Interviewers want to know if you appreciate the advantages that make Spring Boot a popular choice.

How to answer:

• Highlight advantages such as easy development and increased productivity.

• Mention minimal configuration and the elimination of XML configuration.

• Discuss the presence of embedded servers and the ease of deployment.

Example answer:

"Spring Boot offers several advantages, including simplified development, increased productivity, and minimal configuration. It eliminates the need for extensive XML configuration and provides embedded servers like Tomcat, making deployment straightforward. The auto-configuration feature reduces the amount of manual setup required, allowing developers to focus on business logic."

3. What are the key components of Spring Boot?

Why you might get asked this:

Interviewers ask this to gauge your knowledge of the core elements that make up Spring Boot. They want to see if you understand the fundamental building blocks of the framework.

How to answer:

• Identify Spring Boot auto-configuration as a key component.

• Mention Spring Boot CLI (Command Line Interface) for rapid application development.

• Discuss Spring Boot starter POMs (Project Object Model) for dependency management.

• Include Spring Boot Actuators for monitoring and management.

Example answer:

"The key components of Spring Boot include Spring Boot auto-configuration, which automatically configures the application based on the dependencies present. Spring Boot CLI allows for rapid application development, while Spring Boot starter POMs provide pre-configured dependency management. Additionally, Spring Boot Actuators offer monitoring and management capabilities for the application."

4. Why choose Spring Boot over Spring?

Why you might get asked this:

This question tests your understanding of the differences between Spring and Spring Boot and why Spring Boot is often preferred for modern application development.

How to answer:

• Explain that Spring Boot simplifies the development process compared to Spring.

• Highlight features like starter POMs, version management, and auto-configuration.

• Mention the convenience of embedded servers and actuators.

Example answer:

"Spring Boot simplifies the development process compared to Spring by offering features like starter POMs for easy dependency management, automatic version management, and auto-configuration. It also includes embedded servers, eliminating the need for external server setup, and actuators for monitoring and managing the application, making it a more convenient choice for modern development."

5. What is the starter dependency of the Spring Boot module?

Why you might get asked this:

Interviewers ask this to check your familiarity with Spring Boot's dependency management system and its ability to streamline project setup.

How to answer:

• List common starter dependencies such as Data JPA starter, Test Starter, and Security starter.

• Mention Web starter, Mail starter, and Thymeleaf starter as well.

• Explain that these starters bundle commonly used dependencies for specific functionalities.

Example answer:

"Common starter dependencies in Spring Boot include Data JPA starter for database access, Test Starter for testing support, Security starter for authentication and authorization, Web starter for building web applications, Mail starter for email functionality, and Thymeleaf starter for templating. These starters provide all the necessary dependencies for their respective functionalities, reducing the need for manual dependency management."

6. How does Spring Boot work?

Why you might get asked this:

This question is aimed at understanding your knowledge of the inner workings of Spring Boot, particularly how it automates the configuration process.

How to answer:

• Explain that Spring Boot automatically configures the application based on added dependencies using annotations.

• Mention the @SpringBootApplication annotation as the entry point.

• Describe how the main method starts the Spring application context.

Example answer:

"Spring Boot works by automatically configuring the application based on the dependencies added to the project. It uses annotations to streamline the configuration process. The entry point of a Spring Boot application is typically a class annotated with @SpringBootApplication, which also contains the main method that starts the Spring application context."

7. What is the difference between @RestController and @Controller in Spring Boot?

Why you might get asked this:

Interviewers ask this to assess your understanding of building web applications and APIs with Spring Boot, specifically how controllers handle requests and responses.

How to answer:

• Explain that @RestController returns data directly in the HTTP response as JSON or XML.

• Contrast this with @Controller, which maps the model object to a view or template.

• Highlight that @RestController is a combination of @Controller and @ResponseBody.

Example answer:

"@RestController and @Controller are both used for handling HTTP requests, but they differ in how they return responses. @RestController is used for building RESTful APIs and returns data directly in the HTTP response as JSON or XML. On the other hand, @Controller is typically used for traditional web applications and maps the model object to a view or template. Essentially, @RestController is a combination of @Controller and @ResponseBody."

8. What is an IoC container?

Why you might get asked this:

This question is designed to evaluate your understanding of the core principles of the Spring Framework, particularly Inversion of Control (IoC) and dependency management.

How to answer:

• Define IoC (Inversion of Control) as a design principle where the control of object creation and dependencies is inverted to the framework.

• Explain that an IoC container is a framework for automatic dependency injection.

• Mention that it manages object creation and lifetime.

Example answer:

"An IoC (Inversion of Control) container is a framework that implements the IoC principle, where the control of object creation and dependencies is managed by the container rather than the application code. It provides automatic dependency injection, managing the creation and lifetime of objects, which promotes loose coupling and improves maintainability."

9. Explain the flow of HTTPS requests through a Spring Boot application.

Why you might get asked this:

Interviewers ask this question to assess your understanding of how Spring Boot applications handle web requests and follow the MVC pattern.

How to answer:

• Explain that Spring Boot applications follow the MVC (Model-View-Controller) pattern.

• Describe how an HTTPS request is received by the controller.

• Mention that the request is processed, and then a response is sent back to the client.

Example answer:

"In a Spring Boot application, HTTPS requests are handled following the MVC pattern. When an HTTPS request is received, it is first routed to the appropriate controller. The controller processes the request, interacts with the model if necessary, and then generates a response, which is sent back to the client."

10. What is the difference between RequestMapping and GetMapping?

Why you might get asked this:

This question aims to evaluate your knowledge of Spring's request mapping annotations and how they are used to handle different HTTP methods.

How to answer:

• Explain that RequestMapping can handle multiple HTTP methods (GET, POST, PUT, etc.).

• Mention that GetMapping is specifically for GET requests.

• Highlight that GetMapping improves clarity by being more specific.

Example answer:

"RequestMapping and GetMapping are both used for mapping HTTP requests to controller methods, but they differ in scope. RequestMapping can handle multiple HTTP methods, such as GET, POST, PUT, and DELETE. In contrast, GetMapping is specifically designed for handling GET requests. Using GetMapping provides better clarity and specificity in the code, making it easier to understand the intended behavior."

11. How can you change the port of the embedded Tomcat server in Spring Boot?

Why you might get asked this:

Interviewers ask this to ensure you know how to configure basic server settings in Spring Boot, demonstrating your ability to customize the application environment.

How to answer:

• Explain that you can change the port by setting the server.port property.

• Mention that this property can be set in the application.properties file.

• Alternatively, it can be set in the application.yml file.

Example answer:

"You can change the port of the embedded Tomcat server in Spring Boot by setting the server.port property in the application.properties file or the application.yml file. For example, you can add the line server.port=8081 to change the port to 8081."

12. Can you create a non-web application in Spring Boot?

Why you might get asked this:

This question tests your understanding of Spring Boot's flexibility and its ability to be used for different types of applications beyond web applications.

How to answer:

• Answer "Yes" and explain that it is possible.

• Mention that you need to remove web dependencies.

• Explain that you need to adjust the application context creation.

Example answer:

"Yes, it is possible to create a non-web application in Spring Boot. To do this, you would need to remove the web dependencies from your project and adjust the application context creation to suit a non-web environment. This allows you to use Spring Boot for building console applications, batch processing jobs, and other types of non-web applications."

13. What is Spring Boot dependency management?

Why you might get asked this:

Interviewers ask this question to assess your understanding of how Spring Boot simplifies and automates the management of project dependencies.

How to answer:

• Explain that it automatically manages dependencies and configurations.

• Mention that it does this without specifying versions for dependencies.

• Highlight that it simplifies the build process and reduces compatibility issues.

Example answer:

"Spring Boot dependency management automatically manages the dependencies and configurations required for a Spring Boot application. It does this without the need to specify versions for individual dependencies, simplifying the build process and reducing potential compatibility issues. Spring Boot uses starter POMs to group related dependencies, making it easier to include the necessary libraries for specific functionalities."

14. What are Spring Boot properties?

Why you might get asked this:

This question is designed to evaluate your knowledge of how to configure and customize Spring Boot applications using properties.

How to answer:

• Explain that these are used to configure the application's behavior.

• Give examples such as server.port, spring.profiles.active, and spring.datasource.url.

• Mention that these properties can be set in application.properties or application.yml files.

Example answer:

"Spring Boot properties are used to configure various aspects of an application's behavior. Examples include server.port to configure the server port, spring.profiles.active to specify active profiles, and spring.datasource.url to configure the database connection URL. These properties can be defined in application.properties or application.yml files, allowing for easy customization of the application."

15. What are Spring Boot Starters?

Why you might get asked this:

Interviewers ask this question to assess your understanding of Spring Boot's starter dependencies and how they simplify project setup.

How to answer:

• Explain that they are pre-configured dependencies.

• Mention that they quickly enable common features in a project.

• Give examples such as spring-boot-starter-web or spring-boot-starter-data-jpa.

Example answer:

"Spring Boot Starters are pre-configured dependency bundles that quickly enable common features in a project. For example, spring-boot-starter-web includes all the dependencies needed to build a web application, such as Spring MVC, Tomcat, and Jackson. Similarly, spring-boot-starter-data-jpa includes the dependencies needed for JPA-based database access. These starters simplify project setup by providing a convenient way to include all the necessary dependencies for a specific functionality."

16. What is Spring Boot Actuator?

Why you might get asked this:

This question is aimed at evaluating your knowledge of Spring Boot's monitoring and management capabilities.

How to answer:

• Explain that it provides monitoring and management features for the application.

• Mention that it exposes health status, metrics, and environment variables.

• Highlight that it helps in monitoring and managing the application in a production environment.

Example answer:

"Spring Boot Actuator provides monitoring and management features for a Spring Boot application. It exposes endpoints that provide information about the application's health status, performance metrics, and environment variables. This helps in monitoring and managing the application in a production environment, allowing you to track its behavior and diagnose issues."

17. What is Thymeleaf?

Why you might get asked this:

Interviewers ask this question to assess your familiarity with templating engines commonly used in Spring applications for rendering dynamic web pages.

How to answer:

• Explain that it is a Java-based server-side template engine.

• Mention that it is used for rendering dynamic web pages in Spring applications.

• Highlight its natural templating capabilities.

Example answer:

"Thymeleaf is a Java-based server-side template engine used for rendering dynamic web pages in Spring applications. It offers natural templating capabilities, meaning that the templates can be opened in a browser and displayed as static HTML, which is helpful for designers. It integrates well with Spring and provides a flexible and powerful way to create dynamic web content."

18. How to use Thymeleaf in a Spring Boot application?

Why you might get asked this:

This question tests your practical knowledge of integrating Thymeleaf with Spring Boot for building dynamic web applications.

How to answer:

• Explain that you need to include the thymeleaf-spring-boot-starter dependency in your project.

• Mention that you can then create Thymeleaf templates in the templates directory.

• Highlight that you can use Spring MVC controllers to pass data to the templates.

Example answer:

"To use Thymeleaf in a Spring Boot application, you first need to include the thymeleaf-spring-boot-starter dependency in your project. Once you've added the dependency, you can create Thymeleaf templates in the templates directory. Spring MVC controllers can then be used to pass data to these templates, allowing you to render dynamic web pages with ease."

19. How to connect Spring Boot to a database using JPA?

Why you might get asked this:

This question is designed to evaluate your understanding of how to configure database connections in Spring Boot using Java Persistence API (JPA).

How to answer:

• Explain that you need to configure JPA properties.

• Mention that these properties are configured in the application.properties or application.yml file.

• Highlight properties such as spring.datasource.url, spring.datasource.username, and spring.datasource.password.

Example answer:

"To connect Spring Boot to a database using JPA, you need to configure the necessary JPA properties in the application.properties or application.yml file. This includes setting properties such as spring.datasource.url to specify the database URL, spring.datasource.username and spring.datasource.password for authentication, and spring.jpa.hibernate.ddl-auto to manage schema generation. Additionally, you'll need to include the spring-boot-starter-data-jpa dependency in your project."

20. How to connect Spring Boot to a database using JDBC?

Why you might get asked this:

Interviewers ask this question to assess your knowledge of configuring database connections in Spring Boot using Java Database Connectivity (JDBC).

How to answer:

• Explain that you need to configure JDBC properties.

• Mention that these properties are configured in the application.properties or application.yml file.

• Highlight properties such as spring.datasource.url, spring.datasource.username, and spring.datasource.password.

Example answer:

"To connect Spring Boot to a database using JDBC, you need to configure the JDBC properties in the application.properties or application.yml file. This includes setting properties such as spring.datasource.url to specify the database URL, spring.datasource.username and spring.datasource.password for authentication, and spring.datasource.driver-class-name to specify the JDBC driver class. You'll also need to include the appropriate JDBC driver dependency in your project."

21. What is the @RestController annotation in Spring Boot?

Why you might get asked this:

This question is aimed at evaluating your understanding of building RESTful web services using Spring Boot.

How to answer:

• Explain that it is used to create RESTful web services.

• Mention that it returns data directly in the HTTP response.

• Highlight that it is a combination of @Controller and @ResponseBody.

Example answer:

"The @RestController annotation in Spring Boot is used to create RESTful web services. It indicates that a class is a controller where every method returns a domain object instead of a view. It returns data directly in the HTTP response, typically in JSON or XML format. @RestController is essentially a combination of @Controller and @ResponseBody, making it convenient for building APIs."

22. What is Spring Data?

Why you might get asked this:

Interviewers ask this question to assess your understanding of Spring Data and how it simplifies data access in Spring applications.

How to answer:

• Explain that it is a framework that simplifies data-centric application development.

• Mention that it provides abstractions and utilities for various data sources.

• Highlight that it reduces the amount of boilerplate code needed for data access.

Example answer:

"Spring Data is a framework that simplifies data-centric application development by providing abstractions and utilities for various data sources, such as relational databases, NoSQL databases, and more. It reduces the amount of boilerplate code needed for data access by providing repositories, which automatically generate common data access methods based on the interface definition."

23. What is Spring Data JPA?

Why you might get asked this:

This question is designed to evaluate your knowledge of Spring Data JPA and its role in simplifying database access with JPA in Spring applications.

How to answer:

• Explain that it provides support for accessing relational databases using JPA.

• Mention that it simplifies data access by providing repositories.

• Highlight that it reduces the amount of boilerplate code needed for JPA operations.

Example answer:

"Spring Data JPA provides support for accessing relational databases using the Java Persistence API (JPA). It simplifies data access by providing repositories, which automatically generate common data access methods based on the interface definition. This significantly reduces the amount of boilerplate code needed for JPA operations, making it easier to interact with databases in Spring applications."

24. What is Spring MVC?

Why you might get asked this:

Interviewers ask this question to assess your understanding of Spring MVC and its role in building web applications.

How to answer:

• Explain that it is a web MVC framework for building web applications.

• Mention that it follows the Model-View-Controller pattern.

• Highlight that it provides a structured approach to building web applications.

Example answer:

"Spring MVC is a web framework for building web applications, following the Model-View-Controller (MVC) pattern. It provides a structured approach to building web applications by separating the application into three interconnected parts: the Model, which represents the data; the View, which presents the data to the user; and the Controller, which handles user input and updates the Model. This separation of concerns makes it easier to develop, test, and maintain web applications."

25. What is a Spring Bean?

Why you might get asked this:

This question is aimed at evaluating your understanding of the fundamental concept of a Spring Bean and its role in the Spring container.

How to answer:

• Explain that it is an object managed by the Spring IoC container.

• Mention that the container is responsible for creating, configuring, and managing the lifecycle of beans.

• Highlight that beans are the building blocks of a Spring application.

Example answer:

"A Spring Bean is an object that is managed by the Spring IoC container. The container is responsible for creating, configuring, and managing the lifecycle of these beans. Beans are the fundamental building blocks of a Spring application, and they are defined in the Spring configuration metadata, typically using XML configuration files or annotations."

26. What are Inner Beans in Spring?

Why you might get asked this:

Interviewers ask this question to assess your knowledge of advanced bean configuration options in Spring.

How to answer:

• Explain that they are beans defined within the scope of another bean's definition.

• Mention that they don't have their own IDs and are only accessible within the outer bean.

• Highlight that they are useful for defining dependencies that are only used by a single bean.

Example answer:

"Inner Beans in Spring are beans that are defined within the scope of another bean's definition. They do not have their own IDs and are only accessible within the outer bean. Inner beans are useful for defining dependencies that are only used by a single bean, helping to encapsulate and organize the configuration."

27. What is Bean Wiring?

Why you might get asked this:

This question is designed to evaluate your understanding of how dependencies are managed between beans in a Spring application.

How to answer:

• Explain that it is a mechanism for managing dependencies between beans.

• Mention that it allows Spring to inject collaborating beans into each other.

• Highlight that it can be done through XML configuration, annotations, or Java-based configuration.

Example answer:

"Bean Wiring is a mechanism for managing dependencies between beans in a Spring application. It allows Spring to inject collaborating beans into each other, establishing the relationships between them. Bean wiring can be done through XML configuration, annotations (such as @Autowired), or Java-based configuration, providing flexibility in how dependencies are managed."

28. What are Spring Boot DevTools used for?

Why you might get asked this:

Interviewers ask this question to assess your knowledge of tools that enhance development productivity in Spring Boot.

How to answer:

• Explain that they enhance development productivity.

• Mention features like automatic application restart and live reloading of static resources.

• Highlight that they make the development process more efficient.

Example answer:

"Spring Boot DevTools enhance development productivity with features like automatic application restart and live reloading of static resources. When DevTools detects changes in the classpath, it automatically restarts the application, and it also automatically refreshes the browser when static resources are modified. This makes the development process more efficient by reducing the need for manual restarts and refreshes."

29. How to implement microservices architecture using Spring Boot?

Why you might get asked this:

This question is designed to evaluate your understanding of how to leverage Spring Boot for building microservices-based applications.

How to answer:

• Explain that you can use Spring Cloud components.

• Mention components like Eureka for service discovery and Ribbon for load balancing.

• Highlight that Spring Boot simplifies the development and deployment of individual microservices.

Example answer:

"To implement a microservices architecture using Spring Boot, you can use Spring Cloud components such as Eureka for service discovery, Ribbon for client-side load balancing, and Spring Cloud Config for centralized configuration management. Spring Boot simplifies the development and deployment of individual microservices by providing auto-configuration, embedded servers, and easy dependency management. Each microservice can be developed as a separate Spring Boot application, allowing for independent deployment and scaling."

30. How to implement distributed tracing in a Spring Boot application?

Why you might get asked this:

Interviewers ask this question to assess your knowledge of monitoring and tracing techniques in distributed systems built with Spring Boot.

How to answer:

• Explain that you can use Spring Cloud Sleuth.

• Mention that you need to include the necessary dependencies.

• Highlight that you can integrate with tracing systems like Zipkin.

Example answer:

"To implement distributed tracing in a Spring Boot application, you can use Spring Cloud Sleuth by including the necessary dependencies in your project. Spring Cloud Sleuth automatically adds trace IDs to log messages and propagates them across service boundaries. You can then integrate with tracing systems like Zipkin or Jaeger to collect, store, and visualize the traces, allowing you to monitor and diagnose issues in a distributed environment."

Other Tips to Prepare for a Spring Boot Interview

To further prepare for your Spring Boot interview, consider the following tips:

• Review Spring Boot Documentation: Familiarize yourself with the official Spring Boot documentation to understand the framework's features and capabilities.

• Practice Coding: Work on personal projects or coding challenges to gain hands-on experience with Spring Boot.

• Understand Core Concepts: Ensure you have a solid understanding of core concepts like dependency injection, auto-configuration, and Spring Boot starters.

• Stay Updated: Keep up with the latest trends and updates in the Spring ecosystem to demonstrate your commitment to continuous learning.

• Prepare Examples: Have specific examples of projects or tasks where you've used Spring Boot to solve real-world problems.

By thoroughly preparing and understanding these common interview questions, you'll be well-equipped to impress your interviewers and land your dream job.

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FAQ

Q: What is the best way to prepare for a Spring Boot interview?

A: The best way to prepare is to understand the core concepts, practice coding, review the official documentation, and stay updated with the latest trends.

Q: Are Spring Boot interview questions difficult?

A: The difficulty level varies depending on the role and the company. However, with thorough preparation, you can confidently answer most questions.

Q: How important is it to know the Spring ecosystem for a Spring Boot interview?

A: It is crucial to have a good understanding of the Spring ecosystem, as Spring Boot builds upon it. Familiarity with concepts like Spring MVC, Spring Data, and Spring Security is highly beneficial.

Q: What are some common mistakes to avoid during a Spring Boot interview?

A: Common mistakes include not understanding the fundamentals, lacking practical experience, and not staying updated with the latest trends.