Spring Boot Interview Questions and Answers

CTA

In today’s technology-driven world, Spring Boot has become an integral part of web development in building robust and scalable applications. As the demand for skilled Spring Boot developers soars, it’s essential to be well-prepared for the interview process. Ace the spring Boot Technical Interview with this set of questions covering all the Fundamentals from basic to advanced.

Below are the three categories into which these SpringBoot interview questions are divided:

1. Basic Level Spring Boot Interview Questions

2. Intermediate Level Spring Boot Interview Questions

3. Advanced Level Spring Boot Interview Questions

Basic Level Spring Boot Interview Questions

1. What is Spring Boot, and what are its key advantages?

Spring Boot is a robust framework that simplifies the development of Java applications by providing a streamlined and opinionated approach. It aims to minimize the required configuration and setup, allowing developers to focus more on writing business logic than dealing with boilerplate code.

Its key advantages include:

• Easy Setup: Spring Boot eliminates manual configuration with sensible defaults, allowing developers to start coding immediately.
• Rapid Development: It provides built-in features and starter templates for quick prototyping and development of web applications, REST APIs, and microservices.
• Production-Ready: Spring Boot promotes best practices, offering built-in support for monitoring, health checks, and metrics to facilitate smooth deployment and management in production environments.
• Dependency Management: It simplifies dependency management by providing a curated set of dependencies that work well together. It also enhances code modularity and testability through dependency injection and inversion of control.
• Community Support: Spring Boot has an active community that provides extensive documentation, tutorials, and forums for developers to seek help and share knowledge.

2. What are the Starter Dependencies?

Starter Dependencies in Spring Boot are curated dependencies designed to enable developers to quickly and easily add shared libraries and frameworks into their applications, providing essential functionality such as web development, database connectivity, security, etc. By including one, Spring Boot automatically configures and sets up the required components and dependencies, thereby streamlining the development process.

3. How do I connect the Spring Boot application to a database using JDBC?

To connect a Spring Boot application to a database using JDBC, you must:

1. Include the JDBC Starter Dependency in your project’s pom.xml file.
2. Configure the database connection details, such as the URL, username, and password, in the application’s configuration file (application.properties or application.yml).
3. Use the appropriate JDBC APIs, such as JdbcTemplate or EntityManager, to interact with the database and execute SQL queries.

4. What is Thymeleaf, and how to use it?

Thymeleaf is a popular Java-based template engine used for server-side rendering in Spring Boot applications. It provides a simple and natural way to generate dynamic HTML content by seamlessly integrating with the Spring ecosystem.

To use Thymeleaf in a Spring Boot application, you must include the Thymeleaf Starter Dependency in your project’s pom.xml file. Then, you can create HTML templates with Thymeleaf syntax, such as using expressions and tags to dynamically render data and logic within your web pages.

5. How does a Spring Boot application get started?

A Spring Boot application starts by executing the main method in the application’s entry point class. The entry point class is typically annotated with @SpringBootApplication, which combines several annotations like @Configuration, @EnableAutoConfiguration, and @ComponentScan. The @SpringBootApplication annotation sets up the Spring Boot application context, initializes necessary components, and begins the application’s lifecycle.

6. What are the steps to deploy Spring Boot web applications as JAR and WAR files?

To facilitate the deployment of a Spring Boot web application, simply include the following:

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
</plugin>

With this plugin, the package phase will generate a JAR file encompassing all essential libraries, dependencies, and even an embedded server. Consequently, the application can be effortlessly executed as a standard JAR file, ensuring seamless functionality.

Similarly, when aiming to construct a Web Application Archive(WAR) file, it is imperative to specify the packaging element within the project’s configuration file. By including the <packaging>war</packaging> tag, you can indicate your intention to generate a WAR file successfully. This step is crucial for ensuring the proper deployment and functioning of your web application.

Spring Boot provides an embedded server to make JAR file deployment a simple matter; just build your application as a JAR file, which includes an embedded server (e.g., Tomcat) to run your web app, and use java -jar to open it up for execution.

To deploy as a WAR file, your project should be configured to create one instead of producing JARs. Change the Packaging element in Pom.xml from JAR to War and configure all relevant dependencies and servlet mappings as appropriate before uploading the WAR file onto Tomcat or Jetty for deployment.

7. How do you create a Spring Boot project using the Boot CLI?

To use the Spring Boot CLI, first, install it on your system. When ready, open a command prompt and use spring init along with any desired project name or dependencies (for instance, to create a basic Spring Boot project, use spring init myproject –dependencies=web).

8. How can we create a custom endpoint in the Spring Boot Actuator?

To create a custom endpoint in Spring Boot Actuator, you need to define a new @RestController or @Controller class and map it to the desired endpoint URL using @RequestMapping or other relevant annotations. 

Within the custom endpoint class, you can define methods to handle requests and provide the necessary logic or data to be exposed through the Actuator endpoint. Additionally, you may need to configure any necessary security or authorization settings to control access to the custom endpoint.

9. What is the role of Starter Dependencies in Spring Boot? Give an example.

Starter Dependencies in Spring Boot are like ready-to-use toolkits that simplify dependency management. They come bundled with all the necessary libraries for specific functionalities, making it a breeze to kickstart development. 

For example, “spring-boot-starter-web” is like a magic box containing everything needed to build web applications effortlessly, saving developers from the tedious task of manually handling individual dependencies. It’s like having a shortcut that allows developers to dive straight into coding without worrying about intricate dependency configurations.

10. What is the significance of the Spring Boot Actuator? Name a few common endpoints it provides.

The Spring Boot Actuator module significantly provides production-ready features for monitoring and managing Spring Boot applications. It offers valuable endpoints to retrieve information about the application’s health, configuration, metrics, and more. 

Common endpoints include /health for health status, /info for general application information, /metrics for application metrics, /env for environment details, /configprops for configuration properties, and /actuator as the root endpoint for all Actuator-related endpoints. Actuator empowers developers and administrators with insights into application behavior, facilitating effective monitoring and management of Spring Boot applications.

Intermediate Level Spring Boot Interview Questions

11. Explain the ‘convention over configuration’ concept of ‘convention over configuration’ in Spring Boot.

The “convention over configuration” concept of “convention over configuration” in Spring Boot emphasizes that developers should follow predefined conventions rather than specifying explicit configurations for every aspect of an application. By adhering to these conventions, Spring Boot can automatically configure many aspects, reducing the need for manual setup and allowing developers to focus on application logic. This approach promotes simplicity, reduces boilerplate code, and accelerates development.

12. What is an IOC container?

An Inversion of Control(IOC) container is a core concept in the Spring framework that manages the creation and life cycle of objects. It allows the framework to control the flow of application execution by injecting dependencies into objects rather than the objects creating their dependencies. The IOC container facilitates loose coupling, modularity, and easier application testing.

13. How do you configure Log4j for logging?

To configure Log4j for logging in to a Spring Boot application, you must include the Log4j dependency in your project’s build configuration (e.g., pom.xml for Maven). Then, create a Log4j configuration file (e.g., log4j2.xml or log4j.properties) to specify logging levels, appenders, and other settings. Place this configuration file in the classpath of your application, and Log4j will automatically use it for logging.

14. What are the differences between JPA and Hibernate?

The differences between JPA and Hibernate are:

15. Describe the flow of HTTPS requests through the Spring Boot application.

The flow of HTTPS requests through a Spring Boot application typically involves the following steps:

• The client sends an HTTPS request to the Spring Boot application over a secure connection (HTTPS).
• The request is received by the Spring Boot application’s embedded servlet container (e.g., Tomcat, Jetty). The container’s SSL/TLS implementation handles the decryption of the HTTPS request and verifies the client’s certificate (if required).
• The request is passed to the appropriate Spring MVC controller based on the request mapping and routing configuration.
• The controller processes the request, performs any necessary business logic, and generates a response.
• The response is encrypted and sent back to the client over a secure HTTPS connection.

16. How to enable HTTP/2 support in Spring Boot?

To enable HTTP/2 support in a Spring Boot app, take these steps:

• Add any dependencies necessary for HTTP/2 support, such as spring-boot-starter-tomcat or spring-boot-starter-jetty, which should provide support.
• Configure your embedded servlet container so it uses an HTTP/2-capable version of Tomcat or Jetty.
• Make sure that your app is only served over HTTPS; HTTP/2 only supports secured connections.
• Start the Spring Boot application, which will become accessible using the HTTP/2 protocol.

17. What annotations are used to create an Interceptor?

The annotations used to create an Interceptor in Spring Boot are:

• @Component or a related stereotype annotation to mark the interceptor class as a Spring Bean.
• @Override on the preHandle, postHandle, and afterCompletion methods in the interceptor class to override the corresponding methods of the HandlerInterceptor interface.
• @Order to specify the order in which the interceptor should be executed if you have multiple interceptors.
• @Interceptor (optional) to explicitly declare the class as an interceptor, which is helpful in some frameworks or configurations.

18. What is a Swagger in Spring Boot?

Swagger in Spring Boot is an API documentation and generation tool that provides a way to visually represent, interact with, and document RESTful APIs without needing manual documentation.

Swagger provides developers with a user-friendly interface (the Swagger UI) that enables them to explore API endpoints and input/output parameters, as well as execute requests directly from it.

In Spring Boot, it can be integrated using either the springfox or springdoc-openapi libraries alongside relevant annotations in their code to describe API operations and models. Swagger makes API development faster while improving collaboration and understanding among developers and consumers of APIs alike.

19. What are the different ways to configure a Spring Boot application?

Spring Boot offers multiple ways to configure applications:

• Application properties or YAML files for customizing various aspects
• Environment variables for runtime configuration
• Command-line arguments to override default values
• Configuration classes are annotated with @Configuration for programmatic configuration
• Profiles for environment-specific configurations
• Custom configuration properties for type-safe configuration
• Integration with Spring Cloud Config for centralized configuration management. These options provide flexibility to configure Spring Boot applications according to specific needs and preferences

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

To enable Cross-Origin Resource Sharing (CORS) in a Spring Boot application, you can use the @CrossOrigin annotation at the controller level to allow specific origins, methods, and headers. 

Alternatively, you can configure CORS globally by creating a CorsConfiguration bean or implementing a WebMvcConfigurer to define custom mappings and configurations. External configuration properties can also be utilized. These approaches ensure the secure handling of cross-origin requests and provide flexibility to customize CORS settings according to your application’s requirements.

Advanced Level Spring Boot Interview Questions

21. Explain the concept of profiles in Spring Boot and how they can be used.

Profiles in Spring Boot enable the customization of application behavior based on different environments or deployment scenarios. By defining profiles, developers can configure environment-specific properties, select different component implementations, customize beans, and conditionally load application parts.

Profiles are activated using the spring.profiles.active property in the configuration file or command-line arguments. This allows for streamlined configuration management and adaptability, ensuring the application can seamlessly adapt to various environments and meet specific requirements.

22. How does Spring Boot simplify the development process compared to traditional Spring?

Spring Boot simplifies development compared to traditional Spring by providing automatic configuration, starter dependencies, embedded servers, opinionated defaults, production-ready features, and enhanced developer tools. 

It eliminates the need for extensive XML configurations and reduces manual setup. With pre-configured starter dependencies, developers can quickly include the required functionality. 

The embedded servers eliminate the need for external server installations. Spring Boot’s opinionated defaults and production-ready features streamline development. Additionally, it offers tools for automatic application restart, live reload, and easy dependency management, enhancing the overall development experience.

23. What is the purpose of the @SpringBootApplication annotation in a Spring Boot application?

The @SpringBootApplication annotation serves as a key component in a Spring Boot application. It combines three essential annotations: @Configuration, @EnableAutoConfiguration, and @ComponentScan.

1. @Configuration: Indicates that the class contains Spring Bean configurations.
2. @EnableAutoConfiguration: Enables automatic configuration based on classpath and dependencies.
3. @ComponentScan: Scans for Spring components, such as controllers, services, and repositories, to be managed by the Spring container.

Collectively, the @SpringBootApplication annotation simplifies the configuration and bootstrap process of a Spring Boot application, allowing for effortless setup and initialization.

Read on:- Java Tutorial to enhance your knowledge!

24. How does Spring Boot handle database connectivity and configuration?

Spring Boot simplifies database connectivity and configuration. It automatically configures database connections based on dependencies. Developers can customize settings through configuration properties in application.properties or application.yml files. Spring Boot seamlessly integrates with Spring Data JPA, providing a high-level abstraction for database operations.

It supports embedded databases for lightweight development and testing. Database health checks are available through the Spring Boot Actuator. Customization options allow for tailored configurations, and multi-database support enables working with multiple databases in a single application. Overall, Spring Boot streamlines the process of working with databases, reducing configuration and development efforts.

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

Implementing security features in a Spring Boot application can be achieved using Spring Security. Configure authentication, authorization, and role-based access control. Utilize annotations like @Secured or @PreAuthorize for method-level security. Extend WebSecurityConfigurerAdapter to customize security settings. Encrypt passwords securely using bcrypt or PBKDF2. 

Implement custom security filters for additional checks. Enable HTTPS for secure communication. Integrate with external providers like LDAP or OAuth for centralized authentication. Secure Actuator endpoints for managing sensitive information. These measures ensure robust protection against unauthorized access and maintain the integrity of Spring Boot applications.

26. How does Spring Boot support the development of RESTful APIs?

Spring Boot provides extensive support for RESTful API development. With Spring MVC, developers can define API endpoints using annotations like @RestController and map them to appropriate HTTP methods. Automatic serialization/deserialization simplifies JSON handling. 

Request mapping options handle URL patterns and content negotiation. Validation ensures data integrity. Error handling mechanisms deal with exceptions and provide meaningful error responses. 

Integration with Swagger or Springfox enables API documentation generation. Security features support authentication mechanisms. Actuator endpoints offer monitoring and management capabilities. Together, these features make Spring Boot a powerful framework for efficiently developing RESTful APIs.

27. How can you handle exceptions and errors in a Spring Boot application?

In a Spring Boot application, exceptions and errors can be handled using various approaches. Use @ExceptionHandler to handle specific exceptions, or implement a global @ControllerAdvice class for centralized exception handling. Configure custom error pages or define static HTML error pages. 

Customize HTTP error codes and error message formats. Implement logging to capture and troubleshoot exceptions. Handle validation errors using annotations or validators. Create custom exception classes for application-specific errors. These measures ensure robust error handling and provide meaningful feedback to users and clients.

28. What is the purpose of the Spring Boot DevTools, and how can they enhance development productivity?

Spring Boot DevTools aims to enhance development productivity. It offers features like automatic restart, allowing the application to restart upon code changes. Live reload detects and reloads static resource changes without a full restart. Remote debugging enables remote debugging sessions. 

DevTools provides developer-friendly defaults, such as disabling caching and showing detailed error pages. Integration with other tools, like Spring Boot Actuator, adds monitoring and configuration capabilities. These features accelerate development cycles, reduce manual effort, and improve overall productivity for developers using Spring Boot.

29. How can you deploy a Spring Boot application to a Cloud platform like Heroku or AWS?

To deploy a Spring Boot application to a Cloud platform like Heroku or AWS, follow these steps: 

• Build a production-ready JAR or WAR file.
• Create an account on the desired platform.
• Provision a server or container to host your application.
• Optionally, containerize your application if needed.
• Configure deployment settings, such as environment variables or database connections.
• Deploy the application using the platform-specific deployment methods provided.
• Set-up scaling and monitoring mechanisms to ensure the application performs optimally.
• Test and verify the functionality of the deployed application.
• Monitor and maintain the application by applying updates and patches as necessary. 

For detailed instructions and specific tools related to the deployment process, refer to the documentation provided by your chosen platform.

30. Explain the difference between Spring Boot's @Component, @Service, @Repository, and @Controller annotations. When and why would you use each of them?

The @Component, @Service, @Repository, and @Controller annotations are used in Spring Boot for component scanning and dependency injection. @Component is a generic annotation, while @Service is for business logic/service components, @Repository for data access objects, and @Controller for handling HTTP requests. 

Although they have distinct roles, they all facilitate Spring’s dependency injection. When you choose the appropriate annotation, you actively enhance clarity and structure within the codebase. It is important to note that Spring treats these annotations in a similar manner for component scanning and dependency injection, ensuring consistent functionality.