Brush up on your Spring Boot skills and nail your interview! This targeted resource dives into the top 30 Spring Boot interview questions and answers, all updated for 2024. Spring Boot's prominence in the Java development world is undeniable, offering a streamlined approach to building powerful applications. Feel confident walking into your interview with a mastery of these essential questions and showcase your Spring Boot expertise.

Preparing for an interview is crucial, but landing that interview in the first place needs the right opportunities. Weekday.works can connect you to those opportunities by matching your Spring Boot expertise with companies eager to find talented engineers.

Top Spring Boot Interview Questions/Answers 

Ready to dive deep? These questions span a range of topics, ensuring you're prepared for various interview scenarios. Whether you're a seasoned developer or just getting started, this guide will solidify your Spring Boot knowledge and boost your interview confidence.

1. What is Spring Boot and How Does It Function as a Java-Based, 

Open-Source Framework?

Spring Boot is a Java-based, open-source framework designed to simplify the creation and deployment of Spring applications. It is built on top of the conventional Spring framework and inherits its robust dependency injection and configuration management capabilities. Spring Boot's primary function is to streamline the entire development process by eliminating the need for extensive XML configuration and manual setup of Spring applications. It achieves this through convention over configuration principles, providing a set of pre-configured settings that fit most projects but can be customized as needed.

2. Why is Spring Boot Considered Important in Web Development?

Spring Boot is considered crucial in web development for several reasons:

1. Rapid Development: It significantly reduces development time by automating configuration and dependency management.
2. Ease of Use: Developers can focus on writing code rather than worrying about boilerplate code and configuration.
3. Microservices Ready: It is tailored for developing microservices, an architecture style that structures an application as a collection of services that are highly maintainable and loosely coupled.
4. Production-ready Features: Spring Boot comes with built-in support for application monitoring, health checks, and externalized configuration, which are essential for deploying applications in production environments.

3. How Does Spring Boot Simplify the Development of New Spring Applications Through Auto-configuration?

Spring Boot simplifies the development of new Spring applications primarily through its auto-configuration feature. This feature automatically configures Spring and third-party libraries whenever possible, based on the context of the application. For instance, if Spring Boot detects a Spring MVC jar on your classpath, it automatically configures the necessary components to develop a web application, such as a DispatcherServlet. Auto-configuration removes the need for developers to define boilerplate configuration and allows them to focus on the unique aspects of their application.

4. What Are the Ease of Development and Productivity Benefits Provided by Spring Boot?

Spring Boot enhances ease of development and productivity by providing:

• Starter Dependencies: Simplified dependency management with "starters" which are a set of convenient dependency descriptors that you can include in your application.
• Automatic Configuration: Sensible defaults that automatically configure Spring settings based on project contents and other factors.
• Embedded Servers: Easy deployment and testing with embedded HTTP servers like Tomcat or Jetty running out of the box.
• Developer Tools: Features like live reloading and configurable options for quick application development and testing.

5. What Are the Key Components of Spring Boot?

The key components of Spring Boot include:

• Auto-configuration: This core feature attempts to automatically configure your Spring application based on the jar dependencies that you have added.
• Command Line Interface (CLI): A tool that allows you to run and test Spring Boot applications from the command line without requiring a complex IDE setup.
• Starter POMs: Pre-defined templates that aggregate common dependencies together (e.g., spring-boot-starter-web for web applications) which can be added to the project’s build configuration.
• Actuators: Provides production-ready features to help you monitor and manage your application when it’s pushed to production (e.g., metrics, health status, traffic data).

Together, these components make it significantly easier to develop, deploy, and maintain large-scale applications using Spring Framework.

6. What Role Does the @SpringBootApplication Annotation Play in Spring Boot?

The @SpringBootApplication annotation plays a pivotal role in Spring Boot as it encompasses three crucial annotations: @EnableAutoConfiguration, @ComponentScan, and @Configuration. These annotations work together to enable auto-configuration of the Spring application context, scanning for Spring components, registering them as beans, and defining configuration settings respectively. Essentially, @SpringBootApplication signals Spring Boot to start adding beans based on classpath settings, other beans, and various property settings, thereby acting as a one-stop setup for most Spring Boot applications.

7. What Are Starter Dependencies in Spring Boot and Why Are They Significant?

Starter dependencies in Spring Boot are a set of convenient dependency descriptors that help to include a group of related dependencies that are commonly used together. For example, spring-boot-starter-web brings in all the required dependencies for building web applications, including Spring MVC, Tomcat as the default embedded container, and Jackson for JSON binding. These starters simplify Maven or Gradle configuration by abstracting dependency management, ensuring that developers can get a project set up quickly with minimal fuss. They are significant because they reduce the potential for version conflicts and make it easier to upgrade dependencies across a broader suite of libraries.

8. How Can One Create a Spring Boot Application Using Spring Initializer and Boot CLI?

To create a Spring Boot application using the Spring Initializer:

1. Visit the website (start.spring.io).
2. Choose the desired project metadata (type, packaging, Java version, dependencies).
3. Click on "Generate" to download the project template.

To create an application using the Spring Boot CLI:

1. Install the Spring Boot CLI following the official documentation.
2. Use the command line to create a basic project structure. 

For example:

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This command creates a new project with dependencies for web development, JPA, and security.

9. How Is a Spring Boot Application Run Using a Main Method?

A Spring Boot application is typically run using a main method that looks like this:

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This main method serves as the entry point of the application. The SpringApplication.run() method launches the Spring Boot application by creating an appropriate ApplicationContext instance and loading beans. It also performs the auto-configuration tasks set by Spring Boot.

10. What Is the Difference Between @RestController and @Controller in Spring Boot?

In Spring Boot, @RestController and @Controller serve different roles:

• @RestController is a specialized version of the @Controller annotation that combines @Controller and @ResponseBody. This means that data returned by each method will be written directly into the response body as JSON or XML, not through view resolvers.
• @Controller is typically used when you want to return a view. It’s used in MVC web applications where @Controller classes return a template name (and model) which is then rendered by a view renderer.

11. How Does @ComponentScan Aid in Package Scanning Within Spring Boot?

@ComponentScan is used to specify the packages that the Spring Framework needs to scan for annotated components. It is automatically included in the @SpringBootApplication annotation, and it directs Spring Boot where to look for Spring components, configurations, services, and other classes that need to be registered in the application context. By default, it scans the package where the application class annotated with @SpringBootApplication is located and all its sub-packages. This is crucial for ensuring that all relevant beans are detected and auto-configured.

12. What are the Advantages of Using Spring Boot Over the Traditional Spring Framework?

Spring Boot offers several advantages over the traditional Spring Framework that streamline the development process and enhance productivity:

1. Auto-configuration: Spring Boot automatically configures your application based on the dependencies you have added, reducing the need for specifying boilerplate configuration.
2. Standalone Application: It simplifies the deployment process by allowing applications to run independently from an external web server through embedded servers like Tomcat, Jetty, or Undertow.
3. Opinionated Defaults: Provides a range of 'starter' POMs to simplify Maven configurations, offering sensible defaults that can be overridden as needed.
4. Developer Productivity: Includes features such as live reloading (Spring DevTools) and extensive metric and health check capabilities to improve the development and maintenance phases of the application lifecycle.
5. Microservices Ready: Ideal for building microservices due to its embedded server support and ease of configuration.

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13. How Can You Configure and Change the Port of the Embedded Web Server in Spring Boot?

To change the port of the embedded web server in a Spring Boot application, you can set the server.port property in the application.properties or application.yml file:

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• In application.properties:

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• In application.yml:

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This property can be overridden at runtime via command-line arguments, environment variables, or an external configuration file.

14. How Does Spring Boot Handle Dependency Management?

Spring Boot simplifies dependency management through the use of "starter" dependencies that bundle necessary libraries for specific functionalities. This ensures compatibility and reduces the risk of version conflicts. Maven or Gradle configurations are minimized as Spring Boot manages versions of all dependencies transitively.

15. How Can Specific Auto-Configuration Classes Be Disabled in Spring Boot?

Specific auto-configuration classes in Spring Boot can be disabled using the exclude attribute of the @SpringBootApplication or @EnableAutoConfiguration annotation:

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This prevents the specified auto-configuration class from being applied during the startup of the application.

16. How are @Profile Annotations Defined and Used for Environment-Specific Configurations in Spring Boot?

@Profile annotations in Spring Boot are used to specify components that should be registered only in certain profiles. Profiles represent environment-specific configurations, allowing for different configurations in development, testing, and production environments. Here’s how you might define a bean for the development profile:

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Beans defined in this configuration will only be active when the "dev" profile is active, which can be specified via the spring.profiles.active property in application.properties or as a command-line parameter.

17. How Do Actuators Contribute to Application Monitoring and Management in Spring Boot?

Actuators in Spring Boot provide built-in endpoints that allow monitoring and interacting with the application. They offer various insights, including health, metrics, info, environment properties, configuration properties, and more. Actuators are essential for observing the application’s state and behavior in production environments.

18. How Are RESTful Services Created Using @RestController in Spring Boot?

RESTful services in Spring Boot are created using the @RestController annotation, which combines @Controller and @ResponseBody. Methods in a @RestController class automatically serialize return objects into HttpResponse bodies. Here is a simple example:

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Beans defined in this configuration will only be active when the "dev" profile is active, which can be specified via the spring.profiles.active property in application.properties or as a command-line parameter.

19. How Do Actuators Contribute to Application Monitoring and Management in Spring Boot?

Actuators in Spring Boot provide built-in endpoints that allow monitoring and interaction with the application. They offer various insights, including health, metrics, info, environment properties, configuration properties, and more. Actuators are essential for observing the application’s state and behavior in production environments.

20. How Are RESTful Services Created Using @RestController in Spring Boot?

RESTful services in Spring Boot are created using the @RestController annotation, which combines @Controller and @ResponseBody. Methods in a @RestController class automatically serialize return objects into HttpResponse bodies. Here is a simple example:

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This configuration sets up Swagger to document your API and provides a UI to access the API documentation typically available at /swagger-ui.html.

21. What are the Differences Between RequestMapping and GetMapping in Spring Boot?

@RequestMapping and @GetMapping are annotations in Spring Boot used to map web requests to Spring Controller methods. @RequestMapping is a more general annotation that can handle requests of all HTTP methods unless specified otherwise. It can be configured to handle GET, POST, PUT, DELETE, and other request methods through its method attribute. For example:

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@GetMapping, on the other hand, is a specialized version of @RequestMapping that is a shortcut for a request method of GET. It simplifies the annotation by removing the need to specify the method:

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@GetMapping is preferred for clarity and brevity when dealing with GET requests.

22. Why is Spring Boot Suitable for Microservices Architecture?

Spring Boot is particularly well-suited for microservices architecture for several reasons:

• Independence: It supports the development of stand-alone applications that can be deployed independently.
• Embedded Servers: Spring Boot applications can run with an embedded server like Tomcat, Jetty, or Undertow, simplifying service deployment and scalability.
• Environment Adaptability: It offers features like externalized configuration and profiles that help manage different configurations for different environments easily (dev, test, prod).
• Service Discovery and Registration: Integration with Spring Cloud provides service discovery and registration capabilities that are necessary for microservices architectures.

23. What Features Support Microservices Development in Spring Boot?

Key features supporting microservices development in Spring Boot include:

• Embedded Servers: Allows microservices to run independently without needing an external application server, simplifying deployment and scaling.
• Actuator Integration: Provides built-in endpoints for monitoring and managing microservices which are vital for checking the health, metrics, and environment of services in production.
• Auto-Configuration: Simplifies application setup and reduces boilerplate code by automatically configuring Spring and third-party libraries based on the classes detected on the classpath.

24. How Does Spring Boot Compare to Other Java Frameworks?

Compared to other frameworks and libraries:

• JAX-RS is a specification for building RESTful web services in Java, used by frameworks like Jersey and RESTEasy. Unlike Spring Boot, JAX-RS focuses only on web services and does not provide the comprehensive infrastructure support (like embedded servers or extensive configuration management) that Spring Boot does.
• Hibernate is an ORM (Object-Relational Mapping) framework for handling database operations. Hibernate focuses on data persistence and is often used within Spring Boot applications for ORM capabilities. Spring Boot itself offers a higher-level integration with Hibernate through Spring Data JPA, simplifying repository pattern implementations and data access layers.

25. What are the Benefits of Bootstrapping with Spring Boot Compared to Using the Traditional Spring Framework?

Bootstrapping with Spring Boot offers several benefits over the traditional Spring Framework:

• Reduced Configuration: Spring Boot reduces the need for explicit bean and configuration setup through its auto-configuration features, allowing developers to start new projects quickly and with fewer configurations.
• Faster Development: Built-in tools and operations, such as embedded servers and developer tools, enhance developer productivity by enabling rapid application testing and development.
• Simplified Dependency Management: The use of starter POMs simplifies Maven or Gradle configurations by bundling commonly used dependencies together, ensuring version compatibility.
• Production-readiness: Spring Boot provides production-ready features such as monitoring, metrics, and health checks out of the box, which are crucial for deploying robust applications.

26. What is the default port of Tomcat in Spring Boot?

The default port of the embedded Tomcat server in Spring Boot is 8080. We can change the default port by setting the server.port property in your application’s application.properties file.

27. Can we disable the default web server in the Spring Boot application?

Yes, we can disable the default web server in the Spring Boot application. To do this, we need to set the server.port property to “-1” in the application’s application.properties file.

28. Explain @RestController annotation in Spring Boot.

@RestController annotation is like a shortcut to building RESTful services. It combines two annotations:

• @Controller: Marks the class as a request handler in the Spring MVC framework.
• @ResponseBody: Tells Spring to convert method return values (objects, data) directly into HTTP responses instead of rendering views.

It enables us to Define endpoints for different HTTP methods (GET, POST, PUT, DELETE), return data in various formats (JSON, XML, etc.), and map the request parameters to method arguments.

29. What are the differences between @SpringBootApplication and @EnableAutoConfiguration annotation?

30. What are the Spring Boot Annotations?

• @SpringBootApplication: A configuration class that defines one or more @Bean methods and initiates auto-configuration and component scanning is indicated by the annotation.
• @EnableAutoConfiguration: Using the jar dependencies you have provided, the @EnableAutoConfiguration annotation instructs Spring Boot to "guess" how you want to configure Spring.
• @ConditionalOnMissingClass: The Class conditions are these comments' home. Depending on the existence or absence of particular classes, a configuration can be included using the @ConditionalOnClass and @ConditionalOnMissingClass annotations.
• @Conditional: A class evaluating the specific condition can be made for circumstances that are even more complicated.

Conclusion     

Conquer your Spring Boot interview with confidence! This comprehensive guide, updated for 2024, tackles the top Spring Boot interview questions and equips you with expert answers. Remember that finding the right position is just as critical as acing your interviews. Weekday.works can help you land interviews at companies looking for your specific expertise, making your job search as efficient as your code.