Spring Boot Interview Questions and Answers

This question assesses your understanding of the fundamental concept of Spring Boot, including its primary purpose and the advantages it provides over traditional Spring frameworks.  

Sample Answer:    

Spring Boot is a framework designed to simplify the development of Spring-based Applications by providing default configurations and embedded servers. It eliminates the need for extensive boilerplate code and configuration, enabling faster and more efficient Application Development.

This question evaluates your knowledge of the critical dependencies needed to work with Spring Boot, reflecting your understanding of how to set up and manage a Spring Boot project.  

Sample Answer:    

Essential dependencies for Spring Boot typically include `spring-boot-starter`, which provides core features, `spring-boot-starter-web` for building web applications, `spring-boot-starter-data-jpa` for database interaction, and `spring-boot-starter-test` for testing. These dependencies simplify the integration of various functionalities, allowing developers to focus on writing business logic rather than configuring multiple libraries. 

This question checks your ability to articulate the specific benefits of using Spring Boot, particularly in comparison to traditional Spring frameworks.  

Sample Answer:    

Spring Boot offers several advantages, including auto-configuration, which reduces the need for manual setup, embedded servers like Tomcat or Jetty that simplify deployment, and a wide array of starters that streamline Dependency Management. Additionally, it supports production-ready features like health checks and monitoring, making it ideal for creating microservices and modern web applications. 

This question gauges your knowledge of Thymeleaf, a templating engine, and how it integrates with Spring Boot for building dynamic web pages.  

Sample Answer:    

Thymeleaf is a Java-based templating engine used to create dynamic web pages in Spring Boot applications. It allows developers to seamlessly integrate HTML with server-side data, making it easier to build and maintain web applications. Thymeleaf is designed to work well with Spring Model, View, and Controller (MVC), providing features like template inheritance, fragments, and internationalisation support. 

This question examines your understanding of Swagger and its use in documenting and testing RESTful APIs within a Spring Boot application.  

Sample Answer:    

Swagger is an open-source tool used for documenting and testing RESTful Application Programming Interfaces (APIs) in Spring Boot applications. By integrating Swagger with Spring Boot, developers can automatically generate interactive API documentation, making it easier to understand, test, and maintain the APIs. Swagger also provides a user-friendly interface where clients can interact with the API endpoints without needing to write custom code. 

This question evaluates your knowledge of Spring Initializr and its role in simplifying the setup of new Spring Boot projects.  

Sample Answer:    

Spring Initializr is a web-based tool that helps developers quickly bootstrap a Spring Boot project by generating a pre-configured project structure with the necessary dependencies. It allows you to select the required dependencies, Java version, and build tool (Maven or Gradle) and then download a ready-to-use project. This tool significantly reduces the time needed to set up a new Spring Boot application, allowing Java Developers to focus on writing code rather than configuring the project. 

This question examines your understanding of Spring Boot DevTools and how it aids in the development process.  

Sample Answer:    

Spring Boot DevTools is a set of tools that enhances the development experience by providing features like automatic restarts, live reload, and configurations for faster feedback. It allows developers to make changes in the code and immediately see the results without needing to restart the entire application manually. This significantly speeds up the development process and improves productivity. 

This question evaluates your understanding of Spring Boot Starters and their role in simplifying dependency management. 

Sample Answer:    

Spring Boot Starters are a set of convenient dependency descriptors that you can include in your project to quickly add a group of related dependencies. Some common starters include `spring-boot-starter-web` for web applications, `spring-boot-starter-data-jpa` for database access, and `spring-boot-starter-test` for testing. These starters simplify the process of adding necessary dependencies, allowing developers to quickly configure and start working on their applications. 

This question evaluates your understanding of the fundamental differences between the Spring framework and Spring Boot.  

Sample Answer:    

Spring is a comprehensive framework for building Java applications, providing features like dependency injection, aspect-oriented programming, and transaction management. Spring Boot, on the other hand, is an extension of Spring that simplifies the process of creating stand-alone, production-ready applications with minimal configuration. While Spring requires extensive setup, Spring Boot provides auto-configuration, embedded servers, and starter dependencies to reduce boilerplate and accelerate development. 

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This question tests your understanding of Spring Boot Actuator and its role in monitoring and managing Spring Boot applications. 

Sample Answer:    

Spring Boot Actuator is a sub-framework within Spring Boot that provides various management and monitoring capabilities. It offers endpoints that give insights into the application’s health, metrics, environment, and more. This tool is particularly useful for gaining real-time information about a running application, which is crucial for maintaining the performance and reliability of production systems. 

This question assesses your practical understanding of how to use Thymeleaf within a Spring Boot application to render dynamic web content.  

Sample Answer:    

"Thymeleaf can be utilised in a Spring Boot application by including the `spring-boot-starter-thymeleaf` dependency. It allows developers to create Hypertext Markup Language (HTML) templates that interact with Spring MVC controllers. Thymeleaf’s syntax enables data binding, loops, conditionals, and template fragments, making it a powerful tool for rendering dynamic content based on the application's data and logic."  

This question tests your knowledge of Spring Boot Profiles, which are used to manage environment-specific configurations within an application.  

Sample Answer:    

Profiles in Spring Boot are a way to separate configuration and behaviour based on different environments, such as development, testing, and production. Profiles allow developers to define environment-specific beans and properties, which are activated based on the active profile set at runtime. This ensures that the application behaves appropriately depending on the environment it is deployed in. 

This question checks your knowledge of how to control and customise the auto-configuration behaviour in a Spring Boot Application. 

Sample Answer:    

A specific auto-configuration in Spring Boot can be disabled by using the `@EnableAutoConfiguration(exclude = {ClassName.class})` annotation on the application class or by adding `spring.autoconfigure.exclude=ClassName` in the application’s properties or YAML file. This allows developers to prevent certain configurations from being applied, giving them greater control over the application's setup. 

This question checks your knowledge of writing integration tests within the Spring Boot framework to ensure that different parts of the application work together as expected.  

Sample Answer:    

Integration tests in Spring Boot can be written using the `@SpringBootTest` annotation, which loads the full application context. You can combine this with testing frameworks like Open Source Java Unit (JUnit) or Test Next Generation (TestNG). Additionally, you can use `@MockBean` to mock dependencies and `@TestRestTemplate` to test RESTful endpoints. Spring Boot simplifies integration testing by automatically configuring the application context, which allows for thorough testing of the application’s behaviour in a real-world scenario.

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This question checks your understanding of the different ways Spring Boot can manage external configurations, which is essential for making applications environment-independent. 

Sample Answer:    

Spring Boot allows for external configuration from several sources, including properties files (`application.properties` or `application.yml`), environment variables, command-line arguments, Java system properties, and Java Naming and Directory Interface API (JNDI). This flexibility enables developers to manage configurations in a centralised manner, allowing for easy adjustments across different environments without altering the application code. 

This question evaluates your understanding of configuration management in Spring Boot and the trade-offs between using properties files and YAML.  

Sample Answer:    

Whether to use properties or Yet Another Markup Language (YAML) in Spring Boot largely depends on the project's needs. Properties files are simple and straightforward but can become cumbersome with complex configurations. YAML, on the other hand, offers a more structured and readable format, making it better suited for complex configurations. However, properties files might be preferred for their simplicity and wider support across tools. Ultimately, the choice depends on the specific requirements of the project and team preference. 

This question assesses your understanding of the differences between Spring Data JPA and Hibernate, two widely used tools in the Java ecosystem.  

Sample Answer:    

Spring Data JPA is a part of the Spring framework that simplifies data access using Java Persistence API (JPA), offering a repository abstraction layer. Hibernate is an implementation of JPA that provides the actual Object-Relational Mapping (ORM) functionalities. While Hibernate is focused on ORM, Spring Data JPA provides additional abstractions and conveniences, like custom queries, making it easier to interact with the database. 

This question tests your understanding of the concept of relaxed binding in Spring Boot and its significance in configuration. 

Sample Answer:    

Relaxed binding in Spring Boot refers to the framework's ability to map configuration properties in a flexible manner, allowing for variations in naming conventions. For example, `my.property-name`, `my.propertyName`, and `MY_PROPERTY_NAME` would all be mapped to the same property. This feature makes it easier to work with different configuration styles and ensures that properties are correctly bound to their respective fields in the application. 

This question evaluates your understanding of the annotations required to create and configure an interceptor in a Spring Boot application.  

Sample Answer:    

To create an interceptor in Spring Boot, you typically use the `@Component` annotation to register the interceptor as a Spring bean and `@Configuration` to define a configuration class that implements `WebMvcConfigurer`. Within this configuration class, you override the `addInterceptors` method to add your custom interceptor. Additionally, `@Override` may be used on methods within the interceptor class, such as `preHandle`, `postHandle`, and `afterCompletion`

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This question assesses your understanding of how to create and register a custom auto-configuration class in Spring Boot, which is useful for extending the framework’s capabilities.  

Sample Answer:    

To register a custom auto-configuration in Spring Boot, you first need to create a configuration class annotated with `@Configuration` and include the necessary beans. Then, use the `@AutoConfigureAfter` or `@AutoConfigureBefore` annotations to specify the order of application. Finally, list the custom configuration class in the `META-INF/spring.factories` file under the `org.springframework.boot.autoconfigure.EnableAutoConfiguration` key. This process allows your custom configuration to be automatically applied under specific conditions. 

This question examines your understanding of deploying Spring Boot applications in different formats.  

Sample Answer:    

Spring Boot web applications can be packaged and deployed as both Java ARchive (JAR) and Web Application Resource or Web application ARchive (WAR) files. By default, Spring Boot creates a self-contained JAR file with an embedded server, which can be run independently. To deploy as a WAR file, you need to extend `SpringBootServletInitializer` and override the `configure` method in the application class. The WAR file can then be deployed to a traditional application server like Tomcat or Jetty. 

This question tests your practical knowledge of creating a Spring Boot application using the IDE-supported Spring Starter Project Wizard.  

Sample Answer:    

To create a Spring Boot application using the Spring Starter Project Wizard, open your Integrated Development Environment (IDE), e.g., IntelliJ IDEA, Eclipse, and select the option to create a new project. Choose Spring Starter Project, then configure the project metadata, such as group, artefact, and dependencies. The wizard simplifies the setup process by generating a pre-configured Spring Boot project based on your selections, allowing you to start coding immediately.  

This question assesses your ability to set up and create a Spring Boot application using Maven, a popular build tool.  

Sample Answer:    

To create a Spring Boot Application using Maven, you can either manually create a `pom.xml` file with the necessary Spring Boot dependencies or use Spring Initializr to generate the project structure. Alternatively, you can create a Maven project in your IDE, add the Spring Boot starter dependencies to the `pom.xml`, and start building your application. Maven handles the dependency management and build process, ensuring that all required libraries are available and up to date.