Top 25 Spring Boot Interview Questions and Answers

 1. What is Spring Boot?

Spring Boot is an extension of the Spring framework that simplifies the process of creating stand-alone, production-grade Spring-based applications. It offers a range of features such as auto-configuration, embedded servers, and production-ready features, which minimize the need for configuration and boilerplate code.

2. What are the main features of Spring Boot?

Key features include:

• Auto-Configuration: Automatically configures Spring applications based on the dependencies present.
• Standalone: Spring Boot applications can run independently as standalone Java applications.
• Embedded Servers: Includes embedded Tomcat, Jetty, or Undertow servers to simplify deployment.
• Production Ready: Includes built-in features like metrics, health checks, and externalized configuration.

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

Spring is a comprehensive framework for enterprise Java development, while Spring Boot is a project that simplifies and accelerates Spring application development by providing default configurations and setup out of the box.

4. What is a Spring Boot Starter?

Starters are a set of convenient dependency descriptors you can include in your application. For example, spring-boot-starter-web brings in all the dependencies needed for a web application, including Tomcat and Spring MVC.

5. Explain the role of the @SpringBootApplication annotation.

@SpringBootApplication is a convenience annotation that combines @Configuration, @EnableAutoConfiguration, and @ComponentScan. It sets up Spring Boot's configuration, enables auto-configuration, and scans for Spring components in the specified package.

6. How do you create a Spring Boot application?

You can create a Spring Boot application by:

• Using Spring Initializr (https://start.spring.io) to bootstrap a new project.
• Adding the required dependencies.
• Writing the main application class annotated with @SpringBootApplication.
• Running the application with SpringApplication.run(YourApplication.class, args).

7. What is application.properties or application.yml?

These files are used for externalized configuration in Spring Boot applications. They allow you to define properties and settings such as server port, database configurations, and custom application settings.

8. How can you externalize configuration in Spring Boot?

Configuration can be externalized using:

• application.properties or application.yml files.
• Environment variables.
• Command-line arguments.
• Spring Cloud Config server for distributed configuration.

9. What is Spring Boot Actuator?

Spring Boot Actuator provides production-ready features such as monitoring and managing your application through endpoints like /actuator/health, /actuator/metrics, and /actuator/info. It helps with application insights and management.

10. What is a Spring Boot dependency management?

Spring Boot dependency management simplifies the handling of dependencies by providing a set of pre-configured dependencies and versions through its spring-boot-dependencies BOM (Bill Of Materials). This ensures compatibility and reduces conflicts.

11. What is @RestController used for?

@RestController is a specialized version of @Controller that is used to create RESTful web services. It combines @Controller and @ResponseBody, which means it automatically serializes the response body into JSON or XML.

12. How can you handle exceptions in Spring Boot?

Exceptions can be handled using:

• @ControllerAdvice and @ExceptionHandler to define global exception handlers.
• Custom error pages and error attributes by defining a @Controller with @ExceptionHandler methods.
• Spring Boot's built-in error handling with BasicErrorController.

13. What is Spring Boot's auto-configuration?

Auto-configuration is a feature of Spring Boot that automatically configures your application based on the dependencies and settings present in the classpath. It reduces the need for manual configuration by guessing and setting up the required beans.

14. What is a Spring Boot CLI?

The Spring Boot Command Line Interface (CLI) is a tool that allows you to run and test Spring Boot applications from the command line using Groovy scripts. It provides a way to develop applications quickly without needing to write traditional Java classes.

15.How do you define a Spring Boot profile?

Profiles in Spring Boot are defined using the spring.profiles.active property in application.properties or application.yml. Profiles can be used to create different configurations for different environments (e.g., development, testing, production).

16. How does Spring Boot handle data persistence?

Spring Boot handles data persistence through Spring Data JPA, which simplifies database interactions by providing a repository abstraction. It also supports other persistence frameworks like MyBatis, JDBC, and MongoDB.

17. What is the purpose of the @Component annotation?

@Component is a generic stereotype annotation used to mark a class as a Spring-managed component. It is a generic form of annotations such as @Service, @Repository, and @Controller, which are used for more specific purposes.

18. How can you integrate Spring Boot with a database?

You can integrate Spring Boot with a database by:

• Adding the relevant database dependency (e.g., H2, MySQL, PostgreSQL) to your project.
• Configuring the database connection details in application.properties or application.yml.
• Defining @Entity classes and repositories to handle data operations.

19. What is Spring Boot DevTools?

Spring Boot DevTools provides additional development-time features such as automatic restarts, live reloads, and enhanced debugging. It helps to improve the development experience by reducing the need to manually restart the application.

20. How do you handle logging in Spring Boot?

Spring Boot uses Commons Logging for internal logging but defaults to Logback for logging. You can configure logging levels and appenders in application.properties or application.yml.

21. What is a @ConfigurationProperties annotation used for?

@ConfigurationProperties is used to bind external configuration properties to a Java object. It allows grouping and validation of properties defined in application.properties or application.yml into a strongly-typed configuration class.

22. How does Spring Boot's embedded server work?

Spring Boot's embedded server is bundled with the application as a dependency (e.g., Tomcat, Jetty, or Undertow). When the application starts, the embedded server is initialized and starts listening for HTTP requests, eliminating the need for external server configuration.

23. What is Spring Boot's approach to security?

Spring Boot provides security through Spring Security. By default, it sets up basic security configurations, including user authentication and authorization. Custom security settings can be configured by extending WebSecurityConfigurerAdapter and defining custom security rules.

24. What are the best practices for using Spring Boot?

Best practices include:

• Using @Configuration and @Component for bean management.
• Externalizing configuration properties.
• Keeping application code modular and organized.
• Leveraging Spring Boot's auto-configuration to reduce manual configuration.
• Writing integration tests and using Spring Boot Test features.

25. What are some common Spring Boot annotations?

Common annotations include:

• @SpringBootApplication
• @RestController
• @RequestMapping
• @Autowired
• @Component
• @Service
• @Repository
• @Configuration
• @Value