<h3>1. What is Spring Boot and how is it different from Spring Framework?</h3><p>Spring Boot is an extension of the Spring Framework that simplifies the setup, configuration, and deployment of Spring applications. It provides auto-configuration, embedded servers, and production-ready features with minimal boilerplate code.</p><h3><span style="font-size: 19px">2. What are the advantages of using Spring Boot?</span></h3><ul><li style="background-color: transparent">Auto-configuration</li><li style="background-color: transparent">Embedded servers (Tomcat, Jetty, Undertow)</li><li style="background-color: transparent">Production-ready features (metrics, health checks)</li><li style="background-color: transparent">No code generation or XML configuration required</li><li style="background-color: transparent">Rapid development and easy deployment</li></ul><h3><span style="font-size: 19px">3. What is “starter” in Spring Boot?</span></h3><p><span style="font-size: 19px">​A starter is a set of convenient dependency descriptors you can include in your application. For example, <code>spring-boot-starter-web</code> includes all dependencies for building a web application.</span></p><h3><span style="font-size: 19px">4. What is auto-configuration in Spring Boot?</span></h3><p><span style="font-size: 19px">​Auto-configuration automatically configures your Spring application based on the dependencies present in the classpath. It reduces the need for manual configuration.</span></p><h3><span style="font-size: 19px">5. How do you create a Spring Boot application?<br></span></h3><ul><li style="background-color: transparent">Use <a href="https://start.spring.io/" target="_blank" rel="noopener noreferrer">Spring Initializr</a></li><li style="background-color: transparent">Add <code>@SpringBootApplication</code> annotation to your main class</li><li style="background-color: transparent">Run the main method</li></ul><h3>6. What is the purpose of the <code>@SpringBootApplication</code> annotation?​<br></h3><p>​It is a combination of <code>@Configuration</code>, <code>@EnableAutoConfiguration</code>, and <code>@ComponentScan</code>. It marks the main class of a Spring Boot application.</p><h3>7. How do you externalize configuration in Spring Boot?​</h3><p>​Using <code>application.properties</code> or <code>application.yml</code> files, environment variables, or command-line arguments.</p><h3>8. How do you define a custom configuration property?​<br></h3><p>Create a POJO with fields, annotate with <code>@ConfigurationProperties</code>, and enable it with <code>@EnableConfigurationProperties</code> or <code>@Component</code>.</p><h3>9. What is the difference between <code>@Component</code>, <code>@Service</code>, <code>@Repository</code>, and <code>@Controller</code>?​<br></h3><p>All are stereotypes for Spring beans, but they indicate different roles:</p><ul><li style="background-color: transparent"><code>@Component</code>: Generic bean</li><li style="background-color: transparent"><code>@Service</code>: Service layer</li><li style="background-color: transparent"><code>@Repository</code>: Data access layer, adds exception translation</li><li style="background-color: transparent"><code>@Controller</code>: Web controller</li></ul><h3><strong class="">10. How do you handle exceptions in Spring Boot REST APIs?</strong></h3><ul><li style="background-color: transparent">Use <code>@ControllerAdvice</code> and <code>@ExceptionHandler</code></li><li style="background-color: transparent">Return custom error responses</li></ul><h3><strong class="">11. What is Spring Boot Actuator?</strong></h3><p>A set of production-ready features to help you monitor and manage your application (health, metrics, info, environment, etc.).</p><p><strong class="">12. How do you enable and use Actuator endpoints?</strong></p><p>Add <code>spring-boot-starter-actuator</code> dependency and configure endpoints in <code>application.properties</code>.</p><h3><strong class="">13. How do you connect Spring Boot to a database?</strong></h3><p>Add the appropriate starter (e.g., <code>spring-boot-starter-data-jpa</code>), configure datasource properties, and use Spring Data repositories.</p><h3><strong class="">14. What is Spring Data JPA?</strong></h3><p>A part of Spring Data that makes it easy to implement JPA-based repositories with minimal boilerplate.</p><h3><strong class="">15. How do you implement pagination and sorting in Spring Boot?</strong></h3><p>Use <code>PagingAndSortingRepository</code> or pass <code>Pageable</code> and <code>Sort</code> parameters to repository methods.</p><h3><strong class="">16. How do you secure a Spring Boot application?</strong></h3><p>Add <code>spring-boot-starter-security</code>, configure security settings, and use annotations like <code>@PreAuthorize</code>.</p><h3><strong class="">17. What is the use of <code>@RestController</code>?</strong></h3><p>It is a combination of <code>@Controller</code> and <code>@ResponseBody</code>, used to create RESTful web services.</p><h3><strong class="">18. How do you create a custom endpoint in Spring Boot Actuator?</strong></h3><p>Implement <code>Endpoint</code> or use <code>@Endpoint</code> annotation.</p><h3><strong class="">19. How do you profile environments in Spring Boot?</strong></h3><p>Use <code>@Profile</code> annotation and separate property files like <code>application-dev.properties</code>.</p><h3><strong class="">20. How do you run code at application startup?</strong></h3><p>Implement <code>CommandLineRunner</code> or <code>ApplicationRunner</code> interface.</p>

Core Spring Boot Interview Questions

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