Top 25+ Spring Boot Interview Questions and Answers – Devduniya

Spring Boot is a popular framework for developing Java applications and microservices. It provides a convenient way to configure and bootstrap Spring-based applications and offers a wide range of features and tools for building robust, production-ready systems. As a result, Spring Boot is a highly sought-after skill for Java developers. In this blog, we will cover some of the most commonly asked interview questions and answers for Spring Boot to help you prepare for your next job interview. From understanding the basics of the framework to diving into advanced concepts, this guide will give you a solid understanding of what to expect and how to showcase your expertise in Spring Boot.

Q1. What is Spring Boot?

Answer: Spring Boot is a framework for building standalone, production-ready Spring applications. It provides a convenient way to create and configure Spring-powered applications, with sensible defaults and minimal configuration.

Q2. What are the advantages of using Spring Boot?

Answer: Spring Boot provides several advantages, including:

• Auto-configuration of Spring-powered applications
• Production-ready features, such as metrics and health checks
• Embeddable web servers, allowing for easy deployment
• Simplified configuration and setup, with sensible defaults

Q3. How does Spring Boot differ from Spring Framework?

Answer: Spring Boot is built on top of the Spring Framework, and provides a simplified way to create and configure Spring-powered applications. It also includes additional features for production-ready applications, such as metrics and health checks.

Q4. What is the role of the @SpringBootApplication annotation?

Answer: The @SpringBootApplication annotation is used to configure and enable Spring Boot features in a Spring application. It is a convenience annotation that combines several other commonly used Spring annotations, including @Configuration, @EnableAutoConfiguration, and @ComponentScan.

Q5. What is the difference between @Component, @Service, and @Repository annotations?

Answer: @Component is a generic stereotype annotation for any Spring-managed component.
@Service and @Repository are specialized versions of @Component, used to indicate that a class serves as a service (i.e., it contains business logic) or a repository (i.e., it interacts with a database), respectively.

Q6. How can you enable JPA in a Spring Boot application?

Answer: To enable JPA in a Spring Boot application, you should include the Spring Data JPA starter dependency in your project’s pom.xml file.

org.springframework.boot
spring-boot-starter-data-jpa

Q7. How can you enable Hibernate in a Spring Boot application?

Answer: Hibernate is enabled by default when you include the Spring Data JPA starter dependency in your project’s pom.xml file.

Q8. What is the difference between a Bean and a Component in Spring?

Answer: A Bean is a Java object that is managed by Spring’s IoC container. A component is a stereotype annotation for a Spring Bean, which allows for easy discovery and wiring of beans in a Spring application.

Q9. How can you define a property in a Spring Boot application?

Answer: Properties in a Spring Boot application can be defined in a variety of ways, including:

• In an application.properties or application.yml file
• In command-line arguments passed to the application
• As environment variables

Q10. What is the difference between a RestController and a Controller in Spring?

Answer: A RestController is a specialized version of a Controller, used to handle HTTP requests. It is used to handle RESTful web services, and returns an HTTP response to the client.

Q11. What is the difference between @Autowired and @Inject annotations?

Answer: Both @Autowired and @Inject are used to request a dependency injection in Spring. However, @Autowired is a Spring-specific annotation, while @Inject is a standard annotation defined by JSR-330.

Q12. What is the difference between @Value and @Autowired?

Answer: @Value is used to specify a default value for a bean property, while @Autowired is used to request dependency injection for a bean property.

Q14. How can you secure a Spring Boot application?

Answer: Spring Boot provides several options for securing an application, including:

• Basic Authentication: Uses a simple username and password for authentication
• Form-based Authentication: Uses a login form for authentication
• OAuth 2.0: Uses a token-based authentication mechanism
• JWT: Uses a JSON Web Token for authentication

Q15. How can you implement exception handling in a Spring Boot application?

Answer: Spring Boot provides a @ControllerAdvice annotation that can be used to handle exceptions globally across the application. You can also use the @ExceptionHandler annotation to handle specific exceptions in individual controllers. Additionally, you can use the @RestControllerAdvice annotation to handle exceptions in RESTful controllers and return appropriate HTTP status codes and error messages.

@RestControllerAdvice
public class GlobalExceptionHandler {
@ExceptionHandler(value = Exception.class)
public ResponseEntity handleException(Exception ex) {
ErrorResponse error = new ErrorResponse();
error.setErrorCode(HttpStatus.INTERNAL_SERVER_ERROR.value());
error.setMessage(ex.getMessage());
return new ResponseEntity<>(error, HttpStatus.INTERNAL_SERVER_ERROR);
}
}

This example shows a GlobalExceptionHandler class that uses the @RestControllerAdvice annotation to handle exceptions globally and return an HTTP status code of 500 (Internal Server Error) and a custom error message.

Q16. How can you configure a datasource in Spring Boot?

Answer: Spring Boot provides several ways to configure a datasource, including:

• Using application.properties or application.yml file to define properties such as the JDBC URL, username, and password.
• Using the Spring Boot CLI to configure the datasource by passing in command-line arguments
• Using JNDI to look up the datasource from a JNDI provider
• Using the DataSourceBuilder class to programmatically build a DataSource bean.

spring.datasource.url=jdbc:mysql://localhost:3306/mydb
spring.datasource.username=root
spring.datasource.password=password

This example shows how to configure a MySQL datasource in an application.properties file. The JDBC URL, username, and password are specified for the datasource.

Q17. How can you create a RESTful web service in Spring Boot?

Answer: You can create a RESTful web service in Spring Boot by using the @RestController annotation on a class. This annotation is used to indicate that the class is a RESTful web service controller, and methods within the class are used to handle HTTP requests. Additionally, you can use Spring Boot’s built-in support for Jackson to automatically convert Java objects to JSON, and vice versa.

@RestController
@RequestMapping("/api/users")
public class UserController {
@GetMapping
public List getAllUsers() {
// code to return a list of users
}
@PostMapping
public User createUser(@RequestBody User user) {
// code to create a new user
}
@PutMapping("/{id}")
public User updateUser(@PathVariable Long id, @RequestBody User user) {
// code to update an existing user
}
@DeleteMapping("/{id}")
public void deleteUser(@PathVariable Long id) {
// code to delete a user
}
}

This example shows a UserController class that is annotated with the @RestController annotation and has methods that handle HTTP GET, POST, PUT, and DELETE requests.

Q18. How can you enable caching in a Spring Boot application?

Answer: Spring Boot provides built-in support for caching using the Spring Framework’s caching abstraction. You can enable caching by adding the Spring Boot Starter Cache dependency to your project’s pom.xml file and using the @EnableCaching annotation on a configuration class. You can also use the @Cacheable, @CacheEvict and @CachePut annotations to enable caching on specific methods.

@Configuration
@EnableCaching
public class CachingConfig {
@Bean
public CacheManager cacheManager() {
    SimpleCacheManager cacheManager = new SimpleCacheManager();
    cacheManager.setCaches(Arrays.asList(new ConcurrentMapCache("users")));
    return cacheManager;
}
}
@Service
public class UserService {
@Cacheable("users")
public User getUser(Long id) {
// code to retrieve a user from the database
}
}

Q19. How can you use the Actuator in a Spring Boot application?

Answer: Spring Boot Actuator is a sub-project of Spring Boot that provides several production-ready features, such as monitoring and management of the application. To use Actuator in your Spring Boot application, you need to include the Spring Boot Actuator starter dependency in your pom.xml file and configure the endpoints in the application.properties or application.yml file. Once this is done, you can access various metrics and health information about the application using the provided endpoints.

management.endpoints.web.exposure.include=*

This example shows how to enable all Actuator endpoints in the application.properties file.

Q20. How can you use the Spring Security in a Spring Boot application?

Answer: Spring Security is a powerful and highly customizable authentication and access-control framework. To use Spring Security in a Spring Boot application, you need to include the Spring Boot Security starter dependency in your pom.xml file and add the @EnableWebSecurity annotation to a configuration class. You can then use the HttpSecurity object to configure various security settings such as authentication and authorization.

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
@Autowired
private UserDetailsService userDetailsService;

@Override
protected void configure(HttpSecurity http) throws Exception {
    http
        .authorizeRequests()
            .antMatchers("/").permitAll()
            .anyRequest().authenticated()
            .and()
        .formLogin()
            .loginPage("/login")
            .permitAll()
            .and()
        .logout()
            .permitAll();
}

@Autowired
public void configureGlobal(AuthenticationManagerBuilder auth) throws Exception {
    auth.userDetailsService(userDetailsService).passwordEncoder(passwordEncoder());
}

@Bean
public PasswordEncoder passwordEncoder() {
    return new BCryptPasswordEncoder();
}
}

This example shows a SecurityConfig class that extends the WebSecurityConfigurerAdapter and overrides the configure method to set up form-based authentication and authorization.

Q21. How can you use Logging in a Spring Boot application?

Answer: Spring Boot provides support for logging using the logback framework by default. You can configure logging in a Spring Boot application by adding a logback.xml or logback-spring.xml file in the classpath. You can also use application.properties or application.yml file to configure the logging level and other settings.

logging.level.org.springframework=DEBUG
logging.file=logs/application.log

This example shows how to configure the logging level for the org.springframework package to DEBUG and specify the location of the log file.

Q22. How can you use the Spring Profiles in a Spring Boot application?

Answer: Spring Profiles allow you to configure different properties and beans for different environments. You can use Spring Profiles in Spring Boot by using the Spring Boot specific profile-related properties in application.properties or application.yml file, such as spring.profiles.active.

spring.profiles.active=dev

Q23. How can you use the Spring Data in a Spring Boot application?

Answer: Spring Data is a set of libraries that provide a simple way to interact with different types of data stores, such as relational databases, NoSQL databases, and cloud-based data stores. To use Spring Data in a Spring Boot application, you need to include the Spring Boot Starter Data dependency in your pom.xml file and create repositories that extend Spring Data’s CrudRepository or JpaRepository interfaces.

@Repository
public interface UserRepository extends JpaRepository {
User findByUsername(String username);
}

This example shows a UserRepository interface that extends the JpaRepository interface and defines a custom findByUsername method.

Q24. How can you use the Spring WebFlux in a Spring Boot application?

Answer: Spring WebFlux is a non-blocking, reactive-streams-based programming model for building web applications using Spring Framework. To use Spring WebFlux in a Spring Boot application, you need to include the Spring Boot Starter WebFlux dependency in your pom.xml file and use the @EnableWebFlux annotation on a configuration class. Additionally, you can use the RouterFunctions and RouterFunction classes to define routing and handling of HTTP requests.

@Configuration
@EnableWebFlux
public class WebFluxConfig {
@Bean
public RouterFunction<ServerResponse> route(UserHandler handler) {
    return RouterFunctions
            .route(GET("/users"), handler::getAllUsers)
            .andRoute(POST("/users"), handler::createUser);
}
}

This example shows a WebFluxConfig class that uses the RouterFunctions class to define routing for HTTP GET and POST requests to the “/users” endpoint and maps them to methods in the UserHandler class.

Q25. How can you use the Spring Scheduling in a Spring Boot application?

Answer: Spring Scheduling allows you to schedule the execution of tasks at a specific time or at a specific interval. To use Spring Scheduling in a Spring Boot application, you need to enable scheduling by using the @EnableScheduling annotation on a configuration class. You can then use the @Scheduled annotation on a method to schedule its execution.

@Configuration
@EnableScheduling
public class SchedulingConfig {
@Scheduled(fixedRate = 5000)
public void scheduleTask() {
    // code to execute the task
}
}

This example shows a SchedulingConfig class that enables scheduling and defines a method scheduleTask that is executed every 5 seconds using the fixedRate attribute of the @Scheduled annotation.

Q26. How can you use the Spring Batch in a Spring Boot application?

Answer: Spring Batch is a lightweight, comprehensive batch framework designed to handle the bulk of batch processing jobs. To use Spring Batch in a Spring Boot application, you need to include the Spring Boot Starter Batch dependency in your pom.xml file, and create a Job with one or more Steps and configure them accordingly.

@Configuration
@EnableBatchProcessing
public class BatchConfig {
@Autowired
public JobBuilderFactory jobBuilderFactory;
@Autowired
public StepBuilderFactory stepBuilderFactory;

@Bean
public Job importUserJob(Step step1) {
    return jobBuilderFactory.get("importUserJob")
            .incrementer(new RunIdIncrementer())
            .flow(step1)
            .end()
            .build();
}

@Bean
public Step step1() {
    return stepBuilderFactory.get("step1")
            .<User, User> chunk(10)
            .reader(reader())
            .processor(processor())
            .writer(writer())
            .build();
}
// other beans for reader, processor and writer
}

This example shows a BatchConfig class that enables batch processing and defines a Job that has one step, and that step reads, processes and writes data in chunks of 10 records.

Q27. How can you use the Spring Security OAuth2 in a Spring Boot application?

Answer: Spring Security OAuth2 is a powerful and highly customizable authentication and access-control framework for securing OAuth2-enabled applications. To use Spring Security OAuth2 in a Spring Boot application, you need to include the Spring Boot Starter Security and Spring Boot Starter OAuth2 Client dependencies in your pom.xml file, and configure the OAuth2 client properties in the application.properties or application.yml file. You can also create an OAuth2 client configuration class and use the @EnableOAuth2Client annotation to enable the OAuth2 client support.

@Configuration
@EnableOAuth2Client
public class OAuth2ClientConfig extends WebSecurityConfigurerAdapter {
@Autowired
private OAuth2ClientProperties oAuth2ClientProperties;
@Bean
public OAuth2AuthorizedClientService authorizedClientService() {
    return new InMemoryOAuth2AuthorizedClientService(clientRegistrationRepository());
}

@Bean
public ClientRegistrationRepository clientRegistrationRepository() {
    return new InMemoryClientRegistrationRepository(clientRegistration());
}

private ClientRegistration clientRegistration() {
    return CommonOAuth2Provider.GOOGLE.getBuilder(oAuth2ClientProperties.getClientId())
            .clientId(oAuth2ClientProperties.getClientId())
            .clientSecret(oAuth2ClientProperties.getClientSecret())
            .build();
}
}

This example shows an OAuth2ClientConfig class that enables OAuth2 client support and configures a Google OAuth2 client using properties defined in the application.properties or application.yml

Conclusion:

Overall, Spring Boot is a powerful and versatile framework for building Java applications and microservices. By understanding the key concepts and being able to confidently answer common interview questions, you’ll be well-prepared to excel in a job interview and demonstrate your expertise in Spring Boot. With a combination of knowledge, hands-on experience, and practice, you can take your skills to the next level and be on your way to a successful career in Java development.

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