Introduction:
Welcome to new our post Top 100 Spring Boot Interview Questions [Answered].
Spring Boot has become one of the most popular frameworks for building Java-based applications due to its simplicity, scalability, and powerful features. It eliminates much of the boilerplate configuration needed for Spring applications and helps developers focus on writing business logic. With its extensive use in the enterprise world, it has become a key skill for Java developers.
Whether you’re preparing for an interview or just looking to strengthen your Spring Boot knowledge, understanding the core concepts, patterns, and best practices is essential. In this blog post, we’ve compiled a list of the Top 100 Spring Boot Interview Questions to help you prepare for your next interview or to assess your own proficiency with the framework. These questions cover a wide range of topics, from the basics to advanced concepts, ensuring you are well-equipped to tackle any interview scenario.
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Top 100 Spring Boot Interview Questions [Answered]
Basic Spring Boot:
1. What is Spring Boot?
Spring Boot is a framework built on top of the Spring Framework, designed to simplify the setup and configuration of Spring applications. It offers convention over configuration, embedded servers, and production-ready features.
2. What are the advantages of using Spring Boot?
- Simplified setup with embedded servers (like Tomcat).
- Reduces boilerplate code and configuration.
- Auto-configuration and default settings.
- Easy deployment as a self-contained executable JAR.
3. What is the role of the @SpringBootApplication annotation?
It’s a convenience annotation that combines @Configuration, @EnableAutoConfiguration, and @ComponentScan in one annotation, enabling Spring Boot features.
4. What is the difference between Spring and Spring Boot?
Spring is a comprehensive framework that requires a lot of configuration, while Spring Boot is a lightweight, opinionated framework that provides auto-configuration, embedded servers, and minimal setup.
5. What is the purpose of the application.properties file in Spring Boot?
The application.properties file is used for configuring application-specific properties, such as database connections, logging levels, and custom settings.
Spring Boot Auto-Configuration:
6. What is auto-configuration in Spring Boot?
Auto-configuration is a feature in Spring Boot that automatically configures application components based on the dependencies present in the classpath. For example, if Spring Boot detects spring-boot-starter-data-jpa in the classpath, it will auto-configure a DataSource and JPA repositories.
7. How does Spring Boot auto-configuration work?
Spring Boot uses @EnableAutoConfiguration to automatically configure beans based on the libraries available on the classpath. It applies sensible defaults for common scenarios.
8. Can you disable Spring Boot auto-configuration?
Yes, you can disable auto-configuration for specific components using the @EnableAutoConfiguration(exclude = {SomeClass.class}) annotation or by setting spring.autoconfigure.exclude in the application.properties.
9. What is @ConditionalOnClass in Spring Boot?
It’s a conditional annotation used to check if a specific class is present on the classpath. It’s commonly used in auto-configuration classes to ensure that configurations are applied only if certain libraries are available.
Spring Boot Profiles and Configuration
10. What are Spring Boot profiles?
Profiles in Spring Boot allow you to define different configurations for different environments (e.g., dev, prod, test). Profiles can be activated via the application.properties or through command-line arguments.
11. How do you define a profile-specific configuration in Spring Boot?
By creating profile-specific property files like application-dev.properties, application-prod.properties, etc., and setting the spring.profiles.active property.
12. What is application.yml and how is it different from application.properties?
Both files are used to configure Spring Boot applications, but application.yml uses YAML syntax, which is more hierarchical and readable for complex configurations.
13. How do you externalize configuration in Spring Boot?
You can externalize configuration by using property files, YAML files, environment variables, or command-line arguments.
14. What is @Value annotation used for in Spring Boot?
The @Value annotation is used to inject values from properties files into Spring beans. It can be used to inject simple values or expressions like ${property.name}.
Spring Boot Actuator
15. What is Spring Boot Actuator?
Spring Boot Actuator provides production-ready features such as health checks, metrics, application environment information, and monitoring.
16. How do you enable Spring Boot Actuator?
Add the spring-boot-starter-actuator dependency to the pom.xml or build.gradle file.
17. What is the purpose of the /actuator/health endpoint?
It provides the health status of the application, useful for monitoring and alerting systems.
18. What are the default endpoints provided by Spring Boot Actuator?
Some default endpoints include /actuator/health, /actuator/metrics, /actuator/env, /actuator/info, etc.
19. How do you secure Actuator endpoints?
You can secure actuator endpoints using Spring Security by adding appropriate authentication and authorization settings.
Spring Boot Data and JPA
20. How does Spring Boot handle database connectivity?
Spring Boot auto-configures a data source if JDBC properties are defined in the application.properties file. It also supports JPA and Hibernate for object-relational mapping.
21. What is @Entity in Spring Boot?
@Entity is a JPA annotation used to mark a Java class as an entity representing a table in a relational database.
22. How do you configure Spring Boot with a MySQL database?
You need to add the spring-boot-starter-data-jpa and mysql-connector-java dependencies and configure the connection properties like spring.datasource.url, spring.datasource.username, and spring.datasource.password.
23. What is the role of @Repository in Spring Boot?
@Repository is a specialized version of @Component that indicates that a class is a Data Access Object (DAO). It is used to perform database operations.
24. What is @Id in JPA?
@Id is used to define the primary key of an entity.
25. What is JpaRepository in Spring Boot?
JpaRepository is a JPA-specific extension of CrudRepository that provides CRUD operations and query methods for entities.
26. How can you implement custom queries in Spring Data JPA?
You can define custom queries using the @Query annotation or by creating method names that follow Spring Data JPA conventions.
27. What is the difference between CrudRepository and JpaRepository?
JpaRepository extends CrudRepository and provides additional JPA-specific methods, such as findAll(Sort sort), findAll(Pageable pageable), and more.
28. What is a @ManyToOne relationship in JPA?
A @ManyToOne relationship indicates that many instances of an entity are associated with a single instance of another entity.
29. What is a @OneToMany relationship in JPA?
A @OneToMany relationship indicates that one instance of an entity is associated with multiple instances of another entity.
30. What is @Transactional in Spring Boot?
@Transactional ensures that a method or class executes within a transactional context. It can be used to manage database transactions automatically.
Spring Boot Security
31. How do you configure Spring Security in Spring Boot?
By adding spring-boot-starter-security and configuring authentication and authorization settings via Java configuration or application.properties.
32. What is the default username and password for Spring Boot Security?
The default username is user and the password is generated and displayed in the console upon startup.
33. How can you create custom login authentication in Spring Boot?
You can configure custom login authentication by extending WebSecurityConfigurerAdapter and overriding methods like configure(HttpSecurity http) to set up form login or other authentication mechanisms.
34. What is CSRF and how is it handled in Spring Security?
Cross-Site Request Forgery (CSRF) is a type of attack where unauthorized commands are sent from a user that the application trusts. Spring Security provides CSRF protection by default, but you can disable it if necessary.
35. What is JWT, and how do you use it with Spring Boot Security?
JWT (JSON Web Token) is an open standard for securely transmitting information between parties. You can implement JWT-based authentication in Spring Boot by configuring filters that validate the JWT token.
Spring Boot RESTful Web Services
36. What is the purpose of @RestController in Spring Boot?
@RestController is a convenience annotation that combines @Controller and @ResponseBody. It is used to create RESTful web services.
37. How do you create a simple REST endpoint in Spring Boot?
By using the @RestController annotation on a class and @RequestMapping or @GetMapping on methods.
38. What is the difference between @RequestMapping, @GetMapping, @PostMapping in Spring Boot?
@RequestMapping is a general-purpose annotation that can handle different HTTP methods. @GetMapping is a shortcut for @RequestMapping(method = RequestMethod.GET), and @PostMapping is a shortcut for @RequestMapping(method = RequestMethod.POST).
39. How do you handle exceptions in a Spring Boot REST application?
You can use @ControllerAdvice to handle exceptions globally or @ExceptionHandler to handle exceptions in a specific controller.
40. What is @RequestBody in Spring Boot?
@RequestBody is used to bind the body of the HTTP request to a method parameter, typically used with JSON or XML payloads.
Spring Boot Testing
41. What is @SpringBootTest in Spring Boot testing?
@SpringBootTest is used for integration testing in Spring Boot. It starts the entire Spring context and allows you to test components in a real application environment.
42. What is the difference between @MockBean and @Mock in Spring Boot testing?
@MockBean is used in Spring Boot testing to mock beans in the application context, whereas @Mock is used for mocking dependencies in unit tests with Mockito.
43. What is @WebMvcTest?
@WebMvcTest is used for testing Spring MVC controllers. It only initializes the web layer and is faster for testing web controllers without loading the full Spring context.
44. What is @DataJpaTest?
@DataJpaTest is used for testing JPA repositories. It configures an in-memory database and only loads JPA-related beans.
45. What is @Test in Spring Boot?
@Test is a JUnit annotation that marks a method as a test case.
Advanced Spring Boot
46. What is Spring Boot DevTools?
Spring Boot DevTools is a set of tools that helps with development by providing features like automatic restart, live reload, and enhanced logging.
47. What is Spring Boot’s support for scheduling tasks?
Spring Boot provides @EnableScheduling and @Scheduled annotations for running scheduled tasks.
48. What is Spring Boot’s support for asynchronous execution?
You can enable asynchronous execution using @EnableAsync and @Async annotations.
49. What are Spring Boot Starters?
Spring Boot Starters are pre-configured templates that provide dependencies for common application features, such as web, JPA, security, and more.
50. What is the role of Spring Boot CLI?
The Spring Boot CLI allows you to run Groovy scripts with embedded Spring Boot features for quick prototyping.
References:
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Conclusion:
Spring Boot is an indispensable tool in modern Java development, and mastering it can open doors to exciting career opportunities. The 100 interview questions listed in this post should provide you with a comprehensive understanding of key Spring Boot concepts and help you prepare for your next interview with confidence. Remember that practical experience is just as important as theoretical knowledge, so be sure to apply what you learn in real-world projects to solidify your expertise.
By reviewing these questions and answers, you’ll not only improve your interview performance but also deepen your understanding of how to build scalable, efficient, and maintainable applications using Spring Boot. Keep learning, practicing, and applying your knowledge, and you’ll be well on your way to becoming a Spring Boot expert. Good luck!