Spring Interview Questions

Core Spring Concepts

1. What is Spring Framework?

Answer: Spring is a powerful open-source framework for building Java applications. It provides a comprehensive infrastructure for developing enterprise-level applications with features like dependency injection, aspect-oriented programming, and transaction management.

2. Explain Dependency Injection (DI).

Answer: DI is a core principle of Spring. It involves injecting dependencies (objects that a class needs) into the class instead of the class creating them itself. This promotes loose coupling and makes the application more maintainable and testable.

3. What are the different types of Dependency Injection?

Answer:

Constructor Injection: Dependencies are provided through the class constructor.

Setter Injection: Dependencies are injected through setter methods.

4. What is ApplicationContext in Spring?

Answer: ApplicationContext is the heart of the Spring framework. It’s an interface that provides access to the beans defined in the Spring configuration. It loads bean definitions and manages the lifecycle of beans.

5. Explain the concept of AOP (Aspect-Oriented Programming) in Spring.

Answer: AOP allows you to modularize cross-cutting concerns (like logging, security, and transaction management) that affect multiple parts of the application. This improves code reusability and maintainability.

6. What are the key components of AOP?

Answer:

Aspect: A module that encapsulates cross-cutting concerns.

Join Point: A point in the execution of the program (e.g., method execution, exception handling).

Pointcut: An expression that defines which join points to intercept.

Advice: The action to be taken at a particular join point (e.g., before, after, around).

7. What is Spring Boot?

Answer: Spring Boot simplifies Spring development by providing an opinionated approach to creating stand-alone, production-grade Spring applications with minimal configuration.

8. How does Spring Boot simplify development?

Answer:

Autoconfiguration: Automatically configures Spring based on dependencies on the classpath.

Embedded Servers: Easily embed servers like Tomcat or Jetty within the application.

Opinionated Starter Projects: Provides pre-configured starter dependencies for common use cases.

9. What is Spring MVC?

Answer: Spring MVC is a powerful framework for building web applications on top of the Spring platform. It provides features like request mapping, controller handling, view resolution, and data binding.

10. Explain the role of DispatcherServlet in Spring MVC.

Answer: DispatcherServlet is the front controller in Spring MVC. It receives all incoming requests and dispatches them to the appropriate handler (controller).

Spring Data

11. What is Spring Data JPA?

Answer: Spring Data JPA simplifies JPA development by providing a higher-level abstraction. It significantly reduces the amount of boilerplate code needed to interact with the database.

12. Explain the concept of repositories in Spring Data JPA.

Answer: Repositories are interfaces that define data access methods for entities. Spring Data JPA automatically generates implementations for these interfaces based on the method names.

13. What are some common repository methods in Spring Data JPA?

Answer:

findAll()

findById()

save()

delete()

findBy<PropertyName>(<Value>)

14. What is Spring Data JDBC?

Answer: Spring Data JDBC provides a simpler way to interact with relational databases using JDBC. It offers a higher-level abstraction over JDBC templates.

15. How does Spring Data JDBC simplify database interactions?

Answer:

Provides a more concise and expressive way to write database queries.

Offers built-in support for common database operations.

Reduces the amount of boilerplate code required.

Spring Security

16. What is Spring Security?

Answer: Spring Security is a framework for securing Spring-based applications. It provides features like authentication, authorization, and data protection.

17. Explain the core concepts of authentication and authorization.

Answer:

Authentication: The process of verifying the identity of a user.

Authorization: The process of determining whether a user has the necessary permissions to access a particular resource.

18. How does Spring Security handle authentication?

Answer:

Supports various authentication mechanisms like username/password, LDAP, OAuth 2.0.

Provides built-in support for user details services.

19. How does Spring Security handle authorization?

Answer:

Uses access control lists (ACLs) or role-based access control (RBAC) to determine access permissions.

Provides mechanisms like method-level security and expression-based access control.

20. What is JWT (JSON Web Token)?

Answer: JWT is a compact and self-contained way to securely transmit information between parties as JSON objects. It’s often used for authentication and authorization in modern applications.

Spring Testing

21. What are some common testing frameworks used with Spring?

Answer:

JUnit

Mockito

Spring Test

AssertJ

22. Explain the role of @SpringBootTest annotation.

Answer: This annotation loads the entire Spring application context for integration tests.

23. How can you mock dependencies in Spring tests?

Answer:

Use the @MockBean annotation to create mock objects for beans.

Use Mockito to define the behavior of mock objects.

Spring Cloud

24. What is Spring Cloud?

Answer: Spring Cloud provides tools for building distributed systems on top of the Spring platform. It offers solutions for service discovery, configuration management, and message routing.

25. What is service discovery in Spring Cloud?

Answer: Service discovery allows services to dynamically locate and communicate with each other in a distributed environment. Spring Cloud provides implementations of service registries like Eureka and Consul.

26. What is API Gateway in Spring Cloud?

Answer: API Gateway acts as a single entry point for all clients to access microservices. It handles routing, security, and load balancing.

27. What is Spring Cloud Config?

Answer: Spring Cloud Config provides a centralized way to manage application configurations. It allows you to store and retrieve configuration properties from a central server.

Spring Transactions

28. What is transaction management in Spring?

Answer: Transaction management ensures that a series of database operations are executed as a single unit. If any operation fails, the entire transaction is rolled back.

29. What are the different types of transaction propagation?

Answer:

REQUIRED: If a transaction is already in progress, join it; otherwise, start a new one.

REQUIRES_NEW: Always start a new transaction.

NEVER: Execute only within an existing transaction; otherwise, throw an exception.

30. Explain the role of @Transactional annotation.

Answer: This annotation is used to define transaction boundaries for methods.

Spring Batch

31. What is Spring Batch?

Answer: Spring Batch is a framework for processing large volumes of data in a reliable and efficient manner. It provides features like job scheduling, step execution, and resource management.

32. What are the key components of a Spring Batch job?

Answer:

Job: Represents the overall processing unit.

Step: A single unit of work within a job.

ItemReader: Reads data from a source.

ItemProcessor: Transforms the data.

ItemWriter: Writes the processed data to a destination.

Spring Integration

33. What is Spring Integration?

Answer: Spring Integration provides a framework for building enterprise integration solutions. It allows you to connect different applications and systems using various messaging protocols.

34. Explain the concept of message channels and endpoints in Spring Integration.

Answer:

Message Channels: Transport messages between endpoints.

Endpoints: Handle messages, such as sending them to a service or receiving them from a queue.

Spring WebFlux

35. What is Spring WebFlux?

Answer: Spring WebFlux is a reactive framework for building web applications on top of the Spring platform. It’s built on Project Reactor and supports asynchronous, non-blocking operations.

36. What are the benefits of using Spring WebFlux?

Answer:

Improved performance and scalability.

Better handling of high concurrency.

Reduced resource consumption.

Spring Data Redis

37. What is Spring Data Redis?

Answer: Spring Data Redis simplifies the interaction with Redis. It provides a higher-level abstraction over Redis commands.

38. What are some common Redis data structures supported by Spring Data Redis?

Answer:

Strings

Hashes

Lists

Sets

Sorted Sets

Spring Cloud Stream

39. What is Spring Cloud Stream?

Answer: Spring Cloud Stream provides a framework for building message-driven microservices. It allows you to easily connect to message brokers like Kafka and RabbitMQ.

Spring Cloud Kubernetes

40. What is Spring Cloud Kubernetes?

Answer: Spring Cloud Kubernetes provides integration with Kubernetes, a popular container orchestration platform. It simplifies the deployment and management of Spring applications on Kubernetes.

Advanced Topics

41. Explain the concept of aspect-oriented programming (AOP) in Spring.

Answer: AOP allows you to modularize cross-cutting concerns (like logging, security, and transaction management) that affect multiple parts of the application. This improves code reusability and maintainability.

42. What are the different types of advice in AOP?

Answer:

Before advice: Executed before the method is invoked.

After advice: Executed after the method is invoked, regardless of the outcome.

AfterReturning advice: Executed after the method is invoked successfully.

AfterThrowing advice: Executed if the method throws an exception.

Around advice: Executes both before and after the method is invoked.

43. What are the different types of bean scopes in Spring?

Answer:

Singleton: Only one instance of the bean is created per Spring ApplicationContext.

Prototype: A new instance of the bean is created each time it’s requested.

Request: A new instance of the bean is created for each HTTP request.

Session: A new instance of the bean is created for each HTTP session. 

44. Explain the concept of circular dependencies in Spring.

Answer: A circular dependency occurs when two or more beans have a dependency on each other. This can lead to errors during bean creation.

45. How can you resolve circular dependencies in Spring?

Answer:

Constructor Injection: Avoid circular dependencies by using constructor injection.

@Lazy annotation: Make one of the beans lazy-loaded.

46. What is the difference between an interface and an abstract class?

Answer:

Interface: Can only contain abstract methods and constant fields. Can be implemented by any class, regardless of its hierarchy.

Abstract Class: Can contain both abstract and concrete methods. Can only be inherited by other classes.

47. What is the difference between HashMap and HashSet?

Answer:

HashMap: Stores data in key-value pairs. Allows duplicate values but not duplicate keys.

HashSet: Stores only unique elements. Does not maintain any order.

48. What is the difference between an array and a list?

Answer:

Array: A fixed-size collection of elements of the same data type.

List: A dynamic-size collection of elements that can be accessed by index.

49. What is the difference between an interface and a functional interface?

Answer:

Interface: Can contain any number of methods.

Functional Interface: Can contain only one abstract method.

50. Explain the concept of lambda expressions in Java.

Answer: Lambda expressions provide a concise way to represent anonymous functions. They are used to implement functional interfaces.