1. What is the difference between Monolithic and Microservices architecture?

Answer:

FeatureMonolithicMicroservices

StructureSingle applicationMultiple independent services

ScalabilityHard to scaleEasy to scale

DeploymentEntire app redeployedIndependent services deployed

PerformanceCan be slowFaster due to service isolation

2. How do you handle database transactions in Spring Boot?

Answer:
Spring Boot uses @Transactional for transaction management.

Example:

@Service public class BankService { @Transactional public void transferMoney(Long senderId, Long receiverId, double amount) { debitAccount(senderId, amount); creditAccount(receiverId, amount); } }

3. How does Spring Boot handle concurrency and multithreading?

Answer:
Spring Boot supports asynchronous processing using @Async.

Example:

@Async public CompletableFuture<String> processTask() { return CompletableFuture.completedFuture("Task Completed"); }

4. What is WebFlux in Spring Boot?

Answer:
Spring WebFlux is a reactive programming model for handling non-blocking requests.

5. What is the difference between synchronous and asynchronous calls?

Answer:

FeatureSynchronousAsynchronous

ExecutionBlocks executionDoesn’t block execution

ExampleREST API callsWebSockets, Kafka

6. How do you integrate Redis caching in Spring Boot?

Answer:
Use @Cacheable with Redis.

Example:

@Cacheable(value = "users", key = "#id") public User getUserById(Long id) { return userRepository.findById(id).orElse(null); }

7. What are Design Patterns used in Java Full Stack?

Answer:

• Singleton – Ensures one instance

• Factory Pattern – Creates objects dynamically

• Observer Pattern – Event-driven programming

• MVC – Separates UI, business logic, and data

8. How does Hibernate manage session and entity lifecycle?

Answer:
Hibernate follows four states:

• Transient (Not in DB)

• Persistent (Managed by Hibernate)

• Detached (Not managed but exists in DB)

• Removed (Deleted from DB)

9. What is the difference between OAuth and JWT authentication?

Answer:

FeatureOAuthJWT

UsageAuthorizationAuthentication

Data FormatTokens with scopesJSON token

10. What is Circuit Breaker Pattern in Microservices?

Answer:
Circuit Breaker prevents system failure by stopping calls to failing services using Resilience4J.

Example:

@CircuitBreaker(name = "serviceA", fallbackMethod = "fallbackMethod") public String callServiceA() { return restTemplate.getForObject("http://service-a/api", String.class); }

11. How does Kubernetes manage Java Full Stack applications?

Answer:
Kubernetes orchestrates containerized applications, ensuring scalability and resilience.

12. How do you deploy a Spring Boot application in Docker?

Answer:

1. Create a Dockerfile:

FROM openjdk:11 COPY target/app.jar app.jar CMD ["java", "-jar", "app.jar"]

1. Build and run the container:

docker build -t myapp . docker run -p 8080:8080 myapp

13. What is API Gateway, and how does it work?

Answer:
API Gateway (like Zuul or Spring Cloud Gateway) acts as a single entry point to route requests in microservices.

14. What is the difference between WebSockets and Server-Sent Events (SSE)?

Answer:

FeatureWebSocketsSSE

DirectionBi-directionalOne-way (server to client)

Use CaseChat applicationsReal-time updates

15. How does Spring Security handle Role-Based Access Control (RBAC)?

Answer:
Use @PreAuthorize for method-level security.

Example:

@PreAuthorize("hasRole('ADMIN')") public void adminOnlyTask() { }

16. How do you improve the performance of a Java Full Stack application?

Answer:

• Enable caching (Redis, Ehcache)

• Use asynchronous processing

• Optimize database queries

• Implement lazy loading in Hibernate

17. What is the difference between GraphQL and REST?

Answer:

FeatureGraphQLREST

Data FetchingFetches only required dataFetches full response

PerformanceFasterCan be slow

18. How do you implement file uploads in Spring Boot?

Answer:
Use MultipartFile.

Example:

@PostMapping("/upload") public String uploadFile(@RequestParam("file") MultipartFile file) { String fileName = file.getOriginalFilename(); return "Uploaded: " + fileName; }

19. How do you use RabbitMQ in Java Full Stack?

Answer:
RabbitMQ is a message broker used for asynchronous processing.

Example:

@RabbitListener(queues = "queueName") public void processMessage(String message) { System.out.println("Received: " + message); }

20. How do you handle large-scale database migrations?

Answer:
Use Flyway or Liquibase for managing database versioning.

21. What is the difference between Full Stack and MEAN/MERN stack?

Answer:

StackTechnologies

Java Full StackJava, Spring Boot, Angular/React, MySQL

MEANMongoDB, Express, Angular, Node.js

MERNMongoDB, Express, React, Node.js

22. How do you handle CORS issues in Spring Boot?

Answer:
Enable CORS globally:

@Bean public WebMvcConfigurer corsConfigurer() { return new WebMvcConfigurer() { @Override public void addCorsMappings(CorsRegistry registry) { registry.addMapping("/**").allowedOrigins("*"); } }; }

23. What is Load Balancing, and how is it achieved in Java Full Stack?

Answer:
Load balancing distributes traffic among multiple servers using NGINX, HAProxy, or AWS ELB.

24. What are Idempotent REST APIs, and why are they important?

Answer:
Idempotent APIs return the same result no matter how many times they are called.

Example:

• GET /user/1 – Always returns the same user

• PUT /user/1 – Always updates the user, without creating duplicates

25. How do you optimize React for better performance?

Answer:

• Use React.memo() for memoization

• Optimize useEffect() dependencies

• Enable lazy loading for components

• Use Redux Toolkit for efficient state management