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Preparing for a Full Stack Java Developer interview? Whether you’re a fresher, mid-level, or senior developer, this guide covers the top 20 questions and answers that interviewers commonly ask in 2025.

✅ Full Stack Java Developer Interview Questions & Answers

1. What is a Full Stack Java Developer?

A Full Stack Java Developer is proficient in both front-end and back-end technologies, especially with Java on the server side. They can develop entire web applications and are familiar with databases, APIs, DevOps, and UI technologies.

2. Technologies commonly used by Full Stack Java Developers

• Front-End: HTML, CSS, JavaScript, React, Angular, Vue.js
• Back-End: Java, Spring, Spring Boot, Hibernate, JPA
• Databases: MySQL, PostgreSQL, MongoDB, Oracle
• Build Tools: Maven, Gradle
• Version Control: Git
• CI/CD: Jenkins, Docker, Kubernetes

3. What is the MVC architecture?

MVC (Model-View-Controller) divides an application:

• Model: Business logic and data.
• View: UI.
• Controller: Handles user input and updates model/view.

4. What is Spring Boot and why is it used?

Spring Boot simplifies Spring-based application development by:

• Reducing boilerplate config
• Providing embedded servers
• Supporting microservices architecture
• Easy integration with tools like Maven and Docker

5. How to create a RESTful web service in Spring Boot?

java

@RestController
@RequestMapping("/api/users")
public class UserController {

    @GetMapping
    public List<User> getAllUsers() {
        return userService.findAll();
    }

    @PostMapping
    public User createUser(@RequestBody User user) {
        return userService.save(user);
    }
}

6. What is Hibernate and how does it work?

Hibernate is an ORM that maps Java classes to database tables. It manages database operations using:

• Annotations or XML
• Session API for CRUD operations

7. How is transaction management handled in Spring?

Using @Transactional to ensure atomic operations.

java

@Transactional
public void registerUser(User user) {
    userRepository.save(user);
    emailService.sendWelcomeEmail(user);
}

8. Purpose of application.properties in Spring Boot

Used for configuration like:

properties

spring.datasource.url=jdbc:postgresql://localhost:5432/mydb
server.port=8080
logging.level.org.springframework=DEBUG

9. What is Dependency Injection (DI) in Spring?

DI injects dependencies into classes rather than creating them internally.

java

@Service
public class UserService {
    private final UserRepository repo;

    @Autowired
    public UserService(UserRepository repo) {
        this.repo = repo;
    }
}

10. Difference between @Component, @Service, @Repository, and @Controller

AnnotationPurpose@ComponentGeneric Spring bean@ServiceService layer logic@RepositoryDAO layer with DB operations@ControllerMVC Controller, handles web requests

11. How to secure a Spring Boot app?

Using Spring Security:

java

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

12. What is Docker and how is it used in Java development?

Docker packages apps into containers for consistent deployment.

Example Dockerfile:

Dockerfile

FROM openjdk:17
COPY target/app.jar app.jar
ENTRYPOINT ["java", "-jar", "/app.jar"]

13. How to integrate React with Spring Boot?

1. Build React app with npm run build
2. Place static files in src/main/resources/static/
3. Use React for front-end, Spring Boot REST for back-end

14. What are WebSockets?

WebSockets provide real-time communication between client and server.

• Used for live chats, notifications, etc.
• In Spring: @EnableWebSocket + custom WebSocketHandler

15. How to handle async processing in Spring?

Using @Async and Executor:

java

@Async
public void sendEmail(String to) {
    // non-blocking operation
}

16. What are Microservices?

Architecture style where applications are split into small, independent services.

• Spring Boot + Spring Cloud used for implementation

17. How is configuration managed in microservices?

Using Spring Cloud Config Server:

• Stores config in Git
• Centralized configuration for all services

18. What is an API Gateway?

It routes requests to appropriate microservices and handles:

• Auth, rate limiting, logging
• Tools: Spring Cloud Gateway, Zuul

19. What is CI/CD?

• CI (Continuous Integration): Automate build/test
• CD (Continuous Deployment): Automate deployment
• Tools: Jenkins, GitHub Actions, GitLab CI

20. How do you ensure performance and scalability?

• Use caching (Redis)
• Load balancing
• Connection pooling
• Optimize DB queries
• Asynchronous processing