✅ 1️⃣ Core Spring Framework — Interview Questions

1️⃣ What is Spring Framework?

Spring is a lightweight Java framework used to build loosely coupled, testable, and maintainable applications using IoC, DI, and AOP.

2️⃣ What is Inversion of Control (IoC)?

IoC means Spring Framework controls object creation, not the developer.

Without IoC:


Service s = new Service();

With IoC:
Spring creates and injects it automatically.

3️⃣ What is Dependency Injection (DI)?

DI provides required dependencies from outside instead of creating internally.

Example:


@Service
public class OrderService {

    private final PaymentService paymentService;

    public OrderService(PaymentService paymentService) {
        this.paymentService = paymentService;
    }
}

4️⃣ What is a Spring Bean?

A bean is an object managed by Spring Container.

5️⃣ Bean Scopes?

singleton (default)
prototype
request
session

Example:


@Component
@Scope("prototype")
class TestBean {}

6️⃣ What is @Component, @Service, @Repository, @Controller?

They are stereotype annotations:

@Component – generic bean
@Service – business logic
@Repository – database + exception translation
@Controller – MVC controller

7️⃣ What is @Autowired?

Used to inject dependencies automatically.

8️⃣ Difference between @Bean and @Component?

@Component → class level auto scanning
@Bean → method level manual bean creation

9️⃣ What is AOP in Spring?

Aspect Oriented Programming — handles cross-cutting concerns like logging, security.

🔟 What is @Transactional?

Handles transactions automatically.


@Transactional
public void transfer() {}

1️⃣1️⃣ What is Spring MVC?

Framework for building web apps using MVC architecture.

1️⃣2️⃣ What is DispatcherServlet?

Front Controller in Spring MVC.

1️⃣3️⃣ What is ViewResolver?

Maps view names to actual pages.

1️⃣4️⃣ What are Profiles?

Used to define environments (dev/test/prod)

1️⃣5️⃣ What is Bean Lifecycle?

Bean creation → Dependency Injection → Initialization → Destruction

1️⃣6️⃣ What is @Lazy?

Delays bean creation until first use.


@Lazy
@Component
class Demo{}

1️⃣7️⃣ What is @Primary?

Used when multiple beans exist for same type.

1️⃣8️⃣ What is @Qualifier?

Used to choose specific bean.


@Autowired
@Qualifier("emailService")
Service service;

1️⃣9️⃣ What is ApplicationContext?

It is Spring’s IoC container.

2️⃣0️⃣ What is BeanFactory?

Basic container (ApplicationContext is advanced BeanFactory)

🚀 2️⃣ Spring Boot — Interview Questions

2️⃣1️⃣ What is Spring Boot?

Spring Boot simplifies Spring by providing:
✔ Auto Configuration
✔ Embedded Server
✔ Starter dependencies

2️⃣2️⃣ Difference — Spring vs Spring Boot?

Spring	Spring Boot
Manual config	Auto Config
Needs server	Has embedded Tomcat
Many dependencies	Starters simplify

2️⃣3️⃣ What is @SpringBootApplication?

Combination of:

@Configuration
@EnableAutoConfiguration
@ComponentScan

2️⃣4️⃣ How to create REST API?


@RestController
@RequestMapping("/api")
public class HelloController {
    @GetMapping("/hello")
    public String hello() {
        return "Hello Spring Boot";
    }
}

2️⃣5️⃣ What are Starters?

Ready dependency packs like:

spring-boot-starter-web
spring-boot-starter-data-jpa
spring-boot-starter-test

2️⃣6️⃣ application.properties vs application.yml?

Both used for configuration.

2️⃣7️⃣ What is Spring Boot Actuator?

Provides health & monitoring endpoints.


management.endpoints.web.exposure.include=*

2️⃣8️⃣ What is Auto Configuration?

Spring Boot configures beans automatically based on dependencies.

2️⃣9️⃣ How to Change Server Port?


server.port=8081

3️⃣0️⃣ What is @RestController vs @Controller?

Controller	RestController
returns view	returns JSON
uses @ResponseBody manually	built-in

🗄 3️⃣ Spring Boot + Database / JPA

3️⃣1️⃣ How to configure DB?


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

3️⃣2️⃣ What is JPA Repository?


public interface UserRepo extends JpaRepository<User, Long> {}

3️⃣3️⃣ Entity Example


@Entity
class User {
 @Id
 @GeneratedValue
 Long id;
 String name;
}

3️⃣4️⃣ What is Hibernate?

ORM Framework used by JPA.

3️⃣5️⃣ What is @Entity?

Marks class as database table.

3️⃣6️⃣ What is @Id & @GeneratedValue?

Primary key + auto increment.

3️⃣7️⃣ Difference between save() and saveAll()?

save() — single record
saveAll() — multiple records

🔐 4️⃣ Spring Security

3️⃣8️⃣ What is Spring Security?

Framework for authentication + authorization.

3️⃣9️⃣ How to secure endpoint?


http.authorizeRequests()
 .anyRequest().authenticated()
 .and()
 .httpBasic();

4️⃣0️⃣ What is OAuth2?

Authorization framework.

🧪 5️⃣ Spring Boot Testing

4️⃣1️⃣ How to Unit Test?


@SpringBootTest
class TestApp {}

4️⃣2️⃣ MockMVC Example


@Autowired
MockMvc mockMvc;

4️⃣3️⃣ Test REST API


mockMvc.perform(get("/api/hello"))
       .andExpect(status().isOk());

⚙ 6️⃣ Advanced Spring Questions

4️⃣4️⃣ What is Microservices?

Small independent services communicating via REST.

4️⃣5️⃣ What is REST?

Representational State Transfer — Web API standard.

4️⃣6️⃣ What is Feign Client?

Used for calling other microservices.

4️⃣7️⃣ What is Eureka?

Service registry.

4️⃣8️⃣ What is Circuit Breaker?

Prevents failures in distributed systems.

4️⃣9️⃣ What is @Value?

Reads values from properties.


@Value("${app.name}")
String name;

5️⃣0️⃣ Difference between Monolithic & Microservice?

Monolithic	Microservices
Single app	Multiple small services
Hard to scale	Easy to scale
Single failure kills app	Independent failure handling

Spring & Spring Boot — Top 50 Interview Questions & Answers (With Simple Code)