Spring Basics for Interview

Most Asked Java & Spring Boot Interview Questions at Info Edge (with Detailed Answers)

---

1. What is Spring Boot, and how does it differ from the Spring Framework?

Answer: Spring Boot is an extension of the Spring Framework that simplifies the process of creating stand-alone, production-grade Spring applications. It reduces boilerplate code and configuration by providing:

• Auto-Configuration: Automatically configures your application based on dependencies.

• Embedded Servers: Uses Tomcat, Jetty, or Undertow embedded in the app.

• Starter POMs: Provides dependencies grouped by functionality.

• Production-Ready Features: Metrics, health checks, externalized config via Spring Boot Actuator.

Difference from Spring Framework: Spring requires manual configuration of dependencies, servers, and setups, while Spring Boot minimizes this effort with sensible defaults.

---

2. Explain Dependency Injection and Inversion of Control.

Answer:

• Inversion of Control (IoC): It’s a design principle where the control of object creation and dependency management is transferred from the application code to the Spring container.

• Dependency Injection (DI): It is a pattern used to implement IoC. Objects are provided their dependencies instead of creating them manually.

Types in Spring:

• Constructor Injection

• Setter Injection

• Field Injection (not recommended for testing)

Example:

@Component
public class Car {
    private final Engine engine;
    @Autowired
    public Car(Engine engine) {
        this.engine = engine;
    }
}

---

3. What are the different scopes of Spring Beans?

Answer: Spring defines several bean scopes:

• Singleton (default): One instance per Spring container.

• Prototype: New instance each time it's requested.

• Request: One instance per HTTP request (web only).

• Session: One instance per HTTP session.

• Application: One instance per ServletContext.

• Websocket: One instance per WebSocket session.

Usage:

@Bean
@Scope("prototype")
public MyBean myBean() {
    return new MyBean();
}

---

4. How does Spring Boot manage application properties and profiles?

Answer:

• Uses application.properties or application.yml to externalize configuration.

• Profiles like dev, test, prod can be defined using:

spring.profiles.active=dev

• Profile-specific files: application-dev.properties

• Can use @Profile("dev") to restrict beans to certain environments.

---

5. What is the purpose of the @SpringBootApplication annotation?

Answer: It is a convenience annotation that combines:

• @Configuration: Marks the class as a source of bean definitions.

• @EnableAutoConfiguration: Tells Spring Boot to start auto-configuration.

• @ComponentScan: Scans for components in the package and its sub-packages.

Example:

@SpringBootApplication
public class MyApp {
    public static void main(String[] args) {
        SpringApplication.run(MyApp.class, args);
    }
}

---

6. How do you handle exceptions in Spring Boot applications?

Answer: Use:

• @ControllerAdvice: Global exception handler.

• @ExceptionHandler: Handles specific exceptions.

Example:

@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<String> handleNotFound(ResourceNotFoundException ex) {
        return new ResponseEntity<>(ex.getMessage(), HttpStatus.NOT_FOUND);
    }
}

---

7. What is the difference between @Controller and @RestController?

Answer:

• @Controller: Used to define web controllers; requires @ResponseBody to return data.

• @RestController: Combines @Controller and @ResponseBody, suitable for REST APIs.

Example:

@RestController
public class MyController {
    @GetMapping("/hello")
    public String sayHello() {
        return "Hello, World!";
    }
}

---

8. Explain the use of Spring Boot Actuator.

Answer: Spring Boot Actuator provides endpoints to monitor and manage your app:

• /actuator/health

• /actuator/metrics

• /actuator/env

Add to pom.xml:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

Enable endpoints in application.properties:

management.endpoints.web.exposure.include=*

---

9. How do you implement pagination and sorting in Spring Data JPA?

Answer: Use PagingAndSortingRepository or JpaRepository:

Page<User> findByAge(int age, Pageable pageable);

Usage:

PageRequest pageRequest = PageRequest.of(0, 10, Sort.by("name"));
Page<User> users = userRepository.findByAge(25, pageRequest);

---

10. What are the differences between CrudRepository and JpaRepository?

Answer:

• CrudRepository: Basic CRUD operations.

• JpaRepository: Extends CrudRepository, adds:

  • Batch operations

  • Pagination and Sorting support

  • flush(), saveAndFlush(), deleteInBatch() methods

Use JpaRepository when: You need full JPA functionality with additional features beyond basic CRUD.

---