SpringBoot

🔹 1. What is Spring Boot 3.x and how is it different from 2.x?

✅ Answer:

• Spring Boot 3.x is built on Spring Framework 6 and requires Java 17+.

• It supports Jakarta EE 10 (javax → jakarta).

• Embraces native image support via GraalVM.

• Full support for Observability via Micrometer and Actuator enhancements.

• Removed deprecated classes/APIs from 2.x.

🔹 2. How to enable auto-configuration in Spring Boot?

✅ Answer:

Spring Boot uses @SpringBootApplication which includes @EnableAutoConfiguration.

@SpringBootApplication

public class MyApplication {

public static void main(String[] args) {

SpringApplication.run(MyApplication.class, args);

}

}

You can exclude a configuration:

@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})

🔹 3. How do you handle exceptions globally in Spring Boot?

✅ Answer:

Use @ControllerAdvice and @ExceptionHandler.

@ControllerAdvice

public class GlobalExceptionHandler {

@ExceptionHandler(ResourceNotFoundException.class)

public ResponseEntity<String> handleNotFound(ResourceNotFoundException ex) {

return ResponseEntity.status(HttpStatus.NOT_FOUND).body(ex.getMessage());

}

}

🔹 4. How does Spring Boot support Observability (Micrometer + Actuator)?

✅ Answer:

Spring Boot Actuator 3.x provides:

• Tracing with OpenTelemetry.

• Micrometer metrics (CPU, memory, requests).

• /actuator/metrics, /actuator/health, /actuator/prometheus.

Enable in application.yml:

management:

endpoints:

web:

exposure:

include: "*"

tracing:

enabled: true

metrics:

export:

prometheus:

enabled: true

🔹 5. What is the difference between @Component, @Service, and @Repository?

✅ Answer:

All are stereotype annotations for Spring-managed beans.

Annotation

Purpose

@Component

Generic component

@Service

Business logic or service layer

@Repository

DAO layer, auto exception translation

🔹 6. How do you write a REST Controller in Spring Boot?

✅ Example:

@RestController

@RequestMapping("/api/users")

public class UserController {

@GetMapping("/{id}")

public ResponseEntity<User> getUser(@PathVariable Long id) {

return ResponseEntity.ok(new User(id, "Lokesh"));

}

}

🔹 7. How to connect Spring Boot with a database (JPA + H2)?

✅ Example:

application.yml

spring:

datasource:

url: jdbc:h2:mem:testdb

h2:

console:

enabled: true

jpa:

hibernate:

ddl-auto: update

Entity:

@Entity

public class Product {

@Id @GeneratedValue

private Long id;

private String name;

}

Repository:

public interface ProductRepository extends JpaRepository<Product, Long> {}

🔹 8. What are records in Java 17 and how can they be used in Spring Boot?

✅ Answer:

Records are immutable data classes:

public record ProductDTO(Long id, String name) {}

Use in controller responses:

@GetMapping

public List<ProductDTO> getProducts() {

return List.of(new ProductDTO(1L, "Laptop"));

}

🔹 9. How to validate a request in Spring Boot using Java Bean Validation?

✅ Example:

@RestController

public class UserController {

@PostMapping("/users")

public ResponseEntity<String> save(@Valid @RequestBody UserDto user) {

return ResponseEntity.ok("Valid");

}

}

class UserDto {

@NotBlank

private String name;

}

🔹 10. How to secure Spring Boot REST API using Spring Security + JWT?

✅ Key Components:

• UsernamePasswordAuthenticationFilter

• JWT token utility

• Custom UserDetailsService

@Configuration

@EnableWebSecurity

public class SecurityConfig {

@Bean

public SecurityFilterChain security(HttpSecurity http) throws Exception {

http.csrf().disable()

.authorizeHttpRequests()

.requestMatchers("/auth/**").permitAll()

.anyRequest().authenticated();

return http.build();

}

}