Spring Boot is built on top of Spring framework and provides opinionated defaults to get started quickly.

Spring Boot Starters are dependency descriptors that include a set of convenient dependency management for specific functionality.
Common starters:

• spring-boot-starter-web: Web applications with REST APIs
• spring-boot-starter-data-jpa: JPA with Hibernate
• spring-boot-starter-security: Spring Security
• spring-boot-starter-test: Testing framework with JUnit, Mockito
• spring-boot-starter-actuator: Monitoring and management
• spring-boot-starter-data-redis: Redis data access
• spring-boot-starter-mail: Email support

@SpringBootApplication is a convenience annotation that combines three annotations:

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

Equivalent to:

• @Configuration: Indicates configuration class
• @EnableAutoConfiguration: Enables auto-configuration
• @ComponentScan: Enables component scanning in current package and sub-packages

All are specializations of @Component for specific layers:

• @Component: Generic stereotype for any Spring-managed component
• @Service: Business logic layer components
• @Repository: Data access layer components (adds exception translation)
• @Controller: Presentation layer components for handling HTTP requests

@Service
public class UserService { }
@Repository
public class UserRepository { }
@Controller
public class UserController { }

Functionally similar, but provide better semantic meaning and potential for additional features.

@RestController
@RequestMapping("/api/users")
public class UserController {
    @Autowired
    private UserService userService;
    @GetMapping
    public List<User> getAllUsers() {
        return userService.findAll();
    }
    @GetMapping("/{id}")
    public User getUser(@PathVariable Long id) {
        return userService.findById(id);
    }
    @PostMapping
    public User createUser(@RequestBody User user) {
        return userService.save(user);
    }
    @PutMapping("/{id}")
    public User updateUser(@PathVariable Long id, @RequestBody User user) {
        return userService.update(id, user);
    }
    @DeleteMapping("/{id}")
    public void deleteUser(@PathVariable Long id) {
        userService.delete(id);
    }
}