Clean ⢠Professional
Spring Boot applications follow a layered and modular architecture, which ensures that every part of your application has a clear responsibility. The Request ā Response lifecycle shows how a client request flows through these layers until a response is returned.
Understanding this helps you debug issues faster, write better code, and design scalable applications.
This lifecycle can be divided into 8 main/core steps, which cover the essential flow from when a client sends a request to when the response is sent back:

Everything starts when a client (browser, mobile app, or API consumer) sends an HTTP request to the Spring Boot application.
Example Request:
GET /users/123 HTTP/1.1
Host: localhost:8080
Spring Boot comes with embedded servers like Tomcat (default), Jetty, or Undertow.
Responsibilities of the Embedded Server:
ā” Why Embedded Servers Matter:
You donāt need to install or configure an external server manually. Your app is self-contained and production-ready.
The DispatcherServlet is the heart of Spring MVC. It manages how requests are routed in the application.
Key Tasks:
Internal Flow:
DispatcherServlet ā HandlerMapping ā Controller ā View/Response
Controllers are annotated with @RestController or @Controller.
Responsibilities:
@RequestParam, @PathVariable).@RequestBody).@Valid, @Validated).@ExceptionHandler, @ControllerAdvice).Example:
@RestController
@RequestMapping("/users")
public class UserController {
private final UserService userService;
public UserController(UserService userService) {
this.userService = userService;
}
@GetMapping("/{id}")
public ResponseEntity<User> getUser(@PathVariable Long id) {
User user = userService.getUserById(id);
return ResponseEntity.ok(user);
}
}
ā” Key Point: Controllers are only responsible for handling requests and sending responses, not business logic.
The Service Layer (@Service) contains all business logic.
Responsibilities:
@Transactional).Example:
@Service
public class UserService {
private final UserRepository userRepository;
public UserService(UserRepository userRepository) {
this.userRepository = userRepository;
}
public User getUserById(Long id) {
return userRepository.findById(id)
.orElseThrow(() -> new ResourceNotFoundException("User not found"));
}
}
Repositories (@Repository) interact with the database.
Responsibilities:
Example:
public interface UserRepository extends JpaRepository<User, Long> {}
Spring Boot auto-configures repositories using Spring Data JPA, so you donāt need boilerplate SQL or JDBC code.
The database layer is the actual storage system.
ā” Benefit: Minimal manual configuration, fully managed by Spring Boot.
After the service and repository layers finish processing:
ResponseEntity or JSON object.Response Example:
{
"id": 123,
"name": "John Doe",
"email": "[email protected]"
}
Spring Boot simplifies the lifecycle with:
Client ā Embedded Server ā Filter Chain ā DispatcherServlet ā HandlerMapping ā Handler Interceptors ā Controller ā Service ā Repository ā Database ā View Resolution / Message Conversion ā Response Generation ā Embedded Server ā Client
ā” This flow ensures modularity, scalability, and clean separation of concerns, making Spring Boot ideal for modern web applications and microservices.
The Spring Boot Request ā Response lifecycle is well-structured and highly modular. Each component has a clear responsibility, which allows for: