MVC & Spring MVC

MVC

• MVC is a design pattern, not a specific technology. MVC = Model + View + Controller
  • Model：data + business state (also includes DTO,entities,domain objects)
  • View：what user sees
  • Controller：receives request, calls business logic

Spring MVC

• Spring MVC is a web application framework, the part of Spring that handles HTTP requests (web layer) So in your backend:

  Spring Boot
     ↓
  Spring MVC (web layer)
     ↓
  Your Controller code

• Spring MVC = DispatcherServlet + Controller mapping + Parameter binding + Response rendering

  • It is responsible for: receiving HTTP requests, routing them to controllers, binding parameters. returning responses (JSON / view)

  Core components inside Spring MVC

  Component	Role
  DispatcherServlet	entry point
  HandlerMapping	find controller
  HandlerAdapter	execute method
  Controller	business entry
  ViewResolver	render response

  Full request flow (Spring MVC core)

  Client (browser / frontend)
       ↓
  DispatcherServlet  ← ⭐ core center
       ↓
  HandlerMapping
       ↓
  Controller
       ↓
  Service (business logic)
       ↓
  Database / External API
       ↓
  Return Response (JSON / View)

  1. Request arrives

     POST /coupon/claim

  2. DispatcherServlet receives it

     • This is the entry point of Spring MVC
     • why DispatcherServlet is important?
       • All HTTP requests go through dispatcherServlet, it enables: unified request handling, interceptor support, exception handling, logging, security filters
     • Who creates DispatcherServlet?
       • In old Spring MVC (manual config) You had to configure it yourself:

         <servlet>
         <servlet-name>dispatcher</servlet-name>
         <servlet-class>DispatcherServlet</servlet-class>
         </servlet>

       • In Spring Boot
         • You do NOT create it manually, Spring Boot does it automatically using auto-configuration
         • Because you added:

           spring-boot-starter-web

           Spring Boot:
           • detects web dependency
           • creates DispatcherServlet
           • registers it
           • maps it to /

  3. Handler Mapping

     Spring finds:@PostMapping("/coupon/claim")→ maps映射 request to method

  4. Handler Adapter适配器

     Responsible for:

     • calling controller method
     • preparing parameters

  5. Parameter binding绑定

     @RequestBody ClaimRequest req    JSON → Java object

  6. Execute Controller

     couponService.claim(req);

  7. Return result

     return "ok";

  8. View resolution / JSON conversion

     • If @RestController → JSON
     • If @Controller → HTML view

  9. Response sent

     HTTP 200 OK

What is Interceptor ?

• A Spring MVC component that intercepts HTTP requests before and after controller execution.

  Request
    ↓
  DispatcherServlet
    ↓
  preHandle()   ← interceptor (before controller)
    ↓
  Controller
    ↓
  postHandle()  ← interceptor (after controller, before response)
    ↓
  afterCompletion() ← after everything
    ↓
  Response

• So in real cases, it used to: 1.Login check 2.Permission check 3.Logging 4.Performance monitoring 5.Token monitoring(JWT)