How Spring MVC Works Internally?

Front Controller Design Pattern

Spring MVC follows the Front Controller design pattern.

  • A Front Controller is a single controller that handles all incoming requests and sends back responses.
  • In Spring MVC, the DispatcherServlet acts as the Front Controller.

Step 1: Request to DispatcherServlet

  • First, when a user sends a request, it always comes to the DispatcherServlet.
  • Example: GET http://localhost:8080/home

Step 2: Handler Mappings

At application startup, Spring scans all @Controller classes and builds a Handler Mapping of all @RequestMapping methods. Example:

OrderController : path="/order", GET : create()
UserController  : path="/user",  GET : signup()
When a request comes in, Spring checks in the Handler Mappings:

  • If a match is not found : 404 Not Found
  • If a match is found : The respective controller method is executed

Step 3: Request Handling

  • The Handler (Controller method) processes the request.

  • It may return:

    • Data (JSON/XML) → in REST APIs (@ResponseBody)
    • Logical view name (for web apps with JSP/Thymeleaf)

Step 4: View Resolver

  • If the controller returns a view name, the ViewResolver maps it to an actual view file.
  • Controller returns "index" (a logical view name).
  • Spring adds the prefix + suffix: /WEB-INF/view/ + index + .jsp → /WEB-INF/view/index.jsp
  • Then, the view layer (JSP/Thymeleaf/HTML) is rendered and returned to the client.


Summary Flow

  • Request → DispatcherServlet (Front Controller)
  • DispatcherServlet → Handler Mapping (finds matching controller method)
  • Controller Method executes (returns data or view name)
  • DispatcherServlet → ViewResolver (resolves actual view)
  • Response sent back to client


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