Spring Web Request Lifecycle

Spring Web Request Lifecycle — describes the sequence of steps an HTTP request goes through in a Spring (Boot) application from arrival to response.

🧩 Lifecycle Steps

1. Client sends HTTP request
   Browser, mobile app, or client sends request to the server.
2. Servlet Container (Tomcat/Jetty)
   The request hits the Servlet container, which delegates it to DispatcherServlet.
3. DispatcherServlet
   • Central Spring MVC component.
   • Receives all incoming requests (front controller).
   • Dispatches to appropriate controllers via HandlerMapping.
4. Handler Mapping
   Determines which controller method (@RequestMapping) will handle the request.
5. Handler Adapter
   Invokes the controller method and prepares the return value.
6. Controller (@Controller / @RestController)
   Processes business logic and returns ModelAndView or object.
7. View Resolver (for @Controller)
   If using templates (Thymeleaf, JSP), resolves which view to render.
   If @RestController, object is converted to JSON via HttpMessageConverter.
8. Interceptors & Filters
   • Filter → runs before DispatcherServlet.
   • HandlerInterceptor → preHandle, postHandle, afterCompletion around controller execution.
   • ExceptionHandler → handles errors.
9. Response to Client
   Response is serialized (JSON/HTML) and sent back via the Servlet container.

🧠 Key Points

• Filters → Servlet container level (pre/post request).
• Interceptors → Spring MVC level (controller execution).
• DispatcherServlet → heart of Spring Web.
• HttpMessageConverters → transform objects to JSON/XML automatically.