Spring Boot 中的请求生命周期是如何工作的？

Servlet container (Tomcat)
   ▼
Filter chain  ── (CharacterEncoding, Security, CORS, ...)
   ▼
DispatcherServlet  ── front controller
   ▼
HandlerMapping  ── 找到 @Controller 方法
   ▼
HandlerInterceptor.preHandle
   ▼
Argument resolvers  ── bind @RequestBody / @PathVariable / @RequestParam
   ▼
Controller method  ── 你的逻辑 → 返回 object 或 ResponseEntity
   ▼
HandlerInterceptor.postHandle
   ▼
HttpMessageConverter / ViewResolver  ── serialize 成 JSON 或 render view
   ▼
HandlerInterceptor.afterCompletion → Response ──▶ client

// 4/7/8. interceptor
public class TimingInterceptor implements HandlerInterceptor {
    public boolean preHandle(HttpServletRequest req, HttpServletResponse res, Object h) {
        req.setAttribute("started", System.nanoTime());
        return true;                       // false = 短路
    }
}

// 6. controller
@RestController
class ItemController {
    @GetMapping("/items/{id}")            // 3. mapping
    ResponseEntity<Item> show(@PathVariable Long id) {  // 5. argument resolution
        return ResponseEntity.ok(service.find(id));      // 7. serialize 成 JSON
    }
}