Spring MVC核心原理深度剖析:从请求到响应的魔法解密

<servlet>
    <servlet-name>dispatcher</servlet-name>
    <servlet-class>
        org.springframework.web.servlet.DispatcherServlet
    </servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>dispatcher</servlet-name>
    <url-pattern>/</url-pattern>
</servlet-mapping>

@Bean
public ViewResolver viewResolver() {
    InternalResourceViewResolver resolver = new InternalResourceViewResolver();
    resolver.setPrefix("/WEB-INF/views/");
    resolver.setSuffix(".jsp");
    return resolver;
}

@RestController
@RequestMapping("/api/users")
public class UserController {
    // 依赖注入服务层
    private final UserService userService;
    public UserController(UserService userService) {
        this.userService = userService;
    }
    @GetMapping("/{userId}")
    public ResponseEntity<UserDTO> getUser(@PathVariable Long userId) {
        // 调用服务层获取数据
        UserDTO user = userService.getUserById(userId);
        // 返回响应实体（包含状态码和响应头控制能力）
        return ResponseEntity.ok()
                .cacheControl(CacheControl.maxAge(30, TimeUnit.MINUTES))
                .body(user);
    }
    @PostMapping
    public ResponseEntity<Void> createUser(@Valid @RequestBody UserCreateRequest request) {
        // 处理创建用户逻辑
        Long newUserId = userService.createUser(request);
        // 返回创建成功的响应
        URI location = ServletUriComponentsBuilder.fromCurrentRequest()
                .path("/{id}")
                .buildAndExpand(newUserId)
                .toUri();
        return ResponseEntity.created(location).build();
    }
}

@ControllerAdvice
public class GlobalExceptionHandler {
    private static final Logger logger = LoggerFactory.getLogger(GlobalExceptionHandler.class);
    // 处理数据验证异常
    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<ErrorResponse> handleValidationException(
            MethodArgumentNotValidException ex) {
        List<String> errors = ex.getBindingResult()
                .getFieldErrors()
                .stream()
                .map(FieldError::getDefaultMessage)
                .collect(Collectors.toList());
        ErrorResponse response = new ErrorResponse("VALIDATION_ERROR", "参数验证失败", errors);
        return ResponseEntity.badRequest().body(response);
    }
    // 处理业务逻辑异常
    @ExceptionHandler(BusinessException.class)
    public ResponseEntity<ErrorResponse> handleBusinessException(
            BusinessException ex) {
        ErrorResponse response = new ErrorResponse(ex.getCode(), ex.getMessage());
        return ResponseEntity.status(HttpStatus.CONFLICT).body(response);
    }
    // 处理所有未捕获异常
    @ExceptionHandler(Exception.class)
    public ResponseEntity<ErrorResponse> handleAllException(Exception ex) {
        logger.error("系统异常: {}", ex.getMessage(), ex);
        ErrorResponse response = new ErrorResponse("SYSTEM_ERROR", "系统繁忙，请稍后再试");
        return ResponseEntity.internalServerError().body(response);
    }
}

public class PerformanceMonitorInterceptor implements HandlerInterceptor {
    private static final ThreadLocal<Long> startTime = new ThreadLocal<>();
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
        startTime.set(System.currentTimeMillis());
        return true;
    }
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, 
            Object handler, ModelAndView modelAndView) {
        // 记录请求处理耗时
        long duration = System.currentTimeMillis() - startTime.get();
        request.setAttribute("PROCESS_TIME_MS", duration);
        // 添加自定义响应头
        response.addHeader("X-Process-Time", duration + "ms");
        // 清理ThreadLocal
        startTime.remove();
    }
}

@Configuration
public class WebConfig implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new PerformanceMonitorInterceptor())
                .addPathPatterns("/api/**")  // 仅拦截API路径
                .excludePathPatterns("/api/health"); // 排除健康检查
    }
}

public class ApiResponse<T> {
    private String code;
    private String message;
    private T data;
    private long timestamp = System.currentTimeMillis();
    
    // 构造器、静态工厂方法等
}