Spring MVC 面试题常问｜高频考点深度解析

// 请求：GET /api/users/1024
// 1. DispatcherServlet 拦截
// 2. HandlerMapping 找到：@GetMapping("/api/users/{id}")
// 3. HandlerAdapter 调用方法：
public ResponseEntity<User> getUser(@PathVariable("id") Long userId) {
    User user = userService.findById(userId); // 调用 Service
    return ResponseEntity.ok(user); // 返回 JSON（含 @ResponseBody）
}
// 4. HttpMessageConverter 将 User 对象转为 JSON 字符串
// 5. 写入响应体，完成响应

@PostMapping("/api/users")
public ResponseEntity<User> createUser(
    @Valid @RequestBody UserCreateRequest request,  // JSON 请求体
    @RequestHeader("X-Client-Version") String clientVersion, // 请求头
    @CookieValue(value = "JSESSIONID", required = false) String sessionId // Cookie
) {
    // request 对象含字段：username, email, age（自动校验）
    // clientVersion = "2.3.1"
    // sessionId = "ABC123..."
    return ResponseEntity.ok(userService.save(request));
}

@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
    @Bean
    public ViewResolver thymeleafViewResolver() {
        ThymeleafViewResolver resolver = new ThymeleafViewResolver();
        resolver.setTemplateEngine(templateEngine());
        resolver.setCharacterEncoding("UTF-8");
        return resolver;
    }
    @Bean
    public TemplateEngine templateEngine() {
        SpringTemplateEngine engine = new SpringTemplateEngine();
        engine.setTemplateResolver(templateResolver());
        return engine;
    }
    @Bean
    public ITemplateResolver templateResolver() {
        SpringResourceTemplateResolver resolver = new SpringResourceTemplateResolver();
        resolver.setPrefix("classpath:/templates/");
        resolver.setSuffix(".html");
        resolver.setTemplateMode("HTML");
        return resolver;
    }
}

@PostMapping("/upload")
public ResponseEntity<String> upload(@RequestParam("file") MultipartFile file) {
    String fileName = file.getOriginalFilename();
    file.transferTo(new File("/tmp/" + fileName));
    return ResponseEntity.ok("上传成功: " + fileName);
}

@RestControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(BindException.class)
    public ResponseEntity<Map<String, Object>> handleValidationException(BindException ex) {
        Map<String, Object> result = new HashMap<>();
        result.put("code", 400);
        result.put("message", "参数校验失败");
        result.put("errors", ex.getFieldErrors().stream()
            .map(e -> e.getField() + ": " + e.getDefaultMessage())
            .collect(Collectors.toList()));
        return ResponseEntity.badRequest().body(result);
    }
    @ExceptionHandler(Exception.class)
    public ResponseEntity<Map<String, Object>> handleException(Exception ex) {
        log.error("系统异常", ex);
        return ResponseEntity.status(500).body(Map.of(
            "code", 500,
            "message", "服务器内部错误"
        ));
    }
}

public class AuthInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
        String token = request.getHeader("Authorization");
        if (token == null || !token.startsWith("Bearer ")) {
            response.setStatus(401);
            response.setContentType("application/json");
            response.getWriter().write("{\"code\":401,\"message\":\"未授权\"}");
            return false;
        }
        // 验证 token（如 JWT 解析）
        return true;
    }
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) {
        // 可添加公共模型数据
    }
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
        // 记录请求耗时、异常日志
        log.info("请求完成: {} {}，耗时: {}ms", request.getMethod(), request.getRequestURI(),
            System.currentTimeMillis() - (Long)request.getAttribute("startTime"));
    }
}

@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new AuthInterceptor())
            .addPathPatterns("/api/**")  // 拦截路径
            .excludePathPatterns("/api/public/**"); // 排除路径
    }
}

// 1. 定义转换器
public class StringToLocalDateConverter implements Converter<String, LocalDate> {
    @Override
    public LocalDate convert(String source) {
        return LocalDate.parse(source, DateTimeFormatter.ofPattern("yyyy-MM-dd"));
    }
}
// 2. 注册转换器
@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
    @Override
    public void addFormatters(FormatterRegistry registry) {
        registry.addConverter(new StringToLocalDateConverter());
    }
}

@InitBinder
public void initBinder(WebDataBinder binder) {
    binder.registerCustomEditor(Date.class, new CustomDateEditor(
        new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"), true));
}

@PostMapping("/upload/multi")
public ResponseEntity<List<String>> uploadMulti(@RequestParam("files") List<MultipartFile> files) {
    List<String> fileNames = new ArrayList<>();
    for (MultipartFile file : files) {
        String fileName = UUID.randomUUID() + "-" + file.getOriginalFilename();
        file.transferTo(new File("/tmp/" + fileName));
        fileNames.add(fileName);
    }
    return ResponseEntity.ok(fileNames);
}

@GetMapping("/download/{fileName}")
public void download(@PathVariable String fileName, HttpServletResponse response) throws IOException {
    File file = new File("/tmp/" + fileName);
    response.setContentType("application/octet-stream");
    response.setHeader("Content-Disposition", "attachment; filename=" + URLEncoder.encode(fileName, "UTF-8"));
    response.setContentLength((int) file.length());
    Files.copy(file.toPath(), response.getOutputStream());
}

@GetMapping("/async")
public Callable<String> async() {
    return () -> {
        Thread.sleep(2000); // 模拟耗时操作
        return "处理完成";
    };
}