让Controller支持对平铺参数执行数据校验（默认Spring MVC使用@Valid只能对JavaBean进行校验）【享学Spring】

@Configuration
@EnableWebMvc
public class WebMvcConfig extends WebMvcConfigurerAdapter {
    @Bean
    public MethodValidationPostProcessor mvcMethodValidationPostProcessor() {
        return new MethodValidationPostProcessor();
    }
}

@RestController
@RequestMapping
@Validated
public class HelloController {
    @PutMapping("/hello/id/{id}/status/{status}")
    public Object helloGet(@Max(5) @PathVariable Integer id, @Min(5) @PathVariable Integer status) {
        return "hello world";
    }
}

// 注意：此处只支持@RequesrMapping方式~~~~
public class ValidationInterceptor implements HandlerInterceptor, InitializingBean {
    @Autowired
    private LocalValidatorFactoryBean validatorFactoryBean;
    @Autowired
    private RequestMappingHandlerAdapter adapter;
    private List<HandlerMethodArgumentResolver> argumentResolvers;
    @Override
    public void afterPropertiesSet() throws Exception {
        argumentResolvers = adapter.getArgumentResolvers();
    }
    // 缓存
    private final Map<MethodParameter, HandlerMethodArgumentResolver> argumentResolverCache = new ConcurrentHashMap<>(256);
    private final Map<Class<?>, Set<Method>> initBinderCache = new ConcurrentHashMap<>(64);
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        // 只处理HandlerMethod方式
        if (handler instanceof HandlerMethod) {
            HandlerMethod method = (HandlerMethod) handler;
            Validated valid = method.getMethodAnnotation(Validated.class); //
            if (valid != null) {
                // 根据工厂，拿到一个校验器
                ValidatorImpl validatorImpl = (ValidatorImpl) validatorFactoryBean.getValidator();
                // 拿到该方法所有的参数们~~~  org.springframework.core.MethodParameter
                MethodParameter[] parameters = method.getMethodParameters();
                Object[] parameterValues = new Object[parameters.length];
                //遍历所有的入参：给每个参数做赋值和数据绑定
                for (int i = 0; i < parameters.length; i++) {
                    MethodParameter parameter = parameters[i];
                    // 找到适合解析这个参数的处理器~
                    HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);
                    Assert.notNull(resolver, "Unknown parameter type [" + parameter.getParameterType().getName() + "]");
                    ModelAndViewContainer mavContainer = new ModelAndViewContainer();
                    mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
                    WebDataBinderFactory webDataBinderFactory = getDataBinderFactory(method);
                    Object value = resolver.resolveArgument(parameter, mavContainer, new ServletWebRequest(request, response), webDataBinderFactory);
                    parameterValues[i] = value; // 赋值
                }
                // 对入参进行统一校验
                Set<ConstraintViolation<Object>> violations = validatorImpl.validateParameters(method.getBean(), method.getMethod(), parameterValues, valid.value());
                // 若存在错误消息，此处也做抛出异常处理 javax.validation.ConstraintViolationException
                if (!violations.isEmpty()) {
                    System.err.println("方法入参校验失败~~~~~~~");
                    throw new ConstraintViolationException(violations);
                }
            }
        }
        return true;
    }
    private WebDataBinderFactory getDataBinderFactory(HandlerMethod handlerMethod) {
        Class<?> handlerType = handlerMethod.getBeanType();
        Set<Method> methods = this.initBinderCache.get(handlerType);
        if (methods == null) {
            // 支持到@InitBinder注解
            methods = MethodIntrospector.selectMethods(handlerType, RequestMappingHandlerAdapter.INIT_BINDER_METHODS);
            this.initBinderCache.put(handlerType, methods);
        }
        List<InvocableHandlerMethod> initBinderMethods = new ArrayList<>();
        for (Method method : methods) {
            Object bean = handlerMethod.getBean();
            initBinderMethods.add(new InvocableHandlerMethod(bean, method));
        }
        return new ServletRequestDataBinderFactory(initBinderMethods, adapter.getWebBindingInitializer());
    }
    private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {
        HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);
        if (result == null) {
            for (HandlerMethodArgumentResolver methodArgumentResolver : this.argumentResolvers) {
                if (methodArgumentResolver.supportsParameter(parameter)) {
                    result = methodArgumentResolver;
                    this.argumentResolverCache.put(parameter, result);
                    break;
                }
            }
        }
        return result;
    }
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
    }
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
    }
}

    @Validated // 只需要方法处标注注解即可 非常简便
    @GetMapping("/hello/id/{id}/status/{status}")
    public Object helloGet(@Max(5) @PathVariable("id") Integer id, @Min(5) @PathVariable("status") Integer status) {
        return "hello world";
    }