基于自定义注解实现拦截器

左手的ㄟ右手 2022-11-20 08:06 258阅读 0赞

上一篇文章写了怎么实现自定义注解

[https://blog.csdn.net/qq\_29569183/article/details/109310967][https_blog.csdn.net_qq_29569183_article_details_109310967]

### 在个拦截器中解析并使用注解 ###

@Target({ElementType.METHOD})
    @Retention(RetentionPolicy.RUNTIME)
    public @interface ApiIdempotent {
    }

**下面代码主要分析下如何分析注解**

**1.handler转换为HandlerMethod 对象**

HandlerMethod handlerMethod = (HandlerMethod) handler;

**2.获取HandlerMethod 对象的Method属性**

** ** Method method = handlerMethod.getMethod();

**3.获取Method上的注解 **

ApiIdempotent methodAnnotation = method.getAnnotation(ApiIdempotent.class)

**4.判断注解是否存在，做后续的逻辑处理**

拦截器的使用就不赘述了，实现HandlerInterceptor接口重写方法，再基于WebMvcConfigurer 做配置使拦截器生效即可。

public class ApiIdempotentInterceptor implements HandlerInterceptor {
    
        private static final String VERSION_NAME = "version";
    
        private RedisTemplate<String, Object> redisTemplate;
    
    
        public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
    
            //如果不是一个接口请求（比如静态资源类的），那么handler就不是一个HandlerMethod
            if (!(handler instanceof HandlerMethod)) {
                return true;
            }
    
            HandlerMethod handlerMethod = (HandlerMethod) handler;
            Method method = handlerMethod.getMethod();
    
            //获取目标方法上的幂等注解
            ApiIdempotent methodAnnotation = method.getAnnotation(ApiIdempotent.class);
            if (methodAnnotation != null) {
                // 幂等性校验, 校验通过则放行, 校验失败则抛出异常, 并通过统一异常处理返回友好提示
                checkApiIdempotent(request);
            }
            return true;
        }
    
    
        private void checkApiIdempotent(HttpServletRequest request) {
            String version = request.getHeader(VERSION_NAME);
            if (StringUtils.isBlank(version)) {// header中不存在token
                version = request.getParameter(VERSION_NAME);
                if (StringUtils.isBlank(version)) {// parameter中也不存在token
                    throw new IllegalArgumentException("无效的参数");
                }
            }
            if (!redisTemplate.hasKey(version)) {
                throw new IllegalArgumentException("不存在对应的参数");
            }
            Boolean bool = redisTemplate.delete(version);
            if (!bool) {
                throw new IllegalArgumentException("没有删除对应的version");
            }
        }
    
        public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
    
        }
    
        public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
    
        }
    
        public ApiIdempotentInterceptor(RedisTemplate<String, Object> redisTemplate) {
            this.redisTemplate = redisTemplate;
        }
    }

[https_blog.csdn.net_qq_29569183_article_details_109310967]: https://blog.csdn.net/qq_29569183/article/details/109310967