1 需求分析/图解
Redis 除了做缓存，还能干很多很多事情：分布式锁、限流、处理请求接口幂等性
- 完成接口限流-防止某个用户频繁的请求秒杀接口
- 比如在短时间内，频繁点击抢购，我们需要给用户访问频繁的提示防止一直刷一个接口
2 简单接口限流
- 使用简单的 Redis 计数器, 完成接口限流防刷
- 除了计数器算法，也有其它的算法来进行接口限流, 比如漏桶算法和令牌桶算法
- 令牌桶算法, 相对比较主流, 可以关注一下.Java高并发系统限流算法的应用：
- 代码实现
@RequestMapping(value = "/path", method = RequestMethod.GET) @ResponseBody public RespBean getPath(User user, Long goodsId, String captcha, HttpServletRequest request) { if (user == null) { return RespBean.error(RespBeanEnum.SESSION_ERROR); } // 秒杀 v7.0 计数器 redis,5 秒内访问超过 5 次，就认为是刷接口 String uri = request.getRequestURI(); ValueOperations valueOperations = redisTemplate.opsForValue(); Integer count = (Integer) valueOperations.get(uri + ":" + user.getId()); if (count == null) { //用户在5秒内没有访问过该接口，key=uri + ":" + user.getId() value = 1 valueOperations.set(uri + ":" + user.getId(), 1, 5, TimeUnit.SECONDS); } else if (count < 5) { //用户在5秒内访问过该接口，但访问次数<5则，进行+1 valueOperations.increment(uri + ":" + user.getId()); } else { //用户在5秒内访问次数>5，则对接口进行限流，提示用户访问过于频繁 return RespBean.error(RespBeanEnum.ACCESS_LIMIT_REACHED); } //验证用户输入的验证码 boolean check = orderService.checkCaptcha(user, goodsId, captcha); if (!check) { return RespBean.error(RespBeanEnum.CAPTCHA_ERROR); } //创建真正的地址 String url = orderService.createPath(user, goodsId); return RespBean.success(url); }
3 基于注解实现接口限流
- 自定义注解@AccessLimit, 提高接口限流功能通用性 , 减少冗余代码, 同时也减少业
务代码入侵
- 思路分析-简单示意图
代码实现
自定义限流注解 /** * 限流注解 */ @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.METHOD) public @interface AccessLimit { //定义限制多少秒内进行限流 int second(); //定义多少秒内，接口最大访问次数 int maxCount(); //接口是否需要验证登录信息 boolean needLogin() default true; } 限流拦截器 @Component public class AccessLimitInterceptor implements HandlerInterceptor { @Resource private UserService userService; @Resource private RedisTemplate redisTemplate; /** * 1.preHandle 方法在目标方法执行前被执行 * 2.如果返回fasle则不在执行目标方法 * * @param request * @param response * @param handler * @return * @throws Exception */ @Override public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { if (handler instanceof HandlerMethod) { User user = getUser(request, response); UserContext.setUser(user); HandlerMethod handlerMethod = (HandlerMethod) handler; AccessLimit accessLimit = handlerMethod.getMethodAnnotation(AccessLimit.class); if (accessLimit == null) { //没有，直接放行 return true; } boolean needLogin = accessLimit.needLogin(); int limitCount = accessLimit.maxCount(); int second = accessLimit.second(); if (needLogin && user == null) { render(response, RespBeanEnum.SESSION_ERROR); return false; } String uri = request.getRequestURI(); ValueOperations valueOperations = redisTemplate.opsForValue(); Integer count = (Integer) valueOperations.get(uri + ":" + user.getId()); if (count == null) { //用户在5秒内没有访问过该接口，key=uri + ":" + user.getId() value = 1 valueOperations.set(uri + ":" + user.getId(), 1, second, TimeUnit.SECONDS); } else if (count < limitCount) { //用户在5秒内访问过该接口，但访问次数<5则，进行+1 valueOperations.increment(uri + ":" + user.getId()); } else { //用户在5秒内访问次数>5，则对接口进行限流，提示用户访问过于频繁 //返回错误信息 render(response, RespBeanEnum.ACCESS_LIMIT_REACHED); return false; } } return true; } /** * 渲染错误信息返回 * * @param response * @param respBeanEnum */ private void render(HttpServletResponse response, RespBeanEnum respBeanEnum) throws IOException { System.out.println("render-" + respBeanEnum.getMessage()); response.setContentType("application/json"); response.setCharacterEncoding("utf-8"); PrintWriter out = response.getWriter(); RespBean error = RespBean.error(respBeanEnum); out.write(new ObjectMapper().writeValueAsString(error)); out.flush(); out.close(); } //获取当前用户 private User getUser(HttpServletRequest request, HttpServletResponse response) { String ticket = CookieUtil.getCookieValue(request, "userTicket"); if (!StringUtils.hasText(ticket)) { return null; } return userService.getUserByTicket(request, response, ticket); } } 测试方法 @RequestMapping(value = "/path", method = RequestMethod.GET) @ResponseBody /** * @AccessLimit(second = 5, maxCount = 5, needLogin = true) * 1. 使用注解的方式完成通用的接口防刷功能 * 2. second = 5, maxCount = 5 5 秒内,最多 5 次请求,否性进行限流 * 3. needLogin = true 表示需要登录 */ @AccessLimit(second = 5, maxCount = 5, needLogin = true) public RespBean getPath(User user, Long goodsId, String captcha, HttpServletRequest request) { if (user == null) { return RespBean.error(RespBeanEnum.SESSION_ERROR); } // 秒杀 v7.0 计数器 redis,5 秒内访问超过 5 次，就认为是刷接口 String uri = request.getRequestURI(); ValueOperations valueOperations = redisTemplate.opsForValue(); Integer count = (Integer) valueOperations.get(uri + ":" + user.getId()); if (count == null) { //用户在5秒内没有访问过该接口，key=uri + ":" + user.getId() value = 1 valueOperations.set(uri + ":" + user.getId(), 1, 5, TimeUnit.SECONDS); } else if (count < 5) { //用户在5秒内访问过该接口，但访问次数<5则，进行+1 valueOperations.increment(uri + ":" + user.getId()); } else { //用户在5秒内访问次数>5，则对接口进行限流，提示用户访问过于频繁 return RespBean.error(RespBeanEnum.ACCESS_LIMIT_REACHED); } //验证用户输入的验证码 boolean check = orderService.checkCaptcha(user, goodsId, captcha); if (!check) { return RespBean.error(RespBeanEnum.CAPTCHA_ERROR); } //创建真正的地址 String url = orderService.createPath(user, goodsId); return RespBean.success(url); } //用来存储拦截器获取的 user 对象 public class UserContext { //每个线程都有自己的 threadlocal，存在这里不容易混乱,线程安全 private static ThreadLocal<User> userHolder = ThreadLocal.withInitial(() -> null); public static void setUser(User user) { userHolder.set(user); } public static User getUser() { return userHolder.get(); } } 注册拦截器 @EnableWebMvc @Configuration public class WebConfig implements WebMvcConfigurer { @Resource private UserArgumentResolver userArgumentResolver; @Resource private AccessLimitInterceptor accessLimitInterceptor; /** * 注册拦截器 */ @Override public void addInterceptors(InterceptorRegistry registry) { registry.addInterceptor(accessLimitInterceptor); } /** * 静态资源加载 * * @param registry */ @Override public void addResourceHandlers(ResourceHandlerRegistry registry) { registry.addResourceHandler("/**").addResourceLocations("classpath:/static/"); } /** * 将自定义参数解析器添加到解析器列表中 * * @param resolvers */ @Override public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) { resolvers.add(userArgumentResolver); } }
