服务限流之令牌桶算法(注解版本)

1. 定义注解

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

    /**
     * 令牌产生的速率
     *
     * @return
     */
    double permitsPerSecond();

    /**
     * 客户端等待的毫秒数
     *
     * @return
     */
    int permits();
}

2.实现方法拦截

@Aspect
@Component
public class RateLimiterAOP {

    private Map rateLimiterMap = new ConcurrentHashMap<>();

    @Pointcut("execution(public * com.example.nginx.controller.*.*(..))")
    public void pointCut() {
    }

    @Around("pointCut()")
    public Object around(ProceedingJoinPoint proceedingJoinPoint) throws Throwable {
        //判断方法上是否有指定注解
        MethodSignature methodSignature = (MethodSignature) proceedingJoinPoint.getSignature();
        Method method = methodSignature.getMethod();
        Annotation annotation = method.getDeclaredAnnotation(CusRateLimiter.class);
        if (annotation == null) {
            return proceedingJoinPoint.proceed();
        }
        CusRateLimiter cusRateLimiter = (CusRateLimiter) annotation;
        //以请求的url为单位, 来生成令牌桶
        ServletRequestAttributes attributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
        String requestURI = attributes.getRequest().getRequestURI();
        RateLimiter rateLimiter = null;
        if (rateLimiterMap.containsKey(requestURI)) {
            rateLimiter = rateLimiterMap.get(requestURI);
        } else {
            rateLimiter = RateLimiter.create(cusRateLimiter.permitsPerSecond());
            rateLimiterMap.put(requestURI, rateLimiter);
        }
        //获取令牌
        if (rateLimiter.tryAcquire(cusRateLimiter.permits(), TimeUnit.MILLISECONDS)) {
            return proceedingJoinPoint.proceed();
        }
        failback();
        return null;
    }

    /**
     * 服务降级方法
     *
     * @throws IOException
     */
    private void failback() throws IOException {
        ServletRequestAttributes attributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
        HttpServletResponse response = attributes.getResponse();
        response.setHeader("Content-type", "text/html;charset=UTF-8");
        try (PrintWriter writer = response.getWriter();) {
            writer.println("服务器忙, 请稍后重试");
        }
    }
}