秒杀下单接口限流

因为秒杀的特殊业务场景，生产场景下，还有可能要对秒杀下单接口进行访问流量控制，防止过多的请求进入到后端服务器。对于限流的实现方式，我们之前已经接触过通过nginx限流，网关限流。但是他们都是对一个大的服务进行访问限流，如果现在只是要对某一个服务中的接口方法进行限流呢？这里推荐使用google提供的guava工具包中的RateLimiter进行实现，其内部是基于令牌桶算法进行限流计算

1）添加依赖

<dependency>
  <groupId>com.google.guava</groupId>
  <artifactId>guava</artifactId>
  <version>28.0-jre</version>
</dependency>

2）自定义限流注解

@Inherited
@Documented
@Target({ElementType.METHOD, ElementType.FIELD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface AccessLimit {}

3）自定义切面类

@Component
@Scope
@Aspect
public class AccessLimitAop {

    @Autowired
    private HttpServletResponse httpServletResponse;

    private RateLimiter rateLimiter = RateLimiter.create(20.0);

    @Pointcut("@annotation(com.changgou.webSecKill.aspect.AccessLimit)")
    public void limit(){}

    @Around("limit()")
    public Object around(ProceedingJoinPoint proceedingJoinPoint){

        boolean flag = rateLimiter.tryAcquire();
        Object obj = null;

        try{
            if (flag){
                obj=proceedingJoinPoint.proceed();
            }else{
                String errorMessage = JSON.toJSONString(new Result(false,StatusCode.ERROR,"fail"));
                outMessage(httpServletResponse,errorMessage);
            }
        }catch (Throwable throwable) {
            throwable.printStackTrace();
        }
        return obj;

    }

    private void outMessage(HttpServletResponse response, String errorMessage) {

        ServletOutputStream outputStream = null;
        try {
            response.setContentType("application/json;charset=UTF-8");
            outputStream = response.getOutputStream();
            outputStream.write(errorMessage.getBytes("UTF-8"));
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                outputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

    }
}