限流可以在网关这一层做，比如Nginx、Openresty、kong、zuul、Spring Cloud Gateway等；也可以在应用层通过Aop这种方式去做限流。
一些限流组件，包括Redisson的令牌桶限流，Guava的RateLimiter(客户端限流)。Hystrix是客户端限流（参考彗安金科Java面试（部分） 或直接参考熔断器Hystrix 或JavaGuide—Java面试指北—高性能：负载均衡的常见算法有哪些？）。
网关层限流
网关层限流：gateway的限流基于Redis+Lua脚本1 2 :
Redisson分布式限流器RRateLimiter原理解析
单机限流：可Hystrix用线程池或Semaphore限流：
实例2：
RedisHystrixCommand.java :
public class RedisHystrixCommand<T> extends HystrixCommand<T> {
private static final Logger logger = new Logger("Hystrix");
private Callable<T> callable;
private T defaultResult;
private String opName;
/**
* constructor.
*/
public RedisHystrixCommand(String keyName, Callable<T> callable, T defaultResult,
String opName) {
// default timeout=1s, fallback when 50% or 20 requests in 10 seconds fail
super(Setter
.withGroupKey(HystrixCommandGroupKey.Factory.asKey(keyName))
.andCommandKey(HystrixCommandKey.Factory.asKey(keyName))
.andCommandPropertiesDefaults(HystrixCommandProperties.Setter()
.withExecutionIsolationStrategy(ExecutionIsolationStrategy.SEMAPHORE)
.withCircuitBreakerEnabled(true)));
this.callable = callable;
this.defaultResult = defaultResult;
this.opName = opName;
}
@Override
protected T run() throws Exception {
return callable.call();
}
@Override
protected T getFallback() {
logger.error("RedisCache {} fallback since executionTimeout, return {}",
opName, defaultResult);
return defaultResult;
}
}
RedisHelper.java:
public Long sadd(String key, String member) {
return new RedisHystrixCommand<>(getCommandKey(), () ->
getRedisClient().handle(redis -> redis.sadd(key, member))
.orElse(0L), 0L, "sadd").execute();
}