前言

spring cloud gateway作为一种简单有效的统一的API路由管理方式，为我们限流措施提供了一个有效的入口。

一. 限流算法

本文从常用的令牌桶限流算法说起，看如何让在网关中做请求限制。羊会在后续文章中和大家探讨一下一些限流算法，并会在后续文章中讨论下分布式环境中如何在网关限流，请大家持续关注我的文章。

二. 创建工程

2.1 创建一个spring cloud gateway工程
（相信大家早已不陌生，此处省略）
2.2 引入Bucket4j依赖

<dependency>
        <groupId>com.github.vladimir-bukhtoyarov</groupId>
        <artifactId>bucket4j-core</artifactId>
        <version>4.4.1</version>
    </dependency>

2.3 创建网关过滤器

@Component
@Slf4j
@RefreshScope
public class IpRegisterFilter implements GlobalFilter, Ordered {  

    public static final String WARNING_MSG = "访问太频繁了!";

    public static final Map<String, Bucket> LOCAL_CACHE = new ConcurrentHashMap<>();

    // 令牌桶初始容量3    
    private Integer CAPACITY = 3;

    // 补充桶的时间间隔，即60秒补充一次    
    private long PERIOD = 60;

    // 每次补充token的个数
    public static final long REPLENISH = 1;


    @Override
    public Mono<Void> filter(ServerWebExchange serverWebExchange, GatewayFilterChain gatewayFilterChain) {
        ServerHttpRequest request = serverWebExchange.getRequest();
        ServerHttpResponse response = serverWebExchange.getResponse();

        if (request.getURI().getPath().contains( "/你的path" )) {
            String ip = request.getRemoteAddress().getHostString();
            log.info( "访问IP为:{}", ip );

            Bucket bucket = LOCAL_CACHE.computeIfAbsent( ip, k -> createNewBucket( ip ) );

            log.info( "IP:{} ,令牌通可用的Token数量:{} ", ip, bucket.getAvailableTokens() );

            if (bucket.tryConsume( 1 )) {
                // 直接放行
                return gatewayFilterChain.filter( serverWebExchange );
            } else {
                //指定编码
                response.getHeaders().add( "Content-Type", "text/plain;charset=UTF-8" );
                response.setStatusCode( HttpStatus.FORBIDDEN ); // 状态码
                byte[] data = WARNING_MSG.getBytes( StandardCharsets.UTF_8 );
                DataBuffer wrap = response.bufferFactory().wrap( data );
                return response.writeWith( Mono.just( wrap ) );
            }
        }
        return gatewayFilterChain.filter( serverWebExchange );           
    }

   
    @Override
    public int getOrder() {
        return 0;
    }

    private Bucket createNewBucket(String ip) {
        Duration replenishDuration = Duration.ofSeconds( PERIOD );
        Refill refill = Refill.of( REPLENISH, replenishDuration );
        Bandwidth limit = Bandwidth.classic( CAPACITY, refill );
        return Bucket4j.builder().addLimit( limit ).build();
    }
}

至此，关键部分已完成。相信大家看到限流桶放在了map里，无法在多实例里应用。不要担心，请关注我后续文章，我会和大家探讨下如何在分布式环境中应用限流。