Spring Cloud Alibaba学习笔记（20） - Spring Cloud Gateway 内置的全局过滤器

参考：https://cloud.spring.io/spring-cloud-static/Greenwich.SR2/single/spring-cloud.html#_global_filters

Combined Global Filter and GatewayFilter Ordering	对过滤器执行顺序进行排序
Forward Routing Filter	用于本地forward，也就是将请求在Gateway服务内进行转发，而不是转发到下游服务
LoadBalancerClient Filter	整合Ribbon实现负载均衡
Netty Routing Filter	使用Netty的 HttpClient 转发http、https请求
Netty Write Response Filter	将代理响应写回网关的客户端侧
RouteToRequestUrl Filter	将从request里获取的原始url转换成Gateway进行请求转发时所使用的url
Websocket Routing Filter	使用Spring Web Socket将转发 Websocket 请求
Gateway Metrics Filter	整合监控相关，提供监控指标
Marking An Exchange As Routed	防止重复的路由转发

Combined Global Filter and GatewayFilter Ordering

示例代码:

@Bean
@Order(-1)
public GlobalFilter a() {
    return (exchange, chain) -> {
        log.info("first pre filter");
        return chain.filter(exchange).then(Mono.fromRunnable(() -> {
            log.info("third post filter");
        }));
    };
}

@Bean
@Order(0)
public GlobalFilter b() {
    return (exchange, chain) -> {
        log.info("second pre filter");
        return chain.filter(exchange).then(Mono.fromRunnable(() -> {
            log.info("second post filter");
        }));
    };
}

@Bean
@Order(1)
public GlobalFilter c() {
    return (exchange, chain) -> {
        log.info("third pre filter");
        return chain.filter(exchange).then(Mono.fromRunnable(() -> {
            log.info("first post filter");
        }));
    };
}

返回结果：

first pre filter
second pre filter
third pre filter
first post filter
second post filter
third post filter

Forward Routing Filter

PS：所谓 url scheme 简单来说就是 url 中的协议部分，例如http、https、ws等。自定义的 scheme 通常用于标识该url的行为，例如app开发中通常使用url scheme来跳转页面

LoadBalancerClient Filter

这个Filter是用来整合Ribbon的，其核心就是解析 scheme 为lb的 url，以此获取微服务的名称，然后再通过Ribbon获取实际的调用地址。

示例配置：

spring:
  cloud:
    gateway:
      routes:
      - id: myRoute
        uri: lb://service
        predicates:
        - Path=/service/**

Netty Routing Filter

Netty Write Response Filter

RouteToRequestUrl Filter

Websocket Routing Filter

示例配置：

spring:
  cloud:
    gateway:
      routes:
      # SockJS route
      - id: websocket_sockjs_route
        uri: http://localhost:3001
        predicates:
        - Path=/websocket/info/**
      # Normwal Websocket route
      - id: websocket_route
        uri: ws://localhost:3001
        predicates:
        - Path=/websocket/**

Gateway Metrics Filter

PS：Prometheus是一款监控工具，Grafana是一款监控可视化工具；Spring Boot Actuator可与这两款工具进行整合。

Marking An Exchange As Routed

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