微服务-Gateway

案例搭建

官网地址

父Pom

<com.alibaba.cloud.version>2.2.8.RELEASEcom.alibaba.cloud.version>
<com.cloud.version>Hoxton.SR12com.cloud.version>
<com.dubbo.version>2.2.7.RELEASEcom.dubbo.version>
<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>com.alibaba.cloudgroupId>
            <artifactId>spring-cloud-alibaba-dependenciesartifactId>
            <version>${com.alibaba.cloud.version}version>
            <type>pomtype>
            <scope>importscope>
        dependency>
        <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-dependenciesartifactId>
            <version>${com.cloud.version}version>
            <type>pomtype>
            <scope>importscope>
        dependency>
        
        <dependency>
            <groupId>com.alibaba.cloudgroupId>
            <artifactId>spring-cloud-starter-dubboartifactId>
            <version>${com.dubbo.version}version>
        dependency>
    dependencies>

dependencyManagement>

工程POM

<dependency>
   <groupId>org.springframework.cloudgroupId>
   <artifactId>spring-cloud-starter-gatewayartifactId>
dependency>
<dependency>
   <groupId>com.alibaba.cloudgroupId>
   <artifactId>spring-cloud-starter-alibaba-nacos-discoveryartifactId>
dependency>

server:
  port: 9005
spring :
  application:
    name: gateway-server
  cloud:
    nacos:
      discovery:
        server-addr: ip:8848
    gateway:
      routes:
        - id: gateway-provider
          uri: http://127.0.0.1:8088
          predicates:
            - Path=/provider/**
          filters:
            - StripPrefix=1
        - id: gateway-consumer
          uri: http://127.0.0.1:8089
          predicates:
            - Path=/consumer/** 
          filters:
            - StripPrefix=1 #转发之前将路径前面的一个字符串去除 比如/consumer/echo  最终转发到服务是 http://127.0.0.1:8089/echo
        - id: gateway-lb
          uri: lb://openfeign-provider #负载均衡,填写nacos里面的服务名称
          predicates:
            - Path=/lb/**
          filters:
            - StripPrefix=1

启动一个普通的服务端和消费端，另外起一个有三台服务的集群，这些节点的搭建比较容易，可以看同目录笔记。
怎么做到负载均衡？怎么探索源码找到负载均衡？
org.springframework.cloud.gateway.filter.LoadBalancerClientFilter

public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
		URI url = exchange.getAttribute(GATEWAY_REQUEST_URL_ATTR);
		String schemePrefix = exchange.getAttribute(GATEWAY_SCHEME_PREFIX_ATTR);
		if (url == null
				|| (!"lb".equals(url.getScheme()) && !"lb".equals(schemePrefix))) {
			return chain.filter(exchange);
		}
		// preserve the original url
		addOriginalRequestUrl(exchange, url);

		if (log.isTraceEnabled()) {
			log.trace("LoadBalancerClientFilter url before: " + url);
		}
		// 选择实例
		final ServiceInstance instance = choose(exchange);

		if (instance == null) {
			throw NotFoundException.create(properties.isUse404(),
					"Unable to find instance for " + url.getHost());
		}

		URI uri = exchange.getRequest().getURI();

		// if the `lb:` mechanism was used, use `` as the default,
		// if the loadbalancer doesn't provide one.
		String overrideScheme = instance.isSecure() ? "https" : "http";
		if (schemePrefix != null) {
			overrideScheme = url.getScheme();
		}
		// 选择好节点以后重新组织请求URI
		URI requestUrl = loadBalancer.reconstructURI(
				new DelegatingServiceInstance(instance, overrideScheme), uri);

		if (log.isTraceEnabled()) {
			log.trace("LoadBalancerClientFilter url chosen: " + requestUrl);
		}

		exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, requestUrl);
		return chain.filter(exchange);
	}

自定义拦截

首先看官方网提供的几种断言，都是比较简单的这里不在演示：
官网地址
源码，这些类提供了这些能力：

自定义局部
自定义类，这个类可以参考DedupeResponseHeaderGatewayFilterFactory进行定义

@Component
public class CostGatewayFilterFactory extends
        AbstractGatewayFilterFactory<CostGatewayFilterFactory.CustomConfig> {
    public CostGatewayFilterFactory() {
        super(CustomConfig.class);
    }
    @Override
    public List<String> shortcutFieldOrder() {
       return Arrays.asList("switchStatus");
    }
    @Override
    public GatewayFilter apply(CostGatewayFilterFactory.CustomConfig config) {
        return new GatewayFilter() {

            @Override
            public Mono<Void> filter(ServerWebExchange exchange,
                                     GatewayFilterChain chain) {
                if (!config.switchStatus.equalsIgnoreCase("on")) {
                    // 如果这个开关是关闭状态
                   return chain.filter(exchange);
                }
                long sTime = System.currentTimeMillis();
                exchange.getAttributes().put("STIME", sTime);
                return chain.filter(exchange).then(Mono.fromRunnable(
                        () -> {
                            long stime = (long) exchange.getAttributes().get("STIME");
                            long cost = System.currentTimeMillis() - stime;
                            System.out.println("cost is : " + cost + " ms");
                        }));
            }
            @Override
            public String toString() {
                return filterToStringCreator(
                        CostGatewayFilterFactory.this)
                        .append(config.getSwitchStatus(), config.getSwitchStatus())
                        .toString();
            }
        };
    }
    public static class CustomConfig  {
        private String switchStatus;

        public String getSwitchStatus() {
            return switchStatus;
        }

        public void setSwitchStatus(String switchStatus) {
            this.switchStatus = switchStatus;
        }
    }
}

配置

routes:
  - id: gateway-provider
    uri: http://127.0.0.1:8088
    predicates:
      - Path=/provider/**
    filters:
      - StripPrefix=1
      - Cost=ON # 这个名字取前面GatewayFilterFactory的

自定义全局

@Component
public class GlobalCustomFilter implements GlobalFilter {
    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        // 过滤前
        System.out.println("Before : " + exchange.getRequest().getURI());
        return chain.filter(exchange).then(Mono.fromRunnable(
                () -> {
                    long stime = (long) exchange.getAttributes().get("STIME");
                    long cost = System.currentTimeMillis() - stime;
                    System.out.println("End cost time is  : " +  cost);
                }));
    }
}

Spring Cloud Gateway 是基于Netty 实现的，而不是Tomcat。我本来想试试mvc的过滤器和gateway的过滤器的优先级，结果怎么配置filter也不生效，原来如此，菜狗终究是菜狗。
可以换为Tomcat

转发重定向原理

• Gateway 框架体系处理的入口org.springframework.http.server.reactive.ReactorHttpHandlerAdapter
• 构建网关上下文：org.springframework.web.server.adapter.HttpWebHandlerAdapter
• 遍历 Mapping 获取真实处理请求的 Handler org.springframework.web.reactive.DispatcherHandler
• 构建过滤器链：org.springframework.cloud.gateway.handler.FilteringWebHandler
• 过滤器必经之路：org.springframework.cloud.gateway.handler.FilteringWebHandler.DefaultGatewayFilterChain
• 负载均衡过滤器：org.springframework.cloud.gateway.filter.LoadBalancerClientFilter
• 利用 Netty 发送网络请求过滤器：org.springframework.cloud.gateway.filter.NettyRoutingFilter
  
  RouteToRequestUrlFilter 这个过滤器处理了Route的配置，并且将请求的真实地址存放到了

URI mergedUrl = UriComponentsBuilder.fromUri(uri)
		// .uri(routeUri)
		.scheme(routeUri.getScheme()).host(routeUri.getHost())
		.port(routeUri.getPort()).build(encoded).toUri();
exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, mergedUrl);

NettyRoutingFilter 进行了真正的转发调用

这个经典的图必须贴上：