问题

Spring Cloud Gateway版本是2.2.9.RELEASE，原本项目中依赖服务自动发现来自动配置路由到微服务的，但是发现将spring.cloud.gateway.discovery.locator.enabled=false 启动之后Gateway依然会将所有微服务自动注册到路由中，百思不得其解，遂调试代码观察期启动过曾，记录此文以供参考，官方文档

可以看到此处明确表示，可以通过设置该值来讲微服务中服务自动添加到配置中。按照这个线索，找到了
org.springframework.cloud.gateway.discovery.DiscoveryClientRouteDefinitionLocator#getRouteDefinitions
这个类在之前的文章includeExpression中有提及过，在构造函数中对成员变量

public class DiscoveryClientRouteDefinitionLocator implements RouteDefinitionLocator {

	private final DiscoveryLocatorProperties properties;
	...
	private Flux<List<ServiceInstance>> serviceInstances;

	/**
	 * Kept for backwards compatibility. You should use the reactive discovery client.
	 * @param discoveryClient the blocking discovery client
	 * @param properties the configuration properties
	 * @deprecated kept for backwards compatibility
	 */
	@Deprecated
	public DiscoveryClientRouteDefinitionLocator(DiscoveryClient discoveryClient,
			DiscoveryLocatorProperties properties) {
		this(discoveryClient.getClass().getSimpleName(), properties);
		serviceInstances = Flux
				.defer(() -> Flux.fromIterable(discoveryClient.getServices()))
				.map(discoveryClient::getInstances)
				.subscribeOn(Schedulers.boundedElastic());
	}

	public DiscoveryClientRouteDefinitionLocator(ReactiveDiscoveryClient discoveryClient,
			DiscoveryLocatorProperties properties) {
		this(discoveryClient.getClass().getSimpleName(), properties);
		serviceInstances = discoveryClient.getServices()
				.flatMap(service -> discoveryClient.getInstances(service).collectList());
	}
	...

这里会对serviceInstances进行初始化，从注册中心获取所有已注册的微服务实例进行填充，serviceInstance的获取结束了,在DiscoveryClientRouteDefinitionLocator还有一个重要的方法

#DiscoveryClientRouteDefinitionLocator
	@Override
	public Flux<RouteDefinition> getRouteDefinitions() {

		SpelExpressionParser parser = new SpelExpressionParser();
		Expression includeExpr = parser
				.parseExpression(properties.getIncludeExpression());
		Expression urlExpr = parser.parseExpression(properties.getUrlExpression());

		Predicate<ServiceInstance> includePredicate;
		if (properties.getIncludeExpression() == null
				|| "true".equalsIgnoreCase(properties.getIncludeExpression())) {
			includePredicate = instance -> true;
		}
		else {
			includePredicate = instance -> {
				Boolean include = includeExpr.getValue(evalCtxt, instance, Boolean.class);
				if (include == null) {
					return false;
				}
				return include;
			};
		}

		return serviceInstances.filter(instances -> !instances.isEmpty())
				.map(instances -> instances.get(0)).filter(includePredicate)
				.map(instance -> {
					RouteDefinition routeDefinition = buildRouteDefinition(urlExpr,
							instance);

					final ServiceInstance instanceForEval = new DelegatingServiceInstance(
							instance, properties);

					for (PredicateDefinition original : this.properties.getPredicates()) {
						PredicateDefinition predicate = new PredicateDefinition();
						predicate.setName(original.getName());
						for (Map.Entry<String, String> entry : original.getArgs()
								.entrySet()) {
							String value = getValueFromExpr(evalCtxt, parser,
									instanceForEval, entry);
							predicate.addArg(entry.getKey(), value);
						}
						routeDefinition.getPredicates().add(predicate);
					}

					for (FilterDefinition original : this.properties.getFilters()) {
						FilterDefinition filter = new FilterDefinition();
						filter.setName(original.getName());
						for (Map.Entry<String, String> entry : original.getArgs()
								.entrySet()) {
							String value = getValueFromExpr(evalCtxt, parser,
									instanceForEval, entry);
							filter.addArg(entry.getKey(), value);
						}
						routeDefinition.getFilters().add(filter);
					}

					return routeDefinition;
				});
	}

根据includeExpr 配置的sl表达式判断当前的serviceInstance是否服务转发要求。填充好predicate，filter之后返回routeDefinition，urlExpr的默认值是"lb://"+serverId，predicate匹配的path就等于serverId，有配置可以转换为小写spring.cloud.gateway.discovery.locator.lower-case-service-id=true因为eureka默认会uppercase serverId，filter中会StripPrefix=1，将路径中的serverId移除再转发给下游。路由定义的部分就这里了，他的刷新逻辑，依靠SpringRefreshContext 事件，具体的定义逻辑在org.springframework.cloud.gateway.config.GatewayAutoConfiguration

	@Bean
	@ConditionalOnClass(
			name = "org.springframework.cloud.client.discovery.event.HeartbeatMonitor")
	public RouteRefreshListener routeRefreshListener(
			ApplicationEventPublisher publisher) {
		return new RouteRefreshListener(publisher);
	}

RouteRefreshListener 实现了ApplicationListener<ApplicationEvent>，监控以下几个事件，并按照条件进行逻辑执行

• ContextRefreshEvent 启动容器，或者beans重新加载
• RefreshScopeRefreshdEvent 是 Spring Cloud 中的一个事件，当 @RefreshScope 注解的 beans 被重新加载时发布。这个事件主要用于 Spring Cloud 的配置刷新机制，当配置中心的配置信息发生变化时，会触发该事件以刷新 beans。
• ParentHeartbeatEvent 是 Spring Cloud Bus 中的一个事件，用于在父上下文（通常是 Spring Cloud Config Server）发生心跳时发布。这个事件用于通知子上下文（如微服务）关于父上下文的健康状态。
• HeartbeatEvent 是 Spring Cloud Bus 中的另一个事件，用于在服务实例之间广播心跳消息，以检测和维持各个服务的健康状态。

	public void onApplicationEvent(ApplicationEvent event) {
		if (event instanceof ContextRefreshedEvent) {
			ContextRefreshedEvent refreshedEvent = (ContextRefreshedEvent) event;
			if (!WebServerApplicationContext.hasServerNamespace(
					refreshedEvent.getApplicationContext(), "management")) {
				reset();
			}
		}
		else if (event instanceof RefreshScopeRefreshedEvent
				|| event instanceof InstanceRegisteredEvent) {
			reset();
		}
		else if (event instanceof ParentHeartbeatEvent) {
			ParentHeartbeatEvent e = (ParentHeartbeatEvent) event;
			resetIfNeeded(e.getValue());
		}
		else if (event instanceof HeartbeatEvent) {
			HeartbeatEvent e = (HeartbeatEvent) event;
			resetIfNeeded(e.getValue());
		}
	}

容器启动完成之后，该监听器接收到ContextRefreshedEvent ，会执行reset方法，reset方法主要功能是发送一个RefreshRoutesEvent 事件，定义如下

public class RefreshRoutesEvent extends ApplicationEvent {
	public RefreshRoutesEvent(Object source) {
		super(source);
	}
}

同样在AutoConfig中声明的CachingRouteLocator接收该参数，

tip:另外还有个CachingRouteDefinitionLocator也生命监听 RefreshRoutesEvent事件，但是默认配置下并不会产生任何逻辑

	@Bean
	@Primary
	@ConditionalOnMissingBean(name = "cachedCompositeRouteLocator")
	// TODO: property to disable composite?
	public RouteLocator cachedCompositeRouteLocator(List<RouteLocator> routeLocators) {
		return new CachingRouteLocator(
				new CompositeRouteLocator(Flux.fromIterable(routeLocators)));
	}

event invoke方法如下

	public void onApplicationEvent(RefreshRoutesEvent event) {
		try {
			fetch().collect(Collectors.toList()).subscribe(list -> Flux.fromIterable(list)
					.materialize().collect(Collectors.toList()).subscribe(signals -> {
						applicationEventPublisher
								.publishEvent(new RefreshRoutesResultEvent(this));
						cache.put(CACHE_KEY, signals);
					}, throwable -> handleRefreshError(throwable)));
		}
		catch (Throwable e) {
			handleRefreshError(e);
		}
	}

CompositeRouteLocator的目的是混合 多个来源的Routers定义比如配置文件，接口，注册中心，通过@Bean形式定义的路由。可以理解成mixed route locator。
fetch方法就是获取所有RouteLocator的路由定义
private Flux<Route> fetch() { return this.delegate.getRoutes().sort(AnnotationAwareOrderComparator.INSTANCE); }
这里其实就是指定，之前org.springframework.cloud.gateway.discovery.DiscoveryClientRouteDefinitionLocator#getRouteDefinitions的方法也就是获取具体的路由定义，获取成功之后放入缓存，Fire RefreshRoutesResultEvent事件就解决了，开发人员可以通过 监听RefreshRoutesResultEvent 主动感知当前的路由变化。路由加载流程到此结束，

后语

我的问题是通过设置spring.cloud.gateway.discovery.locator.enabled依然没有办法让微服务注册失效，在整个流程中并没有看到使用该数值的地方，难道这是一个bug？转念一想DiscoveryClientRouteDefinitionLocator只需要阻止该Bean的注册即可取消掉从eureka获取服务实例的能力，通过引用关系可知

• org.springframework.cloud.gateway.discovery.GatewayDiscoveryClientAutoConfiguration.ReactiveDiscoveryClientRouteDefinitionLocatorConfiguration
• org.springframework.cloud.gateway.discovery.GatewayDiscoveryClientAutoConfiguration.BlockingDiscoveryClientRouteDefinitionLocatorConfiguration

这里两处找到了其定义，一个是为reactive非阻塞io准备的，一个是为阻塞io准备的，根据源代码可知,具体执行提供那个Locator取决于spring.cloud.discovery.reactive.enabled，我的项目中是通过VM Options参数的形式传入的-Dspring.cloud.config.discovery.enabled=true，所以我在这两个方法处都打了断点。

		@Configuration(proxyBeanMethods = false)
	@ConditionalOnProperty(value = "spring.cloud.discovery.reactive.enabled",
			matchIfMissing = true)
	public static class ReactiveDiscoveryClientRouteDefinitionLocatorConfiguration {

		@Bean
		@ConditionalOnProperty(name = "spring.cloud.gateway.discovery.locator.enabled")
		public DiscoveryClientRouteDefinitionLocator discoveryClientRouteDefinitionLocator(
				ReactiveDiscoveryClient discoveryClient,
				DiscoveryLocatorProperties properties) {
			return new DiscoveryClientRouteDefinitionLocator(discoveryClient, properties);
		}

	}

	@Configuration(proxyBeanMethods = false)
	@Deprecated
	@ConditionalOnProperty(value = "spring.cloud.discovery.reactive.enabled",
			havingValue = "false")
	public static class BlockingDiscoveryClientRouteDefinitionLocatorConfiguration {

		@Bean
		@ConditionalOnProperty(name = "spring.cloud.gateway.discovery.locator.enabled")
		public DiscoveryClientRouteDefinitionLocator discoveryClientRouteDefinitionLocator(
				DiscoveryClient discoveryClient, DiscoveryLocatorProperties properties) {
			return new DiscoveryClientRouteDefinitionLocator(discoveryClient, properties);
		}

	}

当我准备要执行调试模式想看看具体是哪个Bean被初始化的时候，恍然大悟看到了DiscoveryClientRouteDefinitionLocator的依赖，我自己在GatewayApplication 中手动注册了Bean

    @Bean
    public DiscoveryClientRouteDefinitionLocator discoveryClientRouteLocator(ReactiveDiscoveryClient discoveryClient,
            DiscoveryLocatorProperties discoveryLocatorProperties) {
        return new DiscoveryClientRouteDefinitionLocator(discoveryClient, discoveryLocatorProperties);
    }

真的是笑死，出这个问题的原因是因为最开始的代码使用的出c4o老师生成的，一开始并不明确该代码的作用，后面查看文档才知道用于微服务发现。已经不在关注这里了。