springcloud-gateway 路由加载流程

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
在这里插入图片描述
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*/@Deprecatedpublic 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@Overridepublic 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

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