SpringCloud Gateway+DiscoveryClient实现自动路由源码

1. 服务发现自动配置
   org.springframework.cloud.gateway.discovery.GatewayDiscoveryClientAutoConfiguration

@Configuration(proxyBeanMethods = false)
@ConditionalOnProperty(name = "spring.cloud.gateway.enabled", matchIfMissing = true)
@AutoConfigureBefore(GatewayAutoConfiguration.class)
@AutoConfigureAfter(CompositeDiscoveryClientAutoConfiguration.class)
@ConditionalOnClass({ DispatcherHandler.class, CompositeDiscoveryClientAutoConfiguration.class })
@EnableConfigurationProperties
public class GatewayDiscoveryClientAutoConfiguration {
	...
	@Configuration(proxyBeanMethods = false)
	@ConditionalOnProperty(value = "spring.cloud.discovery.reactive.enabled", matchIfMissing = true)
	public static class ReactiveDiscoveryClientRouteDefinitionLocatorConfiguration {
		// 根据配置启用服务发现定位器
		@Bean
		@ConditionalOnProperty(name = "spring.cloud.gateway.discovery.locator.enabled")
		public DiscoveryClientRouteDefinitionLocator discoveryClientRouteDefinitionLocator(
				ReactiveDiscoveryClient discoveryClient, DiscoveryLocatorProperties properties) {
			return new DiscoveryClientRouteDefinitionLocator(discoveryClient, properties);
		}

	}
}

2. 服务发现定位器
   org.springframework.cloud.gateway.discovery.DiscoveryClientRouteDefinitionLocator

public class DiscoveryClientRouteDefinitionLocator implements RouteDefinitionLocator {
	...
	// 服务实例
	private Flux<List<ServiceInstance>> serviceInstances;
	public DiscoveryClientRouteDefinitionLocator(ReactiveDiscoveryClient discoveryClient,
			DiscoveryLocatorProperties properties) {
		this(discoveryClient.getClass().getSimpleName(), properties);
		serviceInstances = discoveryClient.getServices()
				.flatMap(service -> discoveryClient.getInstances(service).collectList());
	}
	...
	// 根据服务实例动态获取路由定义
	@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;
				});
	}
}