1. 概述
本文主要对 DiscoveryClientRouteDefinitionLocator 的源码实现。
DiscoveryClientRouteDefinitionLocator 通过调用 org.springframework.cloud.client.discovery.DiscoveryClient 获取注册在注册中心的服务列表，生成对应的 RouteDefinition 数组。
2. 环境搭建
在解析源码之前，我们先以 Eureka 为注册中心，讲解下如何配置 DiscoveryClientRouteDefinitionLocator 。
第一步，以 spring-cloud-gateway-sample 项目为基础，在 pom.xml 文件添加依赖库。
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-commons</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-eureka</artifactId>
<version>2.0.0.M1</version>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</exclusion>
</exclusions>
</dependency>
- 注意，需要排除
spring-boot-starter-web 的依赖，避免和 Spring Cloud Gateway 依赖的 spring-boot-starter-webflux 冲突。
第二步，在 application.yml 添加 Eureka 相关配置 。
spring:
application:
name: juejin-gateway
eureka:
instance:
leaseRenewalIntervalInSeconds: 10
leaseExpirationDurationInSeconds: 30
client:
serviceUrl:
defaultZone: http://eureka.didispace.com/eureka/
第三步，在 org.springframework.cloud.gateway.sample.GatewaySampleApplication 类里，添加 RouteDefinitionLocator Bean 配置
@EnableDiscoveryClient // {@link DiscoveryClientRouteDefinitionLocator}
public class GatewaySampleApplication {
// ... 省略其他代码
@Bean
public RouteDefinitionLocator discoveryClientRouteDefinitionLocator(DiscoveryClient discoveryClient) {
return new DiscoveryClientRouteDefinitionLocator(discoveryClient);
}
}
第四步，启动一个注册在 Eureka 的应用服务。机智如你，这里我就不啰嗦落。
第五步，在 DiscoveryClientRouteDefinitionLocator 的 #getRouteDefinitions() 方法打断点，调试启动 spring-cloud-gateway-sample 。小功告成。撒花~
3. DiscoveryClientRouteDefinitionLocator
org.springframework.cloud.gateway.discovery.DiscoveryClientRouteDefinitionLocator ，通过调用 DiscoveryClient 获取注册在注册中心的服务列表，生成对应的 RouteDefinition 数组。
代码如下 ：
1: public class DiscoveryClientRouteDefinitionLocator implements RouteDefinitionLocator {
2:
3: private final DiscoveryClient discoveryClient;
4: private final String routeIdPrefix;
5:
6: public DiscoveryClientRouteDefinitionLocator(DiscoveryClient discoveryClient) {
7: this.discoveryClient = discoveryClient;
8: this.routeIdPrefix = this.discoveryClient.getClass().getSimpleName() + "_";
9: }
10:
11: @Override
12: public Flux<RouteDefinition> getRouteDefinitions() {
13: return Flux.fromIterable(discoveryClient.getServices())
14: .map(serviceId -> {
15: RouteDefinition routeDefinition = new RouteDefinition();
16: // 设置 ID
17: routeDefinition.setId(this.routeIdPrefix + serviceId);
18: // 设置 URI
19: routeDefinition.setUri(URI.create("lb://" + serviceId));
20:
21: // add a predicate that matches the url at /serviceId
22: /*PredicateDefinition barePredicate = new PredicateDefinition();
23: barePredicate.setName(normalizePredicateName(PathRoutePredicateFactory.class));
24: barePredicate.addArg(PATTERN_KEY, "/" + serviceId);
25: routeDefinition.getPredicates().add(barePredicate);*/
26:
27: // 添加 Path 匹配断言
28: // add a predicate that matches the url at /serviceId/**
29: PredicateDefinition subPredicate = new PredicateDefinition();
30: subPredicate.setName(normalizePredicateName(PathRoutePredicateFactory.class));
31: subPredicate.addArg(PATTERN_KEY, "/" + serviceId + "/**");
32: routeDefinition.getPredicates().add(subPredicate);
33:
34: //TODO: support for other default predicates
35:
36: // 添加 Path 重写过滤器
37: // add a filter that removes /serviceId by default
38: FilterDefinition filter = new FilterDefinition();
39: filter.setName(normalizeFilterName(RewritePathGatewayFilterFactory.class));
40: String regex = "/" + serviceId + "/(?<remaining>.*)";
41: String replacement = "/${remaining}";
42: filter.addArg(REGEXP_KEY, regex);
43: filter.addArg(REPLACEMENT_KEY, replacement);
44: routeDefinition.getFilters().add(filter);
45:
46: //TODO: support for default filters
47:
48: return routeDefinition;
49: });
50: }
51: }
4. 高能
本小节建议阅读完 《Spring-Cloud-Gateway 源码解析 —— 路由（2.1）之 RouteLocator 一览》 再理解。
RoutePredicateHandlerMapping 使用 CachingRouteLocator 来获取 Route 信息。在 Spring Cloud Gateway 启动后，如果有新加入的服务，则需要刷新 CachingRouteLocator 缓存。
这里有一点需要注意下 ：新加入的服务，指的是新的 serviceId ，而不是原有服务新增的实例。
个人建议，写一个定时任务，间隔调用 DiscoveryClient 获取服务列表，若发现变化，刷新 CachingRouteLocator 缓存。
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