一、服务实例列表ServerList

服务实例列表（ServerList）为负载均衡器（Loadbalancer）提供服务的可用实例列表。

负载均衡器（Loadbalancer）通过服务实例列表（ServerList）从注册中心（register）或者配置文件（yaml或properties）上读取全部服务实例（server），然后以服务实例过滤器（ServerListFilter）的过滤方式进行筛选留下满足条件的服务实例，进而借助负载均衡策略（IRule）选择出一个合适的服务实例。

 

二、ServerList实现类

NacosServerList   nacos服务发现提供的ServerList

ConfigurationBasedServerList   从配置文件读取静态的服务实例定义

StaticServerList  静态ServerList创建包含不变的服务实例（server）

 

三、具体代码实现

（1）NacosServerList   

public class NacosServerList extends AbstractServerList<NacosServer> {private NacosDiscoveryProperties discoveryProperties;private String serviceId;public NacosServerList(NacosDiscoveryProperties discoveryProperties) {this.discoveryProperties = discoveryProperties;}@Overridepublic List<NacosServer> getInitialListOfServers() {return getServers();}@Overridepublic List<NacosServer> getUpdatedListOfServers() {return getServers();}private List<NacosServer> getServers() {try {List<Instance> instances = discoveryProperties.namingServiceInstance().selectInstances(serviceId, true);return instancesToServerList(instances);}catch (Exception e) {throw new IllegalStateException("Can not get service instances from nacos, serviceId=" + serviceId,e);}}private List<NacosServer> instancesToServerList(List<Instance> instances) {List<NacosServer> result = new ArrayList<>();if (null == instances) {return result;}for (Instance instance : instances) {result.add(new NacosServer(instance));}return result;}public String getServiceId() {return serviceId;}@Overridepublic void initWithNiwsConfig(IClientConfig iClientConfig) {this.serviceId = iClientConfig.getClientName();}
}

（2）ConfigurationBasedServerList 

public class ConfigurationBasedServerList extends AbstractServerList<Server>  {private IClientConfig clientConfig;@Overridepublic List<Server> getInitialListOfServers() {return getUpdatedListOfServers();}@Overridepublic List<Server> getUpdatedListOfServers() {String listOfServers = clientConfig.get(CommonClientConfigKey.ListOfServers);return derive(listOfServers);}@Overridepublic void initWithNiwsConfig(IClientConfig clientConfig) {this.clientConfig = clientConfig;}protected List<Server> derive(String value) {List<Server> list = Lists.newArrayList();if (!Strings.isNullOrEmpty(value)) {for (String s: value.split(",")) {list.add(new Server(s.trim()));}}return list;}
}

（3）StaticServerList 

public class StaticServerList<T extends Server> implements ServerList<T> {private final List<T> servers;public StaticServerList(T... servers) {this.servers = Arrays.asList(servers);}@Overridepublic List<T> getInitialListOfServers() {return servers;}@Overridepublic List<T> getUpdatedListOfServers() {return servers;}}