SpringCloud Ribbon（五）之服务实例列表ServerList

Myth丶恋晨 2022-10-29 14:23 179阅读 0赞

### 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 ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L21vYWt1bg_size_16_color_FFFFFF_t_70][]

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;
    	}
    
    	@Override
    	public List<NacosServer> getInitialListOfServers() {
    		return getServers();
    	}
    
    	@Override
    	public 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;
    	}
    
    	@Override
    	public void initWithNiwsConfig(IClientConfig iClientConfig) {
    		this.serviceId = iClientConfig.getClientName();
    	}
    }

（2）ConfigurationBasedServerList

public class ConfigurationBasedServerList extends AbstractServerList<Server>  {
    
    	private IClientConfig clientConfig;
    		
    	@Override
    	public List<Server> getInitialListOfServers() {
    	    return getUpdatedListOfServers();
    	}
    
    	@Override
    	public List<Server> getUpdatedListOfServers() {
            String listOfServers = clientConfig.get(CommonClientConfigKey.ListOfServers);
            return derive(listOfServers);
    	}
    
    	@Override
    	public 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);
    	}
    
    	@Override
    	public List<T> getInitialListOfServers() {
    		return servers;
    	}
    
    	@Override
    	public List<T> getUpdatedListOfServers() {
    		return servers;
    	}
    
    }

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