nacos配置中心源码分析（1）

nacos版本

 <dependency>
     <groupId>com.alibaba.cloud</groupId>
     <artifactId>spring-cloud-starter-alibaba-nacos-config</artifactId>
     <version>2.0.0.RELEASE</version>
 </dependency>

bootstrap.yaml

spring:
  application:
    name: service1
  profiles:
    active: dev
  cloud:
    nacos:
      config:
        namespace: 14d29622-bf23-4d4a-b86d-cdedc18ff83b
        file-extension: yaml
        server-addr: 127.0.0.1:8848
        ext-config[0]:
          data-id: common-${spring.profiles.active}.yaml
          refresh: true

nacos是Alibaba 开源的微服务发现、管理、配置的组件，它提供了server端和客户端的能力，这里我们将来分析下nacos与spring cloud服务集成，作为微服务的配置中心的nacos的底层源码

nacos读取配置分析

// springboot服务的统一入口
public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
}

启动微服务，从SpringApplication.run()方法进入，到达SpringApplication#run(java.lang.String...) 进行spring容器的启动的各项工作：
1、准备上下文

2、应用初始化设定（配置刷新）

3、加载各种初始化配置，其中包括属性配置初始化

4、PropertySourceBootstrapConfiguration#initialize方法中加载到nacos配置源

public void initialize(ConfigurableApplicationContext applicationContext) {
   List<PropertySource<?>> composite = new ArrayList<>();
   AnnotationAwareOrderComparator.sort(this.propertySourceLocators);
   boolean empty = true;
   ConfigurableEnvironment environment = applicationContext.getEnvironment();
   for (PropertySourceLocator locator : this.propertySourceLocators) {
       // 配置源
      Collection<PropertySource<?>> source = locator.locateCollection(environment);
      if (source == null || source.size() == 0) {
         continue;
      }
      List<PropertySource<?>> sourceList = new ArrayList<>();
      for (PropertySource<?> p : source) {
         if (p instanceof EnumerablePropertySource) {
            EnumerablePropertySource<?> enumerable = (EnumerablePropertySource<?>) p;
            sourceList.add(new BootstrapPropertySource<>(enumerable));
         }
         else {
            sourceList.add(new SimpleBootstrapPropertySource(p));
         }
      }
      logger.info("Located property source: " + sourceList);
      composite.addAll(sourceList);
      empty = false;
   }
   if (!empty) {
      MutablePropertySources propertySources = environment.getPropertySources();
      String logConfig = environment.resolvePlaceholders("${logging.config:}");
      LogFile logFile = LogFile.get(environment);
      for (PropertySource<?> p : environment.getPropertySources()) {
         if (p.getName().startsWith(BOOTSTRAP_PROPERTY_SOURCE_NAME)) {
            propertySources.remove(p.getName());
         }
      }
      insertPropertySources(propertySources, composite);
      reinitializeLoggingSystem(environment, logConfig, logFile);
      setLogLevels(applicationContext, environment);
      handleIncludedProfiles(environment);
   }
}

5、然后到达此方法NacosPropertySourceLocator#locate 进行bootstrap.yaml配置的nacos相关配置获取与加载

public PropertySource<?> locate(Environment env) {

   ConfigService configService = nacosConfigProperties.configServiceInstance();

   if (null == configService) {
      log.warn("no instance of config service found, can't load config from nacos");
      return null;
   }
   long timeout = nacosConfigProperties.getTimeout();
   nacosPropertySourceBuilder = new NacosPropertySourceBuilder(configService,
         timeout);
   String name = nacosConfigProperties.getName();

   String dataIdPrefix = nacosConfigProperties.getPrefix();
   if (StringUtils.isEmpty(dataIdPrefix)) {
      dataIdPrefix = name;
   }

   if (StringUtils.isEmpty(dataIdPrefix)) {
      dataIdPrefix = env.getProperty("spring.application.name");
   }

   CompositePropertySource composite = new CompositePropertySource(
         NACOS_PROPERTY_SOURCE_NAME);
    // 加载共享配置 对应 shared-dataids 配置项
   loadSharedConfiguration(composite);
    // 加载额外配置 对应 ext-config[n] 配置项
   loadExtConfiguration(composite);
    // 加载微服务对应配置
   loadApplicationConfiguration(composite, dataIdPrefix, nacosConfigProperties, env);

   return composite;
}

6、主要看NacosPropertySourceLocator#loadApplicationConfiguration 加载微服务配置，另外两个加载方法雷同。加载顺序，按照

${prefix}.${file-extension}  => ${prefix}-${spring.profiles.active}.${file-extension} 

7、第一次启动从远程获取数据进行加载

8、然后在NacosConfigService#getConfigInner方法进行加载配置，首先加载本地配置：nacos从远程读取配置文件成功，会将配置文件快照备份在磁盘上，当无法连接服务端时，使用本地快照的配置。如果存在本地备份，则不会从远程获取配置。那如果配置发生更新怎么办？这就涉及到nacos动态配置功能，将在下一篇进行分析。

private String getConfigInner(String tenant, String dataId, String group, long timeoutMs) throws NacosException {
    group = null2defaultGroup(group);
    ParamUtils.checkKeyParam(dataId, group);
    ConfigResponse cr = new ConfigResponse();

    cr.setDataId(dataId);
    cr.setTenant(tenant);
    cr.setGroup(group);

    // 优先使用本地配置
    String content = LocalConfigInfoProcessor.getFailover(agent.getName(), dataId, group, tenant);
    if (content != null) {
        LOGGER.warn("[{}] [get-config] get failover ok, dataId={}, group={}, tenant={}, config={}", agent.getName(),
            dataId, group, tenant, ContentUtils.truncateContent(content));
        cr.setContent(content);
        configFilterChainManager.doFilter(null, cr);
        content = cr.getContent();
        return content;
    }

    try {  // 没有磁盘快照，从配置中心加载服务配置
        content = worker.getServerConfig(dataId, group, tenant, timeoutMs);

        cr.setContent(content);

        configFilterChainManager.doFilter(null, cr);
        content = cr.getContent();

        return content;
    } catch (NacosException ioe) {
        if (NacosException.NO_RIGHT == ioe.getErrCode()) {
            throw ioe;
        }
        LOGGER.warn("[{}] [get-config] get from server error, dataId={}, group={}, tenant={}, msg={}",
            agent.getName(), dataId, group, tenant, ioe.toString());
    }

    LOGGER.warn("[{}] [get-config] get snapshot ok, dataId={}, group={}, tenant={}, config={}", agent.getName(),
        dataId, group, tenant, ContentUtils.truncateContent(content));
    content = LocalConfigInfoProcessor.getSnapshot(agent.getName(), dataId, group, tenant);
    cr.setContent(content);
    configFilterChainManager.doFilter(null, cr);
    content = cr.getContent();
    return content;
}

9、ClientWorker#getServerConfig方法

public String getServerConfig(String dataId, String group, String tenant, long readTimeout)
    throws NacosException {
    if (StringUtils.isBlank(group)) {
        group = Constants.DEFAULT_GROUP;
    }

    HttpResult result = null;
    try {
        List<String> params = null;
        if (StringUtils.isBlank(tenant)) {
            params = Arrays.asList("dataId", dataId, "group", group);
        } else {
            params = Arrays.asList("dataId", dataId, "group", group, "tenant", tenant);
        }
        // get方法获取配置文件内容
        result = agent.httpGet(Constants.CONFIG_CONTROLLER_PATH, null, params, agent.getEncode(), readTimeout);
    } catch (IOException e) {
        String message = String.format(
            "[%s] [sub-server] get server config exception, dataId=%s, group=%s, tenant=%s", agent.getName(),
            dataId, group, tenant);
        LOGGER.error(message, e);
        throw new NacosException(NacosException.SERVER_ERROR, e);
    }

    switch (result.code) {
        case HttpURLConnection.HTTP_OK:
            // 备份快照至磁盘
            LocalConfigInfoProcessor.saveSnapshot(agent.getName(), dataId, group, tenant, result.content);
            return result.content;
        case HttpURLConnection.HTTP_NOT_FOUND:
            LocalConfigInfoProcessor.saveSnapshot(agent.getName(), dataId, group, tenant, null);
            return null;
        case HttpURLConnection.HTTP_CONFLICT: {
            LOGGER.error(
                "[{}] [sub-server-error] get server config being modified concurrently, dataId={}, group={}, "
                    + "tenant={}", agent.getName(), dataId, group, tenant);
            throw new NacosException(NacosException.CONFLICT,
                "data being modified, dataId=" + dataId + ",group=" + group + ",tenant=" + tenant);
        }
        case HttpURLConnection.HTTP_FORBIDDEN: {
            LOGGER.error("[{}] [sub-server-error] no right, dataId={}, group={}, tenant={}", agent.getName(), dataId,
                group, tenant);
            throw new NacosException(result.code, result.content);
        }
        default: {
            LOGGER.error("[{}] [sub-server-error]  dataId={}, group={}, tenant={}, code={}", agent.getName(), dataId,
                group, tenant, result.code);
            throw new NacosException(result.code,
                "http error, code=" + result.code + ",dataId=" + dataId + ",group=" + group + ",tenant=" + tenant);
        }
    }
}

10、具体http请求方法，请求失败时，重试3次，从服务端配置地址获取下一个服务地址进行新的请求。如果请求成功nacos服务端返回的字符串内容。

public HttpResult httpGet(String path, List<String> headers, List<String> paramValues, String encoding,
                          long readTimeoutMs) throws IOException {
    final long endTime = System.currentTimeMillis() + readTimeoutMs;
    final boolean isSSL = false;

    String currentServerAddr = serverListMgr.getCurrentServerAddr();
    // 默认 3
    int maxRetry = this.maxRetry;

    do {
        try {
            List<String> newHeaders = getSpasHeaders(paramValues);
            if (headers != null) {
                newHeaders.addAll(headers);
            }
            HttpResult result = HttpSimpleClient.httpGet(
                getUrl(currentServerAddr, path), newHeaders, paramValues, encoding,
                readTimeoutMs, isSSL);
            if (result.code == HttpURLConnection.HTTP_INTERNAL_ERROR
                || result.code == HttpURLConnection.HTTP_BAD_GATEWAY
                || result.code == HttpURLConnection.HTTP_UNAVAILABLE) {
                LOGGER.error("[NACOS ConnectException] currentServerAddr: {}, httpCode: {}",
                    serverListMgr.getCurrentServerAddr(), result.code);
            } else {
                // Update the currently available server addr
                serverListMgr.updateCurrentServerAddr(currentServerAddr);
                return result;
            }
        } catch (ConnectException ce) {
            LOGGER.error("[NACOS ConnectException httpGet] currentServerAddr:{}, err : {}", serverListMgr.getCurrentServerAddr(), ce.getMessage());
        } catch (SocketTimeoutException stoe) {
            LOGGER.error("[NACOS SocketTimeoutException httpGet] currentServerAddr:{}， err : {}", serverListMgr.getCurrentServerAddr(), stoe.getMessage());
        } catch (IOException ioe) {
            LOGGER.error("[NACOS IOException httpGet] currentServerAddr: " + serverListMgr.getCurrentServerAddr(), ioe);
            throw ioe;
        }

        if (serverListMgr.getIterator().hasNext()) {
            // 下一个nacos服务地址
            currentServerAddr = serverListMgr.getIterator().next();
        } else {
            maxRetry --;
            if (maxRetry < 0) {
                throw new ConnectException("[NACOS HTTP-GET] The maximum number of tolerable server reconnection errors has been reached");
            }
            serverListMgr.refreshCurrentServerAddr();
        }

    } while (System.currentTimeMillis() <= endTime);

    LOGGER.error("no available server");
    throw new ConnectException("no available server");
}

至此，nacos从配置中心加载配置的源码就分析完了。