1、加載節點

SpringBoot啟動時，會執行這個方法：SpringApplication#run，這個方法中會調prepareContext來準備上下文，這個方法中調用了applyInitializers方法來執行實現了ApplicationContextInitializer接口的類的initialize方法。其中包括PropertySourceBootstrapConfiguration#initialize 來加載外部的配置。

@Autowired(required = false)
private List<PropertySourceLocator> propertySourceLocators = new ArrayList<>();

public void initialize(ConfigurableApplicationContext applicationContext) {
	...
   for (PropertySourceLocator locator : this.propertySourceLocators) {
       //載入PropertySource
      Collection<PropertySource<?>> source = locator.locateCollection(environment);
      ...
   }
   ...
}
//org.springframework.cloud.bootstrap.config.PropertySourceLocator#locateCollection
default Collection<PropertySource<?>> locateCollection(Environment environment) {
    return locateCollection(this, environment);
}
//org.springframework.cloud.bootstrap.config.PropertySourceLocator#locateCollection
static Collection<PropertySource<?>> locateCollection(PropertySourceLocator locator, Environment environment) {
    //執行locate方法，將PropertySource加載進來
    PropertySource<?> propertySource = locator.locate(environment);
    ...
}

這個類中會注入實現了PropertySourceLocator接口的類，在nacos中是NacosPropertySourceLocator。

在initialize方法中會執行NacosPropertySourceLocator的locate方法，將NacosPropertySource加載進來。

2、NacosPropertySourceLocator的注冊

NacosPropertySourceLocator在配置類NacosConfigBootstrapConfiguration中注冊。

@Configuration(proxyBeanMethods = false)
@ConditionalOnProperty(name = "spring.cloud.nacos.config.enabled", matchIfMissing = true)
public class NacosConfigBootstrapConfiguration {

   @Bean
   @ConditionalOnMissingBean
   public NacosConfigProperties nacosConfigProperties() {
      return new NacosConfigProperties();
   }

   @Bean
   @ConditionalOnMissingBean
   public NacosConfigManager nacosConfigManager(
         NacosConfigProperties nacosConfigProperties) {
      return new NacosConfigManager(nacosConfigProperties);
   }

   @Bean
   public NacosPropertySourceLocator nacosPropertySourceLocator(
         NacosConfigManager nacosConfigManager) {
      return new NacosPropertySourceLocator(nacosConfigManager);
   }

}

在這里會依次注冊NacosConfigProperties，NacosConfigManager，NacosPropertySourceLocator。

3、加載

//com.alibaba.cloud.nacos.client.NacosPropertySourceLocator#locate
public PropertySource<?> locate(Environment env) {
   nacosConfigProperties.setEnvironment(env);
    //獲取ConfigService
   ConfigService configService = nacosConfigManager.getConfigService();

   if (null == configService) {
      log.warn("no instance of config service found, can't load config from nacos");
      return null;
   }
   long timeout = nacosConfigProperties.getTimeout();
    //構建nacosPropertySourceBuilder
   nacosPropertySourceBuilder = new NacosPropertySourceBuilder(configService,
         timeout);
   String name = nacosConfigProperties.getName();
	//獲取dataIdPrefix，一次從prefix,name,spring.application.name中獲取
   String dataIdPrefix = nacosConfigProperties.getPrefix();
   if (StringUtils.isEmpty(dataIdPrefix)) {
      dataIdPrefix = name;
   }

   if (StringUtils.isEmpty(dataIdPrefix)) {
      dataIdPrefix = env.getProperty("spring.application.name");
   }
	//構建CompositePropertySource：NACOS
   CompositePropertySource composite = new CompositePropertySource(
         NACOS_PROPERTY_SOURCE_NAME);
	//加載share 配置
   loadSharedConfiguration(composite);
   //加載extention 配置
   loadExtConfiguration(composite);
    //加載application配置
   loadApplicationConfiguration(composite, dataIdPrefix, nacosConfigProperties, env);
   return composite;
}

3.1、加載share

private void loadSharedConfiguration(
      CompositePropertySource compositePropertySource) {
   //獲取share節點的配置信息
   List<NacosConfigProperties.Config> sharedConfigs = nacosConfigProperties
         .getSharedConfigs();
    //如果不為空，加載
   if (!CollectionUtils.isEmpty(sharedConfigs)) {
      checkConfiguration(sharedConfigs, "shared-configs");
      loadNacosConfiguration(compositePropertySource, sharedConfigs);
   }
}

加載配置，公用方法

//com.alibaba.cloud.nacos.client.NacosPropertySourceLocator#loadNacosConfiguration
private void loadNacosConfiguration(final CompositePropertySource composite,
                                    List<NacosConfigProperties.Config> configs) {
    for (NacosConfigProperties.Config config : configs) {
        loadNacosDataIfPresent(composite, config.getDataId(), config.getGroup(),
                               NacosDataParserHandler.getInstance()
                               .getFileExtension(config.getDataId()),
                               config.isRefresh());
    }
}

//com.alibaba.cloud.nacos.client.NacosPropertySourceLocator#loadNacosDataIfPresent
private void loadNacosDataIfPresent(final CompositePropertySource composite,
      final String dataId, final String group, String fileExtension,
      boolean isRefreshable) {
   if (null == dataId || dataId.trim().length() < 1) {
      return;
   }
   if (null == group || group.trim().length() < 1) {
      return;
   }
    //加載NacosPropertySource，后面也會用這個方法
   NacosPropertySource propertySource = this.loadNacosPropertySource(dataId, group,
         fileExtension, isRefreshable);
    //將NacosPropertySource放入第一個
   this.addFirstPropertySource(composite, propertySource, false);
}

3.1.1、加載NacosPropertySource

//com.alibaba.cloud.nacos.client.NacosPropertySourceLocator#loadNacosPropertySource
private NacosPropertySource loadNacosPropertySource(final String dataId,
      final String group, String fileExtension, boolean isRefreshable) {
   //標注@RefreshScope的類的數量不為0，且不允許自動刷新，從緩存加載nacos的配置
    if (NacosContextRefresher.getRefreshCount() != 0) {
      if (!isRefreshable) {
         return NacosPropertySourceRepository.getNacosPropertySource(dataId,
               group);
      }
   }
   return nacosPropertySourceBuilder.build(dataId, group, fileExtension,
         isRefreshable);
}

3.1.1.1、從緩存中加載

//NacosPropertySourceRepository
private final static ConcurrentHashMap<String, NacosPropertySource> NACOS_PROPERTY_SOURCE_REPOSITORY = new ConcurrentHashMap<>();

public static NacosPropertySource getNacosPropertySource(String dataId,
      String group) {
   return NACOS_PROPERTY_SOURCE_REPOSITORY.get(getMapKey(dataId, group));
}

public static String getMapKey(String dataId, String group) {
   return String.join(NacosConfigProperties.COMMAS, String.valueOf(dataId),
         String.valueOf(group));
}

NacosPropertySourceRepository中緩存了NacosPropertySource

3.1.1.2、獲取配置并加入緩存

//com.alibaba.cloud.nacos.client.NacosPropertySourceBuilder#build
NacosPropertySource build(String dataId, String group, String fileExtension,
      boolean isRefreshable) {
    //獲取配置
   List<PropertySource<?>> propertySources = loadNacosData(dataId, group,
         fileExtension);
    //包裝成NacosPropertySource
   NacosPropertySource nacosPropertySource = new NacosPropertySource(propertySources,
         group, dataId, new Date(), isRefreshable);
    //加入緩存
   NacosPropertySourceRepository.collectNacosPropertySource(nacosPropertySource);
   return nacosPropertySource;
}

//com.alibaba.cloud.nacos.client.NacosPropertySourceBuilder#loadNacosData
private List<PropertySource<?>> loadNacosData(String dataId, String group,
      String fileExtension) {
   String data = null;
   try {
       //獲取配置
      data = configService.getConfig(dataId, group, timeout);
      if (StringUtils.isEmpty(data)) {
         log.warn(
               "Ignore the empty nacos configuration and get it based on dataId[{}] & group[{}]",
               dataId, group);
         return Collections.emptyList();
      }
      if (log.isDebugEnabled()) {
         log.debug(String.format(
               "Loading nacos data, dataId: '%s', group: '%s', data: %s", dataId,
               group, data));
      }
      return NacosDataParserHandler.getInstance().parseNacosData(dataId, data,
            fileExtension);
   }
   catch (NacosException e) {
      log.error("get data from Nacos error,dataId:{} ", dataId, e);
   }
   catch (Exception e) {
      log.error("parse data from Nacos error,dataId:{},data:{}", dataId, data, e);
   }
   return Collections.emptyList();
}

//com.alibaba.nacos.client.config.NacosConfigService#getConfig
public String getConfig(String dataId, String group, long timeoutMs) throws NacosException {
    return getConfigInner(namespace, dataId, group, timeoutMs);
}

//com.alibaba.nacos.client.config.NacosConfigService#getConfigInner
private String getConfigInner(String tenant, String dataId, String group, long timeoutMs) throws NacosException {
    group = blank2defaultGroup(group);
    ParamUtils.checkKeyParam(dataId, group);
    //聲明響應
    ConfigResponse cr = new ConfigResponse();
    //設置dataId，tenant，group
    cr.setDataId(dataId);
    cr.setTenant(tenant);
    cr.setGroup(group);
    
    // use local config first
    //先從本地緩存中加載
    String content = LocalConfigInfoProcessor.getFailover(worker.getAgentName(), dataId, group, tenant);
    if (content != null) {
        LOGGER.warn("[{}] [get-config] get failover ok, dataId={}, group={}, tenant={}, config={}",
                worker.getAgentName(), dataId, group, tenant, ContentUtils.truncateContent(content));
        cr.setContent(content);
        String encryptedDataKey = LocalEncryptedDataKeyProcessor
                .getEncryptDataKeyFailover(agent.getName(), dataId, group, tenant);
        cr.setEncryptedDataKey(encryptedDataKey);
        configFilterChainManager.doFilter(null, cr);
        content = cr.getContent();
        return content;
    }
    
    try {
        //從服務器獲取配置
        ConfigResponse response = worker.getServerConfig(dataId, group, tenant, timeoutMs, false);
        cr.setContent(response.getContent());
        cr.setEncryptedDataKey(response.getEncryptedDataKey());
        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={}",
                worker.getAgentName(), dataId, group, tenant, ioe.toString());
    }
    
    LOGGER.warn("[{}] [get-config] get snapshot ok, dataId={}, group={}, tenant={}, config={}",
            worker.getAgentName(), dataId, group, tenant, ContentUtils.truncateContent(content));
    content = LocalConfigInfoProcessor.getSnapshot(worker.getAgentName(), dataId, group, tenant);
    cr.setContent(content);
    String encryptedDataKey = LocalEncryptedDataKeyProcessor
            .getEncryptDataKeyFailover(agent.getName(), dataId, group, tenant);
    cr.setEncryptedDataKey(encryptedDataKey);
    configFilterChainManager.doFilter(null, cr);
    content = cr.getContent();
    return content;
}

3.1.2、將NacosPropertySource加入composite的第一個

//com.alibaba.cloud.nacos.client.NacosPropertySourceLocator#addFirstPropertySource
private void addFirstPropertySource(final CompositePropertySource composite,
      NacosPropertySource nacosPropertySource, boolean ignoreEmpty) {
   if (null == nacosPropertySource || null == composite) {
      return;
   }
   if (ignoreEmpty && nacosPropertySource.getSource().isEmpty()) {
      return;
   }
   composite.addFirstPropertySource(nacosPropertySource);
}

3.2、加載extention

private void loadExtConfiguration(CompositePropertySource compositePropertySource) {
    //獲取extention節點的配置信息
   List<NacosConfigProperties.Config> extConfigs = nacosConfigProperties
         .getExtensionConfigs();
    //如果不為空，加載
   if (!CollectionUtils.isEmpty(extConfigs)) {
      checkConfiguration(extConfigs, "extension-configs");
      loadNacosConfiguration(compositePropertySource, extConfigs);
   }
}

3.3、加載主配置文件

private void loadApplicationConfiguration(
      CompositePropertySource compositePropertySource, String dataIdPrefix,
      NacosConfigProperties properties, Environment environment) {
   //獲取文件擴展名
   String fileExtension = properties.getFileExtension();
    //獲取group
   String nacosGroup = properties.getGroup();
   // load directly once by default
    //加載nacos的配置
   loadNacosDataIfPresent(compositePropertySource, dataIdPrefix, nacosGroup,
         fileExtension, true);
   // load with suffix, which have a higher priority than the default
    //加載帶后綴的配置，優先級高于上一個
   loadNacosDataIfPresent(compositePropertySource,
         dataIdPrefix + DOT + fileExtension, nacosGroup, fileExtension, true);
   // Loaded with profile, which have a higher priority than the suffix
   for (String profile : environment.getActiveProfiles()) {
      String dataId = dataIdPrefix + SEP1 + profile + DOT + fileExtension;
       //加載帶profile，文件格式后綴的配置，優先級高于上一個
      loadNacosDataIfPresent(compositePropertySource, dataId, nacosGroup,
            fileExtension, true);
   }

}

這里會加載至少三個nacos上面的配置文件，按優先級依次為application,application.yaml,application-dev.yaml。