<dependency>
            <groupId>com.ctrip.framework.apollo</groupId>
            <artifactId>apollo-client</artifactId>
            <version>2.0.1</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-config</artifactId>
            <version>2021.1</version>
        </dependency>

public class PropertySourcesProcessor implements BeanFactoryPostProcessor, EnvironmentAware,
    ApplicationEventPublisherAware, PriorityOrdered {
	// aware回調(diào)接口設(shè)置
	private ConfigurableEnvironment environment;
	@Override
  	public void setEnvironment(Environment environment) {
    	//it is safe enough to cast as all known environment is derived from ConfigurableEnvironment
    	this.environment = (ConfigurableEnvironment) environment;
  	}
	@Override
  	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
  		// 獲取配置
    	this.configUtil = ApolloInjector.getInstance(ConfigUtil.class);
    	// 從遠(yuǎn)程獲取PropertySource
    	initializePropertySources();
    	// 為每個(gè)ConfigPropertySource注冊(cè)ConfigChangeEvent監(jiān)聽器
    	// 監(jiān)聽器監(jiān)聽到ConfigChangeEvent后publish一個(gè)ApolloConfigChangeEvent
    	// 等于將apollo自定義的ConfigChangeEvent事件機(jī)制轉(zhuǎn)化為了spring的ApolloConfigChangeEvent事件
    	initializeAutoUpdatePropertiesFeature(beanFactory);
  	}
	private void initializePropertySources() {
		// 聚合類，該類也是一個(gè)PropertySource，代理了一堆PropertySource
		// 該類中有一個(gè) Set<PropertySource<?>> 字段
		CompositePropertySource composite = new ...;
		...
		// 從 遠(yuǎn)程 或 本地緩存 獲取配置
		Config config = ConfigService.getConfig(namespace);
		// 適配Config到PropertySource，并加入聚合類		
		composite.addPropertySource(configPropertySourceFactory.getConfigPropertySource(namespace, config));
		// 添加到ConfigurableEnvironment
		environment.getPropertySources().addFirst(composite);
	}
 	private void initializeAutoUpdatePropertiesFeature(ConfigurableListableBeanFactory beanFactory) {
    	if (!AUTO_UPDATE_INITIALIZED_BEAN_FACTORIES.add(beanFactory)) {
      		return;
    	}
		// 定義監(jiān)聽器，監(jiān)聽器監(jiān)聽到ConfigChangeEvent后發(fā)布ApolloConfigChangeEvent
    	ConfigChangeListener configChangeEventPublisher = changeEvent ->
        	applicationEventPublisher.publishEvent(new ApolloConfigChangeEvent(changeEvent));
		// 注冊(cè)監(jiān)聽器到每個(gè)PropertySource
    	List<ConfigPropertySource> configPropertySources = configPropertySourceFactory.getAllConfigPropertySources();
    	for (ConfigPropertySource configPropertySource : configPropertySources) {
      		configPropertySource.addChangeListener(configChangeEventPublisher);
   		}
  	}
	...
}

public class RemoteConfigRepository extends AbstractConfigRepository implements ConfigRepository{
  public RemoteConfigRepository(String namespace) {
  	...
  	// 定時(shí)拉取
	this.schedulePeriodicRefresh();
	// 長(zhǎng)輪詢
	this.scheduleLongPollingRefresh();
	...
  }
  private void schedulePeriodicRefresh() {
    // 定時(shí)線程池
    m_executorService.scheduleAtFixedRate(
        new Runnable() {
          @Override
          public void run() {
          	// 調(diào)用父抽象類trySync()
          	// trySync()調(diào)用模版方法sync()
            trySync();
          }
        }, m_configUtil.getRefreshInterval(), m_configUtil.getRefreshInterval(),
        m_configUtil.getRefreshIntervalTimeUnit());
  }
  @Override
  protected synchronized void sync() {
  	// 事務(wù)
    Transaction transaction = Tracer.newTransaction("Apollo.ConfigService", "syncRemoteConfig");
    try {
      ApolloConfig previous = m_configCache.get();
      // http遠(yuǎn)程拉取配置
      ApolloConfig current = loadApolloConfig();
      // reference equals means HTTP 304
      if (previous != current) {
        logger.debug("Remote Config refreshed!");
        // 設(shè)置緩存
        m_configCache.set(current);
        // 發(fā)布事件，該方法在父抽象類中
        this.fireRepositoryChange(m_namespace, this.getConfig());
      }

      if (current != null) {
        Tracer.logEvent(String.format("Apollo.Client.Configs.%s", current.getNamespaceName()),
            current.getReleaseKey());
      }

      transaction.setStatus(Transaction.SUCCESS);
    } catch (Throwable ex) {
      transaction.setStatus(ex);
      throw ex;
    } finally {
      transaction.complete();
    }
    ...
  }

    <dependency>
      <groupId>org.springframework.cloud</groupId>
      <artifactId>spring-cloud-context</artifactId>
      <version>...</version>
      <scope>compile</scope>
    </dependency>

public interface PropertySourceLocator {
	// 實(shí)現(xiàn)類實(shí)現(xiàn)該方法
	PropertySource<?> locate(Environment environment);
	default Collection<PropertySource<?>> locateCollection(Environment environment) {
		return locateCollection(this, environment);
	}
	static Collection<PropertySource<?>> locateCollection(PropertySourceLocator locator, Environment environment) {
		// 調(diào)用實(shí)現(xiàn)類
		PropertySource<?> propertySource = locator.locate(environment);
		if (propertySource == null) {
			return Collections.emptyList();
		}
		// 如果該P(yáng)ropertySource是代理了list的CompositePropertySource，提取全部
		if (CompositePropertySource.class.isInstance(propertySource)) {
			Collection<PropertySource<?>> sources = ((CompositePropertySource) propertySource).getPropertySources();
			List<PropertySource<?>> filteredSources = new ArrayList<>();
			for (PropertySource<?> p : sources) {
				if (p != null) {
					filteredSources.add(p);
				}
			}
			return filteredSources;
		}
		else {
			return Arrays.asList(propertySource);
		}
	}
}

@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(PropertySourceBootstrapProperties.class)
public class PropertySourceBootstrapConfiguration
		implements ApplicationContextInitializer<ConfigurableApplicationContext>, Ordered {
	@Autowired(required = false)
	private List<PropertySourceLocator> propertySourceLocators = new ArrayList<>();
	public void setPropertySourceLocators(Collection<PropertySourceLocator> propertySourceLocators) {
		this.propertySourceLocators = new ArrayList<>(propertySourceLocators);
	}
	@Override
	public void initialize(ConfigurableApplicationContext applicationContext) {
		List<PropertySource<?>> composite = new ArrayList<>();
		// 排序
		AnnotationAwareOrderComparator.sort(this.propertySourceLocators);
		boolean empty = true;
		// applicationContext由回調(diào)接口提供
		ConfigurableEnvironment environment = applicationContext.getEnvironment();
		for (PropertySourceLocator locator : this.propertySourceLocators) {
			// 調(diào)用PropertySourceLocator
			Collection<PropertySource<?>> source = locator.locateCollection(environment);
			...
			for (PropertySource<?> p : source) {
				// 是否代理了PropertySource的list做分類
				if (p instanceof EnumerablePropertySource) {
					EnumerablePropertySource<?> enumerable = (EnumerablePropertySource<?>) p;
					sourceList.add(new BootstrapPropertySource<>(enumerable));
				}
				else {
					sourceList.add(new SimpleBootstrapPropertySource(p));
				}
			}
			composite.addAll(sourceList);
			empty = false;
		}
		if (!empty) {
			// 獲取 ConfigurableEnvironment中的MutablePropertySources
			MutablePropertySources propertySources = environment.getPropertySources();
			...
			// 執(zhí)行插入到ConfigurableEnvironment的MutablePropertySources
			insertPropertySources(propertySources, composite);
			...
		}
	}
}