我们经常用到apollo的两个特性：

1.动态更新配置：apollo可以动态更新@Value的值，也可以修改environment的值。

2.实时监听配置：实现apollo的监听器ConfigChangeListener，通过onChange方法来实时监听配置变化。

你知道apollo客户端是如何实现这些功能的吗？使用过程中，需要注意什么呢？

大致流程

在启动spring容器时，即会先后触发ApolloApplicationContextInitializer和ApolloConfigRegistrar为监听的namespace生成对应的config，并封装成propertySource放入env，后续更新就直接操作config，env的数据就被联动更新。

所以我们可以认为有两种方式（注解、配置）使用apollo，两者之间存在一些隐性关系（看到最后你会发现是坑哦）。

方式一：启动配置文件使用apollo——ApolloApplicationContextInitializer

com.ctrip.framework.apollo.spring.boot.ApolloApplicationContextInitializer#initialize(org.springframework.context.ConfigurableApplicationContext)

publicvoidinitialize(ConfigurableApplicationContext context){ConfigurableEnvironment environment = context.getEnvironment();

	//必须开启apollo.bootstrap.enabledString enabled = environment.getProperty(PropertySourcesConstants.APOLLO_BOOTSTRAP_ENABLED,"false");if(!Boolean.valueOf(enabled)){
      logger.debug("Apollo bootstrap config is not enabled for context {}, see property: ${
    {}}", context,PropertySourcesConstants.APOLLO_BOOTSTRAP_ENABLED);return;}
    logger.debug("Apollo bootstrap config is enabled for context {}", context);//！！！生成config,刷新器，将config塞入environment配置列表最前面（顺序决定优先级）initialize(environment);}protectedvoidinitialize(ConfigurableEnvironment environment){if(environment.getPropertySources().contains(PropertySourcesConstants.APOLLO_BOOTSTRAP_PROPERTY_SOURCE_NAME)){//already initializedreturn;}
	//从apollo.bootstrap.namespaces获取namespace，默认还是applicationString namespaces = environment.getProperty(PropertySourcesConstants.APOLLO_BOOTSTRAP_NAMESPACES,ConfigConsts.NAMESPACE_APPLICATION);
    logger.debug("Apollo bootstrap namespaces: {}", namespaces);List<String> namespaceList =NAMESPACE_SPLITTER.splitToList(namespaces);

	//生成名为ApolloBootstrapPropertySources的CompositePropertySource ，所有namespace共用该propertysource，namespace的顺序也是优先级顺序CompositePropertySource composite =newCompositePropertySource(PropertySourcesConstants.APOLLO_BOOTSTRAP_PROPERTY_SOURCE_NAME);for(String namespace : namespaceList){
    	//生成config（该部分公用，后续分析）Config config =ConfigService.getConfig(namespace);//封装为propertsource
     composite.addPropertySource(configPropertySourceFactory.getConfigPropertySource(namespace, config));}//最后添加到environment中，这里决定了优先级比注解高
    environment.getPropertySources().addFirst(composite);}

开启配置方式（apollo.bootstrap.enabled为true），则会触发ApolloAutoConfiguration 创建对应的处理器监听器，如动态修改@Value数据

@Configuration@ConditionalOnProperty(PropertySourcesConstants.APOLLO_BOOTSTRAP_ENABLED)@ConditionalOnMissingBean(PropertySourcesProcessor.class)publicclassApolloAutoConfiguration{@BeanpublicConfigPropertySourcesProcessorconfigPropertySourcesProcessor(){returnnewConfigPropertySourcesProcessor();}}publicclassConfigPropertySourcesProcessorextendsPropertySourcesProcessorimplementsBeanDefinitionRegistryPostProcessor{@OverridepublicvoidpostProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry)throwsBeansException{Map<String,Object> propertySourcesPlaceholderPropertyValues =newHashMap<>();// to make sure the default PropertySourcesPlaceholderConfigurer's priority is higher than PropertyPlaceholderConfigurer
    propertySourcesPlaceholderPropertyValues.put("order",0);BeanRegistrationUtil.registerBeanDefinitionIfNotExists(registry,PropertySourcesPlaceholderConfigurer.class.getName(),PropertySourcesPlaceholderConfigurer.class, propertySourcesPlaceholderPropertyValues);BeanRegistrationUtil.registerBeanDefinitionIfNotExists(registry,ApolloAnnotationProcessor.class.getName(),ApolloAnnotationProcessor.class);BeanRegistrationUtil.registerBeanDefinitionIfNotExists(registry,SpringValueProcessor.class.getName(),SpringValueProcessor.class);BeanRegistrationUtil.registerBeanDefinitionIfNotExists(registry,ApolloJsonValueProcessor.class.getName(),ApolloJsonValueProcessor.class);processSpringValueDefinition(registry);}/**
   * For Spring 3.x versions, the BeanDefinitionRegistryPostProcessor would not be
   * instantiated if it is added in postProcessBeanDefinitionRegistry phase, so we have to manually
   * call the postProcessBeanDefinitionRegistry method of SpringValueDefinitionProcessor here...
   */privatevoidprocessSpringValueDefinition(BeanDefinitionRegistry registry){SpringValueDefinitionProcessor springValueDefinitionProcessor =newSpringValueDefinitionProcessor();

    springValueDefinitionProcessor.postProcessBeanDefinitionRegistry(registry);}}

方式二：使用注解@EnableApolloConfig开启apollo

通过导入ApolloConfigRegistrar，触发PropertySourcesProcessor。

【创建application的beandefinition以后】

publicvoidregisterBeanDefinitions(AnnotationMetadata importingClassMetadata,BeanDefinitionRegistry registry){AnnotationAttributes attributes =AnnotationAttributes.fromMap(importingClassMetadata
        .getAnnotationAttributes(EnableApolloConfig.class.getName()));//从注解@EnableApolloConfig的value获取namespaceString[] namespaces = attributes.getStringArray("value");int order = attributes.getNumber("order");//在PropertySourcesProcessor添加namespace,order信息PropertySourcesProcessor.addNamespaces(Lists.newArrayList(namespaces), order);Map<String,Object> propertySourcesPlaceholderPropertyValues =newHashMap<>();// to make sure the default PropertySourcesPlaceholderConfigurer's priority is higher than PropertyPlaceholderConfigurer
    propertySourcesPlaceholderPropertyValues.put("order",0);BeanRegistrationUtil.registerBeanDefinitionIfNotExists(registry,PropertySourcesPlaceholderConfigurer.class.getName(),PropertySourcesPlaceholderConfigurer.class, propertySourcesPlaceholderPropertyValues);
	//创建PropertySourcesProcessor为namespace生成config等BeanRegistrationUtil.registerBeanDefinitionIfNotExists(registry,PropertySourcesProcessor.class.getName(),PropertySourcesProcessor.class);BeanRegistrationUtil.registerBeanDefinitionIfNotExists(registry,ApolloAnnotationProcessor.class.getName(),ApolloAnnotationProcessor.class);BeanRegistrationUtil.registerBeanDefinitionIfNotExists(registry,SpringValueProcessor.class.getName(),SpringValueProcessor.class);BeanRegistrationUtil.registerBeanDefinitionIfNotExists(registry,SpringValueDefinitionProcessor.class.getName(),SpringValueDefinitionProcessor.class);BeanRegistrationUtil.registerBeanDefinitionIfNotExists(registry,ApolloJsonValueProcessor.class.getName(),ApolloJsonValueProcessor.class);}

PropertySourcesProcessor初始化config（namespace排序），自动更新spring @Value的值

【在创建完所有beandefinition后触发】

publicvoidpostProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)throwsBeansException{
	//1.初始化config,刷新器，关联environmentinitializePropertySources();//2.初始化AutoUpdateConfigChangeListener，自动更新spring @Value的值initializeAutoUpdatePropertiesFeature(beanFactory);}privatevoidinitializePropertySources(){if(environment.getPropertySources().contains(PropertySourcesConstants.APOLLO_PROPERTY_SOURCE_NAME)){//already initializedreturn;}//生成名为ApolloPropertySources的CompositePropertySource ，所有namespace共用该propertysourceCompositePropertySource composite =newCompositePropertySource(PropertySourcesConstants.APOLLO_PROPERTY_SOURCE_NAME);//排序ImmutableSortedSet<Integer> orders =ImmutableSortedSet.copyOf(NAMESPACE_NAMES.keySet());Iterator<Integer> iterator = orders.iterator();while(iterator.hasNext()){int order = iterator.next();//按照order为每个namespace创建config(公用部分，后续分析）for(String namespace :NAMESPACE_NAMES.get(order)){Config config =ConfigService.getConfig(namespace);
        composite.addPropertySource(configPropertySourceFactory.getConfigPropertySource(namespace, config));}}// clean upNAMESPACE_NAMES.clear();// 在environment的ApolloBootstrapPropertySources后面或者直接在第一个位置加上前面封装的compsite propertysource，保证注解优先级低于配置方式if(environment.getPropertySources().contains(PropertySourcesConstants.APOLLO_BOOTSTRAP_PROPERTY_SOURCE_NAME)){// ensure ApolloBootstrapPropertySources is still the firstensureBootstrapPropertyPrecedence(environment);

      environment.getPropertySources().addAfter(PropertySourcesConstants.APOLLO_BOOTSTRAP_PROPERTY_SOURCE_NAME, composite);}else{
      environment.getPropertySources().addFirst(composite);}}

创建Config的系列操作

触发创建RemoteConfigRepository（内部包含首次同步apollo，启动定时刷新器，长轮训刷新器）

创建RemoteConfigRepository

之前说的 ConfigService.getConfig(namespace) ，获取不到config，就会创建一个config，最终创建RemoteConfigRepository。看其构造方法，除了各种属性赋值后，还会调用三个方法，它们很关键哈。

public RemoteConfigRepository(String namespace) {
  m_namespace = namespace;
  m_configCache = new AtomicReference<>();
  m_configUtil = ApolloInjector.getInstance(ConfigUtil.class);
  m_httpUtil = ApolloInjector.getInstance(HttpUtil.class);
  m_serviceLocator = ApolloInjector.getInstance(ConfigServiceLocator.class);
  remoteConfigLongPollService = ApolloInjector.getInstance(RemoteConfigLongPollService.class);
  m_longPollServiceDto = new AtomicReference<>();
  m_remoteMessages = new AtomicReference<>();
  m_loadConfigRateLimiter = RateLimiter.create(m_configUtil.getLoadConfigQPS());
  m_configNeedForceRefresh = new AtomicBoolean(true);
  m_loadConfigFailSchedulePolicy = new ExponentialSchedulePolicy(m_configUtil.getOnErrorRetryInterval(),
      m_configUtil.getOnErrorRetryInterval() * 8);
  gson = new Gson();
  // 首次同步apollo
  this.trySync();
  // 定时刷新配置（大部分情况返回304，定时刷新在于可以防止长轮询失败）
  this.schedulePeriodicRefresh();
  // 长轮询刷新配置（最主要的实时获取配置的途径）
  this.scheduleLongPollingRefresh();
}

首次同步apollo

@Override
protected synchronized void sync() {
  Transaction transaction = Tracer.newTransaction("Apollo.ConfigService", "syncRemoteConfig");

  try {
    ApolloConfig previous = m_configCache.get();
    // 根据你设定的apollo地址，appId，maxRetries等信息，发送get请求，获取当前apollo配置信息
    ApolloConfig current = loadApolloConfig();

    // 更新本地的apollo配置信息
    if (previous != current) {
      logger.debug("Remote Config refreshed!");
      m_configCache.set(current);
      // 刷新配置的任务可能会调用该方法，获取配置，并且通知客户端的监听器
      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();
  }
}

开启定时刷新配置

private void schedulePeriodicRefresh() {
  logger.debug("Schedule periodic refresh with interval: {} {}",
      m_configUtil.getRefreshInterval(), m_configUtil.getRefreshIntervalTimeUnit());
  m_executorService.scheduleAtFixedRate(
      new Runnable() {
        @Override
        public void run() {
          Tracer.logEvent("Apollo.ConfigService", String.format("periodicRefresh: %s", m_namespace));
          logger.debug("refresh config for namespace: {}", m_namespace);
          // 和上述首次同步的trySync是同一个方法
          trySync();
          Tracer.logEvent("Apollo.Client.Version", Apollo.VERSION);
        }
          //时间间隔默认是5分钟
      }, m_configUtil.getRefreshInterval(), m_configUtil.getRefreshInterval(),
      m_configUtil.getRefreshIntervalTimeUnit());
}

开启长轮询刷新配置

public boolean submit(String namespace, RemoteConfigRepository remoteConfigRepository) {
  boolean added = m_longPollNamespaces.put(namespace, remoteConfigRepository);
  m_notifications.putIfAbsent(namespace, INIT_NOTIFICATION_ID);
  if (!m_longPollStarted.get()) {
    // 开启拉取  
    startLongPolling();
  }
  return added;
}

private void doLongPollingRefresh(String appId, String cluster, String dataCenter) {
  final Random random = new Random();
  ServiceDTO lastServiceDto = null;
  while (!m_longPollingStopped.get() && !Thread.currentThread().isInterrupted()) {
    if (!m_longPollRateLimiter.tryAcquire(5, TimeUnit.SECONDS)) {
      // 等待5秒
      try {
        TimeUnit.SECONDS.sleep(5);
      } catch (InterruptedException e) {
      }
    }
      
      // 获取各种信息，发起请求，看apollo中配置有无变更
      ......
          
      //200说明 配置发生变化，则主动获取新配置，且调用ConfigChangeListener的实现类的onChange方法    
      if (response.getStatusCode() == 200 && response.getBody() != null) {
        updateNotifications(response.getBody());
        updateRemoteNotifications(response.getBody());
        transaction.addData("Result", response.getBody().toString());
        notify(lastServiceDto, response.getBody());
      }
       
    //需要重新长链接
    //长链接可以监听服务端动态，不需要频繁与服务器建连访问，可以降低资源消耗，也可以得到及时变更通知
    if (response.getStatusCode() == 304 && random.nextBoolean()) {
      lastServiceDto = null;
    }

       ......
    } finally {
      transaction.complete();
    }
  }
}

notify方法会最终进入fireRepositoryChange

sync->fireRepositoryChange

该方法是之前介绍的sync()方法里面提到的，两类刷新配置的任务都会执行此方法，来通知各个监听器，有哪些配置变更。

1.获取新配置

2.统计各种配置的变更

3.通知各个监听器

protected void fireRepositoryChange(String namespace, Properties newProperties) {
  // 遍历所有的监听器
  for (RepositoryChangeListener listener : m_listeners) {
    try {
      // 把最新的配置信息传递给监听器
      listener.onRepositoryChange(namespace, newProperties);
    } catch (Throwable ex) {
      Tracer.logError(ex);
      logger.error("Failed to invoke repository change listener {}", listener.getClass(), ex);
    }
  }
}

@Override
public synchronized void onRepositoryChange(String namespace, Properties newProperties) {
  if (newProperties.equals(m_configProperties.get())) {
    return;
  }

  ConfigSourceType sourceType = m_configRepository.getSourceType();
  Properties newConfigProperties = new Properties();
  newConfigProperties.putAll(newProperties);

  // 整理且更新配置信息，确定配置的变更类型
  Map<String, ConfigChange> actualChanges = updateAndCalcConfigChanges(newConfigProperties, sourceType);

  //check double checked result
  if (actualChanges.isEmpty()) {
    return;
  }

  // 调用各个ConfigChangeListener实现类的onChange方法，发送配置信息
  this.fireConfigChange(new ConfigChangeEvent(m_namespace, actualChanges));

  Tracer.logEvent("Apollo.Client.ConfigChanges", m_namespace);
}

private Map<String, ConfigChange> updateAndCalcConfigChanges(Properties newConfigProperties,
    ConfigSourceType sourceType) {
  // 初次统计变化的配置  
  List<ConfigChange> configChanges =
      calcPropertyChanges(m_namespace, m_configProperties.get(), newConfigProperties);

  ImmutableMap.Builder<String, ConfigChange> actualChanges =
      new ImmutableMap.Builder<>();

  /** === Double check since DefaultConfig has multiple config sources ==== **/

  //1. 为配置设置旧值
  for (ConfigChange change : configChanges) {
    change.setOldValue(this.getProperty(change.getPropertyName(), change.getOldValue()));
  }

  //2. 更新 m_configProperties，该处本地env配置被更新
  updateConfig(newConfigProperties, sourceType);
  clearConfigCache();

  //3. 遍历所有的新配置，最后确认各个配置的type（ADDED/MODIFIED/DELETED）
  for (ConfigChange change : configChanges) {
    change.setNewValue(this.getProperty(change.getPropertyName(), change.getNewValue()));
    switch (change.getChangeType()) {
      case ADDED:
        if (Objects.equals(change.getOldValue(), change.getNewValue())) {
          break;
        }
        if (change.getOldValue() != null) {
          change.setChangeType(PropertyChangeType.MODIFIED);
        }
        actualChanges.put(change.getPropertyName(), change);
        break;
      case MODIFIED:
        if (!Objects.equals(change.getOldValue(), change.getNewValue())) {
          actualChanges.put(change.getPropertyName(), change);
        }
        break;
      case DELETED:
        if (Objects.equals(change.getOldValue(), change.getNewValue())) {
          break;
        }
        if (change.getNewValue() != null) {
          change.setChangeType(PropertyChangeType.MODIFIED);
        }
        actualChanges.put(change.getPropertyName(), change);
        break;
      default:
        //do nothing
        break;
    }
  }
  return actualChanges.build();
}

总结两种方式的异同

相同之处：

1.创建config的流程和最终关联environment的方式。

2.默认情况下，都是使用application namespace。

不同之处：

1.注解模式优先级低于配置方式。

2. 注解可以在多个地方使用，可以批量设置注解的namespace的优先级；配置文件只能按照配置的顺序来决定优先级。

可能存在的坑

1.如果配置方式和注解方式同时使用，则优先从配置方式里面的namespace读取配置，没有则会从注解的namespace读取配置，不要误以为只会用配置文件指定的namespace！！！

2.如果只是监听application 这个namespace，可以使用ConfigService.getAppConfig()，如果是监听其他XXX namespace，一定要用ConfigService.getAppConfig(“XXX”)，不然，就会因为你是用的api触发监听application！！！也就是，即便你只用了配置方式，明确了使用XXXnamespace，还是会以application作为兜底！！！