實現Apollo配置動態刷新遇到的坑

偶遇一坑，本意為實現apollo屬性組動態映射到app內存對象，網上提供方式有2種，見https://www.cnblogs.com/linyb-geek/p/13059720.html

方案如下2種：

• 基於RefreshScope實現刷新
• 基於EnvironmentChangeEvent實現刷新

一開始，用RefreshScope，功能實現了，但是發現eureka的探針線程數量明顯增多（提升系統網絡開銷），原因是RefreshScope再刷新過程中對容器中配置bean實例，銷毀並重建導致eureka短暫抖動（eureka也是從apollo拉配置）。之后采用applicationContext.publishEvent(new EnvironmentChangeEvent(changeEvent.changedKeys()));方才避坑。

搜了一下RefreshScope的原理和機制：見https://www.cnblogs.com/javastack/p/12049139.html，發現RefreshScope實現相對比較重，使用時需要明確refresh的范圍（不建議使用refreshScope.refreshAll();）

以下轉：

@RefreshScope那些事

要說清楚RefreshScope,先要了解Scope

• Scope(org.springframework.beans.factory.config.Scope)是Spring 2.0開始就有的核心的概念

• RefreshScope(org.springframework.cloud.context.scope.refresh)是spring cloud提供的一種特殊的scope實現，用來實現配置、實例熱加載。

• Scope -> GenericScope -> RefreshScope

  
  
   

  

  scope_hierarchy.jpeg

• Scope與ApplicationContext生命周期

  • AbstractBeanFactory#doGetBean創建Bean實例

   protected <T> T doGetBean(...){ final RootBeanDefinition mbd = ... if (mbd.isSingleton()) { ... } else if (mbd.isPrototype()) ... } else { String scopeName = mbd.getScope(); final Scope scope = this.scopes.get(scopeName); Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {...}); ... } ... } 

  • Singleton和Prototype是硬編碼的，並不是Scope子類。 Scope實際上是自定義擴展的接口
  • Scope Bean實例交由Scope自己創建，例如SessionScope是從Session中獲取實例的，ThreadScope是從ThreadLocal中獲取的，而RefreshScope是在內建緩存中獲取的。

• @Scope 對象的實例化

  • @RefreshScope 是scopeName="refresh"的 @Scope

   ... @Scope("refresh") public @interface RefreshScope { ... } 

  • @Scope 的注冊 AnnotatedBeanDefinitionReader#registerBean

    public void registerBean(...){ ... ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd); abd.setScope(scopeMetadata.getScopeName()); ... definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry); } 

  • 讀取@Scope元數據， AnnotationScopeMetadataResolver#resolveScopeMetadata

  public ScopeMetadata resolveScopeMetadata(BeanDefinition definition) { AnnotationAttributes attributes = AnnotationConfigUtils.attributesFor( annDef.getMetadata(), Scope.class); if (attributes != null) { metadata.setScopeName(attributes.getString("value")); ScopedProxyMode proxyMode = attributes.getEnum("proxyMode"); if (proxyMode == null || proxyMode == ScopedProxyMode.DEFAULT) { proxyMode = this.defaultProxyMode; } metadata.setScopedProxyMode(proxyMode); } } 

  • Scope實例對象通過ScopedProxyFactoryBean創建，其中通過AOP使其實現ScopedObject接口，這里不再展開

現在來說說RefreshScope是如何實現配置和實例刷新的

• RefreshScope注冊

  • RefreshAutoConfiguration#RefreshScopeConfiguration

    @Component @ConditionalOnMissingBean(RefreshScope.class) protected static class RefreshScopeConfiguration implements BeanDefinitionRegistryPostProcessor{ ... registry.registerBeanDefinition("refreshScope", BeanDefinitionBuilder.genericBeanDefinition(RefreshScope.class) .setRole(BeanDefinition.ROLE_INFRASTRUCTURE) .getBeanDefinition()); ... } 

  • RefreshScope extends GenericScope, 大部分邏輯在 GenericScope 中
  • GenericScope#postProcessBeanFactory 中向AbstractBeanFactory注冊自己

  public class GenericScope implements Scope, BeanFactoryPostProcessor...{ @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException { beanFactory.registerScope(this.name/*refresh*/, this/*RefreshScope*/); ... } } 

• RefreshScope 刷新過程

  • 入口在ContextRefresher#refresh

   refresh() { Map<String, Object> before = ①extract( this.context.getEnvironment().getPropertySources()); ②addConfigFilesToEnvironment(); Set<String> keys = ④changes(before, ③extract(this.context.getEnvironment().getPropertySources())).keySet(); this.context.⑤publishEvent(new EnvironmentChangeEvent(keys)); this.scope.⑥refreshAll(); } 

  • ①提取標准參數(SYSTEM,JNDI,SERVLET)之外所有參數變量
  • ②把原來的Environment里的參數放到一個新建的Spring Context容器下重新加載，完事之后關閉新容器
  • ③提起更新過的參數(排除標准參數)
  • ④比較出變更項
  • ⑤發布環境變更事件,接收：EnvironmentChangeListener／LoggingRebinder
  • ⑥RefreshScope用新的環境參數重新生成Bean
  • 重新生成的過程很簡單，清除refreshscope緩存幷銷毀Bean，下次就會重新從BeanFactory獲取一個新的實例（該實例使用新的配置）
  • RefreshScope#refreshAll

    public void refreshAll() { <b>super.destroy();</b> this.context.publishEvent(new RefreshScopeRefreshedEvent()); } 

  • GenericScope#destroy

    public void destroy() { ... Collection<BeanLifecycleWrapper> wrappers = <b>this.cache.clear()</b>; for (BeanLifecycleWrapper wrapper : wrappers) { <b>wrapper.destroy();</b> } } 

• Spring Cloud Bus 如何觸發 Refresh

  • BusAutoConfiguration#BusRefreshConfiguration 發布一個RefreshBusEndpoint

  @Configuration @ConditionalOnClass({ Endpoint.class, RefreshScope.class }) protected static class BusRefreshConfiguration { @Configuration @ConditionalOnBean(ContextRefresher.class) @ConditionalOnProperty(value = "endpoints.spring.cloud.bus.refresh.enabled", matchIfMissing = true) protected static class BusRefreshEndpointConfiguration { @Bean public RefreshBusEndpoint refreshBusEndpoint(ApplicationContext context, BusProperties bus) { return new RefreshBusEndpoint(context, bus.getId()); } } } 

  • RefreshBusEndpoint 會從http端口觸發廣播RefreshRemoteApplicationEvent事件

   @Endpoint(id = "bus-refresh") public class RefreshBusEndpoint extends AbstractBusEndpoint { public void busRefresh() { publish(new RefreshRemoteApplicationEvent(this, getInstanceId(), null)); } } 

  • BusAutoConfiguration#refreshListener 負責接收事件(所有配置bus的節點)

    @Bean @ConditionalOnProperty(value = "spring.cloud.bus.refresh.enabled", matchIfMissing = true) @ConditionalOnBean(ContextRefresher.class) public RefreshListener refreshListener(ContextRefresher contextRefresher) { return new RefreshListener(contextRefresher); } 

  • RefreshListener#onApplicationEvent 觸發 ContextRefresher

  public void onApplicationEvent(RefreshRemoteApplicationEvent event) { Set<String> keys = contextRefresher.refresh(); } 

• 大部分需要更新的服務需要打上@RefreshScope, EurekaClient是如何配置更新的

  • EurekaClientAutoConfiguration#RefreshableEurekaClientConfiguration

    @Configuration @ConditionalOnRefreshScope protected static class RefreshableEurekaClientConfiguration{ @Bean @RefreshScope public EurekaClient eurekaClient(...) { return new CloudEurekaClient(manager, config, this.optionalArgs, this.context); } @Bean @RefreshScope public ApplicationInfoManager eurekaApplicationInfoManager(...) { ... return new ApplicationInfoManager(config, instanceInfo); } }