@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，并不是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提取標準參數(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(排除標準參數)
  • 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);
        }
    }