@RefreshScope详解

要说清楚RefreshScope,先要了解Scope

• Scope(org.springframework.beans.factory.config.Scope)是Spring 2.0开始就有的核心的概念
• RefreshScope(org.springframework.cloud.context.scope.refresh)是spring cloud提供的一种特殊的scope实现，用来实现配置、实例热加载。
• Scope -> GenericScope -> RefreshScope

  

  scope_hierarchy.jpeg

• Scope与ApplicationContext生命周期
  • AbstractBeanFactory#doGetBean创建Bean实例

   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是硬编码的，并不是Scope子类。 Scope实际上是自定义扩展的接口
  • Scope Bean实例交由Scope自己创建，例如SessionScope是从Session中获取实例的，ThreadScope是从ThreadLocal中获取的，而RefreshScope是在内建缓存中获取的。

• @Scope 对象的实例化
  • @RefreshScope 是scopeName=”refresh”的 @Scope

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

  • @Scope 的注册 AnnotatedBeanDefinitionReader#registerBean

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

  • 读取@Scope元数据， 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实例对象通过ScopedProxyFactoryBean创建，其中通过AOP使其实现ScopedObject接口，这里不再展开

现在来说说RefreshScope是如何实现配置和实例刷新的

• RefreshScope注册
  • 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, 大部分逻辑在 GenericScope 中
  • GenericScope#postProcessBeanFactory 中向AbstractBeanFactory注册自己

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

• RefreshScope 刷新过程
  • 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提取标准参数(SYSTEM,JNDI,SERVLET)之外所有参数变量
  • ②把原来的Environment里的参数放到一个新建的Spring Context容器下重新加载，完事之后关闭新容器
  • ③提起更新过的参数(排除标准参数)
  • ④比较出变更项
  • ⑤发布环境变更事件,接收：EnvironmentChangeListener／LoggingRebinder
  • ⑥RefreshScope用新的环境参数重新生成Bean
  • 重新生成的过程很简单，清除refreshscope缓存幷销毁Bean，下次就会重新从BeanFactory获取一个新的实例（该实例使用新的配置）
  • 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 如何触发 Refresh
  • BusAutoConfiguration#BusRefreshConfiguration 发布一个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 会从http端口触发广播RefreshRemoteApplicationEvent事件

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

  • BusAutoConfiguration#refreshListener 负责接收事件(所有配置bus的节点)

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

  • RefreshListener#onApplicationEvent 触发 ContextRefresher

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

• 大部分需要更新的服务需要打上@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);
        }
    }