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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);
    }
}

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注解 @RefreshScope 那些事

要说清楚RefreshScope,先要了解Scope

现在来说说RefreshScope是如何实现配置和实例刷新的