Spring Cloud @RefreshScope 原理及使用

@RefreshScope那些事

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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