Spring Cloud @RefreshScope 原理是什么？

以你之姓@ 2022-11-05 08:51 253阅读 0赞

要清楚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

![0f69edbd732f7d0a70a7c242c1fa096f.png][]

**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。

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() {
 super.destroy();
 this.context.publishEvent(new RefreshScopeRefreshedEvent());
 }

GenericScope\#destroy

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

**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);
      }
      
    }

> [https://www.cnblogs.com/javastack/p/12049139.html][https_www.cnblogs.com_javastack_p_12049139.html]

[0f69edbd732f7d0a70a7c242c1fa096f.png]: /images/20221023/8ba18c751a7e4a2b9292394cadc69e2a.png
[https_www.cnblogs.com_javastack_p_12049139.html]: https://www.cnblogs.com/javastack/p/12049139.html