@RefreshScope详解

梦里梦外; 2021-06-10 20:39 656阅读 0赞

### 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
 
 ![@RefreshScope那些事@RefreshScope那些事@RefreshScope那些事][RefreshScope_RefreshScope_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() {
 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);
 }
 }

[RefreshScope_RefreshScope_RefreshScope]: /images/20210527/b9f467a6546d4a428991b4f08e9a7d4a.png