偶遇一坑，本意为实现apollo属性组动态映射到app内存对象，网上提供方式有2种，见https://www.cnblogs.com/linyb-geek/p/13059720.html
方案如下2种：
- 基于RefreshScope实现刷新
- 基于EnvironmentChangeEvent实现刷新
一开始，用RefreshScope，功能实现了，但是发现eureka的探针线程数量明显增多（提升系统网络开销），原因是RefreshScope再刷新过程中对容器中配置bean实例，销毁并重建导致eureka短暂抖动（eureka也是从apollo拉配置）。之后采用applicationContext.publishEvent(new EnvironmentChangeEvent(changeEvent.changedKeys()));方才避坑。
搜了一下RefreshScope的原理和机制：见https://www.cnblogs.com/javastack/p/12049139.html，发现RefreshScope实现相对比较重，使用时需要明确refresh的范围（不建议使用refreshScope.refreshAll();）
以下转：
@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_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); } }