Spring Cloud @RefreshScope 原理及使用

更新時(shí)間：2020年01月15日 11:00:52 作者：黃大海

這篇文章主要介紹了Spring Cloud @RefreshScope 原理及使用，文中通過示例代碼介紹的非常詳細(xì)，對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值，需要的朋友們下面隨著小編來一起學(xué)習(xí)學(xué)習(xí)吧

@RefreshScope那些事

要說清楚RefreshScope,先要了解Scope

Scope(org.springframework.beans.factory.config.Scope)是Spring 2.0開始就有的核心的概念
RefreshScope(org.springframework.cloud.context.scope.refresh)是spring cloud提供的一種特殊的scope實(shí)現(xiàn)，用來實(shí)現(xiàn)配置、實(shí)例熱加載。
Scope -> GenericScope -> RefreshScope

Scope與ApplicationContext生命周期

AbstractBeanFactory#doGetBean創(chuàng)建Bean實(shí)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是硬編碼的，并不是Scope子類。 Scope實(shí)際上是自定義擴(kuò)展的接口

Scope Bean實(shí)例交由Scope自己創(chuàng)建，例如SessionScope是從Session中獲取實(shí)例的，ThreadScope是從ThreadLocal中獲取的，而RefreshScope是在內(nèi)建緩存中獲取的。

@Scope 對(duì)象的實(shí)例化

@RefreshScope 是scopeName="refresh"的 @Scope

 ...
 @Scope("refresh")
 public @interface RefreshScope {
   ...
 }

@Scope 的注冊(cè) AnnotatedBeanDefinitionReader#registerBean

 public void registerBean(...){
  ...
  ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
   abd.setScope(scopeMetadata.getScopeName());
  ...
   definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
 }

讀取@Scope元數(shù)據(jù)， 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實(shí)例對(duì)象通過ScopedProxyFactoryBean創(chuàng)建，其中通過AOP使其實(shí)現(xiàn)ScopedObject接口，這里不再展開

現(xiàn)在來說說RefreshScope是如何實(shí)現(xiàn)配置和實(shí)例刷新的

RefreshScope注冊(cè)

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, 大部分邏輯在 GenericScope 中

GenericScope#postProcessBeanFactory 中向AbstractBeanFactory注冊(cè)自己

public class GenericScope implements Scope, BeanFactoryPostProcessor...{
   @Override
   public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)
     throws BeansException {
     beanFactory.registerScope(this.name/*refresh*/, this/*RefreshScope*/);
     ...
   }
}

RefreshScope 刷新過程

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.⑥r(nóng)efreshAll();
 }

①提取標(biāo)準(zhǔn)參數(shù)(SYSTEM,JNDI,SERVLET)之外所有參數(shù)變量
②把原來的Environment里的參數(shù)放到一個(gè)新建的Spring Context容器下重新加載，完事之后關(guān)閉新容器
③提起更新過的參數(shù)(排除標(biāo)準(zhǔn)參數(shù))
④比較出變更項(xiàng)
⑤發(fā)布環(huán)境變更事件,接收：EnvironmentChangeListener／LoggingRebinder
⑥RefreshScope用新的環(huán)境參數(shù)重新生成Bean
重新生成的過程很簡(jiǎn)單，清除refreshscope緩存幷銷毀Bean，下次就會(huì)重新從BeanFactory獲取一個(gè)新的實(shí)例（該實(shí)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 如何觸發(fā) Refresh

BusAutoConfiguration#BusRefreshConfiguration 發(fā)布一個(gè)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 會(huì)從http端口觸發(fā)廣播RefreshRemoteApplicationEvent事件

 @Endpoint(id = "bus-refresh")
 public class RefreshBusEndpoint extends AbstractBusEndpoint {
    public void busRefresh() {
     publish(new RefreshRemoteApplicationEvent(this, getInstanceId(), null));
   }
 }

BusAutoConfiguration#refreshListener 負(fù)責(zé)接收事件(所有配置bus的節(jié)點(diǎn))

 @Bean
 @ConditionalOnProperty(value = "spring.cloud.bus.refresh.enabled", matchIfMissing = true)
 @ConditionalOnBean(ContextRefresher.class)
 public RefreshListener refreshListener(ContextRefresher contextRefresher) {
   return new RefreshListener(contextRefresher);
 }

RefreshListener#onApplicationEvent 觸發(fā) ContextRefresher

public void onApplicationEvent(RefreshRemoteApplicationEvent event) {
   Set<String> keys = contextRefresher.refresh();
 }

大部分需要更新的服務(wù)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);
   }
 }

以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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