SpringCloud之RefreshScope 源碼解讀

SpringCloud之RefreshScope

@Scope 源碼解讀

• 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實現，用來實現配置、實例熱加載。

• Scope -> GenericScope -> RefreshScope
  

• Scope與ApplicationContext生命周期

  • AbstractBeanFactory#doGetBean創建Bean實例

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，並不是Scope子類。 Scope實際上是自定義擴展的接口
• Scope Bean實例交由Scope自己創建，例如SessionScope是從Session中獲取實例的，ThreadScope是從ThreadLocal中獲取的，而RefreshScope是在內建緩存中獲取的
• @Scope 對象的實例化
  • @RefreshScope 是scopeName="refresh"的 @Scope

@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Scope("refresh")
@Documented
public @interface RefreshScope {

	/**
	 * @see Scope#proxyMode()
	 * @return proxy mode
	 */
	ScopedProxyMode proxyMode() default ScopedProxyMode.TARGET_CLASS;
}

• @Scope 的注冊 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元數據， 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實例對象通過ScopedProxyFactoryBean創建，其中通過AOP使其實現ScopedObject接口，這里不再展開

@RefreshScope 源碼解讀

RefreshScope注冊

• 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

public synchronized Set<String> refresh() {
  Set<String> keys = refreshEnvironment();
  this.scope.refreshAll();
  return keys;
}

public synchronized Set<String> refreshEnvironment() {
  Map<String, Object> before = extract(
      this.context.getEnvironment().getPropertySources());
  addConfigFilesToEnvironment();
  Set<String> keys = changes(before,
      extract(this.context.getEnvironment().getPropertySources())).keySet();
  this.context.publishEvent(new EnvironmentChangeEvent(this.context, keys));
  return keys;
}

• ①提取標准參數(SYSTEM,JNDI,SERVLET)之外所有參數變量
• ②把原來的Environment里的參數放到一個新建的Spring Context容器下重新加載，完事之后關閉新容器
• ③提起更新過的參數(排除標准參數)
• ④比較出變更項
• ⑤發布環境變更事件,接收：EnvironmentChangeListener／LoggingRebinder
• ⑥RefreshScope用新的環境參數重新生成Bean
• ⑦重新生成的過程很簡單，清除refreshscope緩存幷銷毀Bean，下次就會重新從BeanFactory獲取一個新的實例（該實例使用新的配置）
• ⑧RefreshScope#refreshAll

public void refreshAll() {
        <b>super.destroy();</b>
        this.context.publishEvent(new RefreshScopeRefreshedEvent());
}

• ⑨GenericScope#destroy

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