Spring Cloud @RefreshScope 原理是什么?

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

Scope与ApplicationContext生命周期

AbstractBeanFactory#doGetBean创建Bean实例

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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

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

@Scope 的注册 AnnotatedBeanDefinitionReader#registerBean

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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

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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

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@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

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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

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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

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

GenericScope#destroy

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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

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@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

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@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)

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@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

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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

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@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);
}

}

作者:黄大海
https://www.jianshu.com/p/188013dd3d02

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