Spring Cloud @RefreshScope 原理及使用

Spring Cloud @RefreshScope 原理及使用

@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与ApplicationContext生命周期

AbstractBeanFactory#doGetBean创建Bean实例

protected 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

...

}

...

}

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 before = ①extract(

this.context.getEnvironment().getPropertySources());

②addConfigFilesToEnvironment();

Set 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 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 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);

}

}

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