spring使用的设计模式举例说明：SpringCloud
spring使用的设计模式举例说明：SpringCloud@RefreshScope 是scopeName="refresh"的 @Scope@Scope 对象的实例化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 scop
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
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。
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); } }
作者：黄大海 https://www.jianshu.com/p/188013dd3d02
