【apollo在springboot中运行原理】

系列文章目录

Springboot源码分析之apollo配置

文章目录

系列文章目录
前言
一、apollo是如何完成初始化的,拉取配置的呢
- 1. apollo的初始化阶段
- 2.初始化RemoteConfigRepository
- 3.同步远程配置
- 4.发布`ConfigFileChangeEvent`事件
总结

前言

配置中心我相信有一年开发经验的程序员都听过吧，有三年开发经验的程序100%都使用过配置中心配置吧。apollo做为常用的配置中心，你知道它的原理吗？你知道它是怎么集成到springboot的吗？
本篇文章带你了解其原理，让你也能够自定义组件。

一、apollo是如何完成初始化的,拉取配置的呢

1. apollo的初始化阶段

Springboot环境准备阶段，发布ApplicationEnvironmentPreparedEvent 事件，EnvironmentPostProcessorApplicationListener 监听到事件之后执行 postProcessEnvironment方法。apollo 中的初始化类 ApolloApplicationContextInitializer 就实现EnvironmentPostProcessor接口。
ApolloApplicationContextInitializer

  public void postProcessEnvironment(ConfigurableEnvironment configurableEnvironment, SpringApplication springApplication) {// should always initialize system properties like app.id in the first placeinitializeSystemProperty(configurableEnvironment);Boolean eagerLoadEnabled = configurableEnvironment.getProperty(PropertySourcesConstants.APOLLO_BOOTSTRAP_EAGER_LOAD_ENABLED, Boolean.class, false);//EnvironmentPostProcessor should not be triggered if you don't want Apollo Loading before Logging System Initializationif (!eagerLoadEnabled) {return;}Boolean bootstrapEnabled = configurableEnvironment.getProperty(PropertySourcesConstants.APOLLO_BOOTSTRAP_ENABLED, Boolean.class, false);if (bootstrapEnabled) {DeferredLogger.enable();//重点实现逻辑的方法initialize(configurableEnvironment);}}

2.初始化RemoteConfigRepository

经过initialize()方法层层调用最后进入到RemoteConfigRepository init

  public RemoteConfigRepository(String namespace) {m_namespace = namespace;m_configCache = new AtomicReference<>();m_configUtil = ApolloInjector.getInstance(ConfigUtil.class);m_httpClient = ApolloInjector.getInstance(HttpClient.class);m_serviceLocator = ApolloInjector.getInstance(ConfigServiceLocator.class);remoteConfigLongPollService = ApolloInjector.getInstance(RemoteConfigLongPollService.class);m_longPollServiceDto = new AtomicReference<>();m_remoteMessages = new AtomicReference<>();m_loadConfigRateLimiter = RateLimiter.create(m_configUtil.getLoadConfigQPS());m_configNeedForceRefresh = new AtomicBoolean(true);m_loadConfigFailSchedulePolicy = new ExponentialSchedulePolicy(m_configUtil.getOnErrorRetryInterval(),m_configUtil.getOnErrorRetryInterval() * 8);//下面三个方法就是拉去配置的核心代码了  //同步远程配置 this.trySync();//固定频率刷新、内部实现也是调用trySync()this.schedulePeriodicRefresh();//轮询访问远程配置中心，每次访问直到超时或者apollo 配置发生变化this.scheduleLongPollingRefresh();}

3.同步远程配置

AbstractConfigRepository.trySync()同步远程配置方法，方法内部主要实现逻辑在sync()中

protected synchronized void sync() {Transaction transaction = Tracer.newTransaction("Apollo.ConfigService", "syncRemoteConfig");try {//m_configCache ApolloConfig previous = m_configCache.get();//加载 远程 apollo configApolloConfig current = loadApolloConfig();//reference equals means HTTP 304if (previous != current) {logger.debug("Remote Config refreshed!");m_configCache.set(current);//getConfig 方法 将apollo配置放进 properties中this.fireRepositoryChange(m_namespace, this.getConfig());}if (current != null) {Tracer.logEvent(String.format("Apollo.Client.Configs.%s", current.getNamespaceName()),current.getReleaseKey());}transaction.setStatus(Transaction.SUCCESS);} catch (Throwable ex) {transaction.setStatus(ex);throw ex;} finally {transaction.complete();}}

private volatile AtomicReference<ApolloConfig> m_configCache; 使用了volatile 修饰，原子引用类型进行封装引用，这就是看源码的意义吧

4.发布`ConfigFileChangeEvent`事件

sync() 方法中的调用fireRepositoryChange(),最后会调用到AbstractConfigFile.fireConfigChange()方法

  private void fireConfigChange(final ConfigFileChangeEvent changeEvent) {for (final ConfigFileChangeListener listener : m_listeners) {m_executorService.submit(new Runnable() {@Overridepublic void run() {String listenerName = listener.getClass().getName();Transaction transaction = Tracer.newTransaction("Apollo.ConfigFileChangeListener", listenerName);try {//listner 是一个PropertySourcesProcessor 中的一个lambda 类，//ConfigChangeListener configChangeEventPublisher = changeEvent ->//applicationEventPublisher.publishEvent(new ApolloConfigChangeEvent(changeEvent));listener.onChange(changeEvent);transaction.setStatus(Transaction.SUCCESS);} catch (Throwable ex) {transaction.setStatus(ex);Tracer.logError(ex);logger.error("Failed to invoke config file change listener {}", listenerName, ex);} finally {transaction.complete();}}});}}

因此我们可以监听ApolloConfigChangeEvent事件来监听apollo配置是否发生产变化
eg：

public class ListenerApollo implements ConfigChangeListener, ApplicationListener<ApolloConfigChangeEvent> {@Overridepublic void onChange(ConfigChangeEvent configChangeEvent) {//核心线程配置发生变化、重新setConfigChange coreSize = configChangeEvent.getChange("threadPool.corePoolSize");if( coreSize!= null){ThreadPoolExecutor executor = SpringUtil.getBean(ThreadPoolExecutor.class);executor.setCorePoolSize(Integer.valueOf(coreSize.getNewValue()));}}@Overridepublic void onApplicationEvent(ApolloConfigChangeEvent event) {this.onChange(event.getConfigChangeEvent());}
}