SpringCloud配置刷新机制的简单分析[nacos为例子]
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2021-02-04 09:32
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作者 | OhOutOfMemoryError
来源 | urlify.cn/nInERf
SpringCloud Nacos
本文主要分为SpringCloud Nacos的设计思路
简单分析一下触发刷新事件后发生的过程以及一些踩坑经验
org.springframework.cloud.bootstrap.config.PropertySourceLocator
这是一个SpringCloud提供的启动器加载配置类,实现locate,注入到上下文中即可发现配置
/**
* @param environment The current Environment.
* @return A PropertySource, or null if there is none.
* @throws IllegalStateException if there is a fail-fast condition.
*/
PropertySource> locate(Environment environment);
com.alibaba.cloud.nacos.client.NacosPropertySourceLocator
该类为nacos实现的配置发现类
org.springframework.core.env.PropertySource
改类为springcloud抽象出来表达属性源的类
com.alibaba.cloud.nacos.client.NacosPropertySource / nacos实现了这个类,并赋予了其他属性
/**
* Nacos Group.
*/
private final String group;
/**
* Nacos dataID.
*/
private final String dataId;
/**
* timestamp the property get.
*/
private final Date timestamp;
/**
* Whether to support dynamic refresh for this Property Source.
*/
private final boolean isRefreshable;
大概讲解com.alibaba.cloud.nacos.client.NacosPropertySourceLocator#locate
源码解析
@Override
public PropertySource> locate(Environment env) {
nacosConfigProperties.setEnvironment(env);
// 获取nacos配置的服务类,http协议,访问nacos的api接口获得配置
ConfigService configService = nacosConfigManager.getConfigService();
if (null == configService) {
log.warn("no instance of config service found, can't load config from nacos");
return null;
}
long timeout = nacosConfigProperties.getTimeout();
// 构建一个builder
nacosPropertySourceBuilder = new NacosPropertySourceBuilder(configService,
timeout);
String name = nacosConfigProperties.getName();
String dataIdPrefix = nacosConfigProperties.getPrefix();
if (StringUtils.isEmpty(dataIdPrefix)) {
dataIdPrefix = name;
}
if (StringUtils.isEmpty(dataIdPrefix)) {
dataIdPrefix = env.getProperty("spring.application.name");
}
// 构建一个复合数据源
CompositePropertySource composite = new CompositePropertySource(
NACOS_PROPERTY_SOURCE_NAME);
// 加载共享的配置
loadSharedConfiguration(composite);
// 加载扩展配置
loadExtConfiguration(composite);
// 加载应用配置,应用配置的优先级是最高,所以这里放在最后面来做,是因为添加配置的地方都是addFirst,所以最先的反而优先级最后
loadApplicationConfiguration(composite, dataIdPrefix, nacosConfigProperties, env);
return composite;
}
每次nacos检查到配置更新的时候就会触发上下文配置刷新,就会调取locate这个方法
org.springframework.cloud.endpoint.event.RefreshEvent
该事件为spring cloud内置的事件,用于刷新配置
com.alibaba.cloud.nacos.refresh.NacosRefreshHistory
该类用于nacos刷新历史的存放,用来保存每次拉取的配置的md5值,用于比较配置是否需要刷新
com.alibaba.cloud.nacos.refresh.NacosContextRefresher
该类是Nacos用来管理一些内部监听器的,主要是配置刷新的时候可以出发回调,并且发出spring cloud上下文的配置刷新事件
com.alibaba.cloud.nacos.NacosPropertySourceRepository
该类是nacos用来保存拉取到的数据的
流程:
刷新器检查到配置更新,保存到NacosPropertySourceRepository
发起刷新事件
locate执行,直接读取NacosPropertySourceRepository
com.alibaba.nacos.client.config.NacosConfigService
该类是nacos的主要刷新配置服务类
com.alibaba.nacos.client.config.impl.ClientWorker
该类是服务类里主要的客户端,协议是HTTP
clientWorker启动的时候会初始化2个线程池,1个用于定时检查配置,1个用于辅助检查
executor = Executors.newScheduledThreadPool(1, new ThreadFactory() {
@Override
public Thread newThread(Runnable r) {
Thread t = new Thread(r);
t.setName("com.alibaba.nacos.client.Worker." + agent.getName());
t.setDaemon(true);
return t;
}
});
executorService = Executors.newScheduledThreadPool(Runtime.getRuntime().availableProcessors(), new ThreadFactory() {
@Override
public Thread newThread(Runnable r) {
Thread t = new Thread(r);
t.setName("com.alibaba.nacos.client.Worker.longPolling." + agent.getName());
t.setDaemon(true);
return t;
}
});
executor.scheduleWithFixedDelay(new Runnable() {
@Override
public void run() {
try {
checkConfigInfo();
} catch (Throwable e) {
LOGGER.error("[" + agent.getName() + "] [sub-check] rotate check error", e);
}
}
}, 1L, 10L, TimeUnit.MILLISECONDS);
com.alibaba.nacos.client.config.impl.ClientWorker.LongPollingRunnable
该类用于长轮询任务
com.alibaba.nacos.client.config.impl.CacheData#checkListenerMd5比对MD5之后开始刷新配置
com.alibaba.cloud.nacos.parser
该包提供了很多文件类型的转换器
加载数据的时候会根据文件扩展名去查找一个转换器实例
// com.alibaba.cloud.nacos.client.NacosPropertySourceBuilder#loadNacosData
private Map loadNacosData(String dataId, String group,
String fileExtension) {
String data = null;
try {
data = configService.getConfig(dataId, group, timeout);
if (StringUtils.isEmpty(data)) {
log.warn(
"Ignore the empty nacos configuration and get it based on dataId[{}] & group[{}]",
dataId, group);
return EMPTY_MAP;
}
if (log.isDebugEnabled()) {
log.debug(String.format(
"Loading nacos data, dataId: '%s', group: '%s', data: %s", dataId,
group, data));
}
Map dataMap = NacosDataParserHandler.getInstance()
.parseNacosData(data, fileExtension);
return dataMap == null ? EMPTY_MAP : dataMap;
}
catch (NacosException e) {
log.error("get data from Nacos error,dataId:{}, ", dataId, e);
}
catch (Exception e) {
log.error("parse data from Nacos error,dataId:{},data:{},", dataId, data, e);
}
return EMPTY_MAP;
}
数据会变成key value的形式,然后转换成PropertySource
如何配置一个启动配置类
由于配置上下文是属于SpringCloud管理的,所以本次的注入跟以往SpringBoot不一样
org.springframework.cloud.bootstrap.BootstrapConfiguration=\
com.alibaba.cloud.nacos.NacosConfigBootstrapConfiguration
如何在SpringCloud和SpringBoot共享一个bean呢(举个例子)
@Bean
public NacosConfigProperties nacosConfigProperties(ApplicationContext context) {
if (context.getParent() != null
&& BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
context.getParent(), NacosConfigProperties.class).length > 0) {
return BeanFactoryUtils.beanOfTypeIncludingAncestors(context.getParent(),
NacosConfigProperties.class);
}
return new NacosConfigProperties();
}
关于刷新机制的流程
org.springframework.cloud.endpoint.event.RefreshEventListener
// 外层方法
public synchronized Set refresh() {
Set keys = refreshEnvironment();
this.scope.refreshAll();
return keys;
}
//
public synchronized Set refreshEnvironment() {
Map before = extract(
this.context.getEnvironment().getPropertySources());
addConfigFilesToEnvironment();
Set keys = changes(before,
extract(this.context.getEnvironment().getPropertySources())).keySet();
this.context.publishEvent(new EnvironmentChangeEvent(this.context, keys));
return keys;
}
该类是对RefreshEvent监听的处理
直接定位到org.springframework.cloud.context.refresh.ContextRefresher#refreshEnvironment,这个方法是主要的刷新配置的方法,具体做的事:
归并得到刷新之前的配置key value
org.springframework.cloud.context.refresh.ContextRefresher#addConfigFilesToEnvironment 模拟一个新的SpringApplication,触发大部分的SpringBoot启动流程,因此也会触发读取配置,于是就会触发上文所讲的Locator,然后得到一个新的Spring应用,从中获取新的聚合配置源,与旧的Spring应用配置源进行比较,并且把本次变更的配置放置到旧的去,然后把新的Spring应用关闭
比较新旧配置,把配置拿出来,触发一个事件org.springframework.cloud.context.environment.EnvironmentChangeEvent
跳出该方法栈后,执行org.springframework.cloud.context.scope.refresh.RefreshScope#refreshAll
简单分析 EnvironmentChangeEvent
org.springframework.cloud.context.properties.ConfigurationPropertiesRebinder#rebind()
代码如下:
@ManagedOperation
public boolean rebind(String name) {
if (!this.beans.getBeanNames().contains(name)) {
return false;
}
if (this.applicationContext != null) {
try {
Object bean = this.applicationContext.getBean(name);
// 获取source对象
if (AopUtils.isAopProxy(bean)) {
bean = ProxyUtils.getTargetObject(bean);
}
if (bean != null) {
// 重新触发销毁和初始化的周期方法
this.applicationContext.getAutowireCapableBeanFactory()
.destroyBean(bean);
// 因为触发初始化生命周期,就可以触发
// org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor#postProcessBeforeInitialization
this.applicationContext.getAutowireCapableBeanFactory()
.initializeBean(bean, name);
return true;
}
}
catch (RuntimeException e) {
this.errors.put(name, e);
throw e;
}
catch (Exception e) {
this.errors.put(name, e);
throw new IllegalStateException("Cannot rebind to " + name, e);
}
}
return false;
}
该方法时接受到事件后,对一些bean进行属性重绑定,具体哪些Bean呢?
org.springframework.cloud.context.properties.ConfigurationPropertiesBeans#postProcessBeforeInitialization 该方法会在Spring refresh上下文时候执行的bean生命后期里的其中一个后置处理器,它会检查注解 @ConfigurationProperties,这些bean就是上面第一步讲的重绑定的bean
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName)
throws BeansException {
if (isRefreshScoped(beanName)) {
return bean;
}
ConfigurationProperties annotation = AnnotationUtils
.findAnnotation(bean.getClass(), ConfigurationProperties.class);
if (annotation != null) {
this.beans.put(beanName, bean);
}
else if (this.metaData != null) {
annotation = this.metaData.findFactoryAnnotation(beanName,
ConfigurationProperties.class);
if (annotation != null) {
this.beans.put(beanName, bean);
}
}
return bean;
}
简单分析org.springframework.cloud.context.scope.refresh.RefreshScope#refreshAll
@ManagedOperation(description = "Dispose of the current instance of all beans "
+ "in this scope and force a refresh on next method execution.")
public void refreshAll() {
super.destroy();
this.context.publishEvent(new RefreshScopeRefreshedEvent());
}
org.springframework.cloud.context.scope.GenericScope#destroy()
对BeanLifecycleWrapper实例集合进行销毁
BeanLifecycleWrapper是什么?
private static class BeanLifecycleWrapper {
// bean的名字
private final String name;
// 获取bean
private final ObjectFactory> objectFactory;
// 真正的实例
private Object bean;
// 销毁函数
private Runnable callback;
}
BeanLifecycleWrapper是怎么构造的?
@Override
public Object get(String name, ObjectFactory> objectFactory) {
BeanLifecycleWrapper value = this.cache.put(name,
new BeanLifecycleWrapper(name, objectFactory));
this.locks.putIfAbsent(name, new ReentrantReadWriteLock());
try {
return value.getBean();
}
catch (RuntimeException e) {
this.errors.put(name, e);
throw e;
}
}
以上代码可以追溯到Spring在创建bean的某一个分支代码,org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean 347行代码
String scopeName = mbd.getScope();
final Scope scope = this.scopes.get(scopeName);
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
}
try {
Object scopedInstance = scope.get(beanName, () -> {
beforePrototypeCreation(beanName);
try {
return createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
});
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
销毁完之后呢?其实就是把BeanLifecycleWrapper绑定的bean变成了null,那配置怎么刷新呢?@RefreshScope标记的对象一开始就是被初始化为代理对象,然后在执行它的@Value的属性的get操作的时候,会进入代理方法,代理方法里会去获取Target,这里就会触发 org.springframework.cloud.context.scope.GenericScope#get
public Object getBean() {
if (this.bean == null) {
synchronized (this.name) {
if (this.bean == null) {
// 因为bean为空,所以会触发一次bean的重新初始化,走了一遍生命周期流程所以配置又回来了
this.bean = this.objectFactory.getObject();
}
}
}
return this.bean;
}
踩坑
上面的分析简单分析到那里,那么在使用这种配置自动刷新机制有什么坑呢?
使用@RefreshScople的对象,如果把配置中心的某一行属性删掉,那么对应的bean对应的属性会变为null,但是使用@ConfigaruationProperties的对象则不会,为什么呢?因为前者是整个bean重新走了一遍生命流程,但是后者只会执行init方法
不管使用@RefreshScople和@ConfigaruationProperties都不应该在destory和init方法中执行过重的逻辑,前者会影响服务的可用性,在高并发下会阻塞太多数的请求。后者会影响配置刷新的时延性
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