SpringCloud配置刷新机制的简单分析[nacos为例子]

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SpringCloud Nacos

  1. 本文主要分为SpringCloud Nacos的设计思路
  2. 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

  1. 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);
  1. com.alibaba.cloud.nacos.client.NacosPropertySourceLocator
  • 该类为nacos实现的配置发现类
  1. 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

  1. 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;
}
  1. 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

  1. 该事件为spring cloud内置的事件,用于刷新配置

com.alibaba.cloud.nacos.refresh.NacosRefreshHistory

  1. 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

  1. 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

  1. 该类是nacos用来保存拉取到的数据的
  2. 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

  1. 该类是nacos的主要刷新配置服务类
  2. 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);
  1. 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

  1. 该包提供了很多文件类型的转换器
  2. 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<String, Object> 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<String, Object> 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;
}
  1. 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

  1. 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
  1. 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<String> refresh() {
	Set<String> keys = refreshEnvironment();
	this.scope.refreshAll();
	return keys;
}

// 
public synchronized Set<String> refreshEnvironment() {
	Map<String, Object> before = extract(
			this.context.getEnvironment().getPropertySources());
	addConfigFilesToEnvironment();
	Set<String> keys = changes(before,
			extract(this.context.getEnvironment().getPropertySources())).keySet();
	this.context.publishEvent(new EnvironmentChangeEvent(this.context, keys));
	return keys;
}

  1. 该类是对RefreshEvent监听的处理
  2. 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
  1. 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,

    Java Object类 和 String类 常见问答 6k字+总结

    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());
}

  1. 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

  1. 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

最后

  1. 感谢阅读完这篇文章的大佬们,如果发现文章中有什么错误的话,请留言,不甚感激!

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