本文共 24459 字，大约阅读时间需要 81 分钟。

一、首先看一下<artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>的结构如下：

看spring.factories中内容，优先加载装配的配置

org.springframework.cloud.bootstrap.BootstrapConfiguration=\org.springframework.cloud.alibaba.nacos.NacosConfigBootstrapConfigurationorg.springframework.boot.autoconfigure.EnableAutoConfiguration=\org.springframework.cloud.alibaba.nacos.NacosConfigAutoConfiguration,\org.springframework.cloud.alibaba.nacos.endpoint.NacosConfigEndpointAutoConfigurationorg.springframework.boot.diagnostics.FailureAnalyzer=\org.springframework.cloud.alibaba.nacos.diagnostics.analyzer.NacosConnectionFailureAnalyzer

自动装配配置，进行Bean的初始化

@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);		}		NacosConfigProperties nacosConfigProperties = new NacosConfigProperties();		return nacosConfigProperties;	}	@Bean	public NacosRefreshProperties nacosRefreshProperties() {		return new NacosRefreshProperties();	}	@Bean	public NacosRefreshHistory nacosRefreshHistory() {		return new NacosRefreshHistory();	}	@Bean	public NacosContextRefresher nacosContextRefresher(			NacosConfigProperties nacosConfigProperties,			NacosRefreshProperties nacosRefreshProperties,			NacosRefreshHistory refreshHistory) {		return new NacosContextRefresher(nacosRefreshProperties, refreshHistory,				nacosConfigProperties.configServiceInstance());	}

首先远程配置的加载，spring boot 通过implements PropertySourceLocator作为入口，具体实现override locate方法

发现都调了nacosPropertySourceBuilder.build(dataId, group, fileExtension, true);

NacosPropertySourceBuilder中build通过configService.getConfig获取到远程配置。

NacosPropertySource build(String dataId, String group, String fileExtension,			boolean isRefreshable) {		Properties p = loadNacosData(dataId, group, fileExtension);		NacosPropertySource nacosPropertySource = new NacosPropertySource(group, dataId,				propertiesToMap(p), new Date(), isRefreshable);		NacosPropertySourceRepository.collectNacosPropertySources(nacosPropertySource);		return nacosPropertySource;	}	private Properties loadNacosData(String dataId, String group, String fileExtension) {		String data = null;		try {			data = configService.getConfig(dataId, group, timeout);			if (!StringUtils.isEmpty(data)) {				log.info(String.format("Loading nacos data, dataId: '%s', group: '%s'",						dataId, group));				if (fileExtension.equalsIgnoreCase("properties")) {					Properties properties = new Properties();					properties.load(new StringReader(data));					return properties;				}				else if (fileExtension.equalsIgnoreCase("yaml")						|| fileExtension.equalsIgnoreCase("yml")) {					YamlPropertiesFactoryBean yamlFactory = new YamlPropertiesFactoryBean();					yamlFactory.setResources(new ByteArrayResource(data.getBytes()));					return yamlFactory.getObject();				}			}		}		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_PROPERTIES;	}

其次是配置刷新的设计以及实现，通过NacosContextRefresher，其实现了ApplicationListener

public class NacosContextRefresher      implements ApplicationListener
   
    , ApplicationContextAware
   

当Spring上下文已经准备完毕的时候触发onApplicationEvent(ApplicationReadyEvent event)

@Override	public void onApplicationEvent(ApplicationReadyEvent event) {		// many Spring context		if (this.ready.compareAndSet(false, true)) {			this.registerNacosListenersForApplications();		}	}	@Override	public void setApplicationContext(ApplicationContext applicationContext) {		this.applicationContext = applicationContext;	}	private void registerNacosListenersForApplications() {		if (refreshProperties.isEnabled()) {			for (NacosPropertySource nacosPropertySource : NacosPropertySourceRepository					.getAll()) {				if (!nacosPropertySource.isRefreshable()) {					continue;				}				String dataId = nacosPropertySource.getDataId();				registerNacosListener(nacosPropertySource.getGroup(), dataId);			}		}	}

最后是注册了一个listener，override了receiveConfigInfo方法，

try {   configService.addListener(dataId, group, listener);}

private void registerNacosListener(final String group, final String dataId) {		Listener listener = listenerMap.computeIfAbsent(dataId, i -> new Listener() {			@Override			public void receiveConfigInfo(String configInfo) {				refreshCountIncrement();				String md5 = "";				if (!StringUtils.isEmpty(configInfo)) {					try {						MessageDigest md = MessageDigest.getInstance("MD5");						md5 = new BigInteger(1, md.digest(configInfo.getBytes("UTF-8")))								.toString(16);					}					catch (NoSuchAlgorithmException | UnsupportedEncodingException e) {						log.warn("[Nacos] unable to get md5 for dataId: " + dataId, e);					}				}				refreshHistory.add(dataId, md5);				applicationContext.publishEvent(						new RefreshEvent(this, null, "Refresh Nacos config"));				if (log.isDebugEnabled()) {					log.debug("Refresh Nacos config group " + group + ",dataId" + dataId);				}			}			@Override			public Executor getExecutor() {				return null;			}		});		try {			configService.addListener(dataId, group, listener);		}		catch (NacosException e) {			e.printStackTrace();		}	}

package主要作用：

client 启动时拉取配置信息

analyzer：FailureAnalyzer  一种很好的方式在启动时拦截异常并将其转换为易读的消息，并将其包含在FailureAnalysis中。

endpoint：主要用于暴漏SpringMvc内部运行的信息，Spring boot actuator监控端点集成

refresh:定时监听配置变化

二、接下来重点看依赖的nacos-client中的ConfigService的实现类NacosConfigService

上面提到自动装载时的代码

configService = NacosFactory.createConfigService(properties);

最后追踪到是ConfigFactory中进行了创建createConfigService，通过反射的方式创建。

public static ConfigService createConfigService(Properties properties) throws NacosException {    try {        Class
    driverImplClass = Class.forName("com.alibaba.nacos.client.config.NacosConfigService");        Constructor constructor = driverImplClass.getConstructor(Properties.class);        ConfigService vendorImpl = (ConfigService) constructor.newInstance(properties);        return vendorImpl;    } catch (Throwable e) {        throw new NacosException(-400, e.getMessage());    }}

看一下package目录：

看到NacosConfigService中有两个属性HttpAgent，ClientWorker，agent主要是http请求，worker则是负责longpolling长轮训

/**     * http agent     */    private HttpAgent agent;    /**     * longpolling     */    private ClientWorker worker;    private String namespace;    private String encode;    private ConfigFilterChainManager configFilterChainManager = new ConfigFilterChainManager();    public NacosConfigService(Properties properties) throws NacosException {        String encodeTmp = properties.getProperty(PropertyKeyConst.ENCODE);        if (StringUtils.isBlank(encodeTmp)) {            encode = Constants.ENCODE;        } else {            encode = encodeTmp.trim();        }        initNamespace(properties);        agent = new MetricsHttpAgent(new ServerHttpAgent(properties));        agent.start();        worker = new ClientWorker(agent, configFilterChainManager);    }

再看ClientWorker的构造方法，有一个固定线程池，一个cache线程池，构造方法后面固定线程池每10ms执行了checkConfigInfo()，校验cacheMap中listenerSize，如果现在listenerSize大于长轮训的数量，则全部取出进行长轮训线程池中执行长轮训，同时赋值listenerSize给长轮训数量。

public void checkConfigInfo() {        // 分任务        int listenerSize = cacheMap.get().size();        // 向上取整为批数        int longingTaskCount = (int)Math.ceil(listenerSize / ParamUtil.getPerTaskConfigSize());        if (longingTaskCount > currentLongingTaskCount) {            for (int i = (int)currentLongingTaskCount; i < longingTaskCount; i++) {                // 要判断任务是否在执行 这块需要好好想想。 任务列表现在是无序的。变化过程可能有问题                executorService.execute(new LongPollingRunnable(i));            }            currentLongingTaskCount = longingTaskCount;        }    }

public ClientWorker(final HttpAgent agent, final ConfigFilterChainManager configFilterChainManager) {    this.agent = agent;    this.configFilterChainManager = configFilterChainManager;    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.newCachedThreadPool(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() {        public void run() {            try {                checkConfigInfo();            } catch (Throwable e) {                LOGGER.error("[" + agent.getName() + "] [sub-check] rotate check error", e);            }        }    }, 1L, 10L, TimeUnit.MILLISECONDS);}

再看checkConfigInfo()，取一批新任务后，然后用上面的cache线程池执行LongPollingRunnable线程

public void checkConfigInfo() {    // 分任务    int listenerSize = cacheMap.get().size();    // 向上取整为批数    int longingTaskCount = (int)Math.ceil(listenerSize / ParamUtil.getPerTaskConfigSize());    if (longingTaskCount > currentLongingTaskCount) {        for (int i = (int)currentLongingTaskCount; i < longingTaskCount; i++) {            // 要判断任务是否在执行 这块需要好好想想。 任务列表现在是无序的。变化过程可能有问题            executorService.execute(new LongPollingRunnable(i));        }        currentLongingTaskCount = longingTaskCount;    }}

那么再看LongPollingRunnable线程run，首先是本地检测checkLocalConfig()，本地校验中可以发现本地缓存的路径是~/nacos/config/fixed-{address}_8848_nacos/snapshot/DEFAULT_GROUP/{dataId}

static {    LOCAL_FILEROOT_PATH = System.getProperty("JM.LOG.PATH", System.getProperty("user.home")) + File.separator        + "nacos" + File.separator + "config";    LOCAL_SNAPSHOT_PATH = System.getProperty("JM.SNAPSHOT.PATH", System.getProperty("user.home")) + File.separator        + "nacos" + File.separator + "config";    LOGGER.info("LOCAL_SNAPSHOT_PATH:{}", LOCAL_SNAPSHOT_PATH);}

,然后是服务器校验变化的groupKeys,通过方法checkUpdateDataIds(),之后看到cacheData.checkListenerMd5();最后的finally 中又重新通过 executorService 提交了本任务（实现长轮训，无限循环执行）。

class LongPollingRunnable implements Runnable {    private int taskId;    public LongPollingRunnable(int taskId) {        this.taskId = taskId;    }    public void run() {        try {            List
   
     cacheDatas = new ArrayList
    
     ();            // check failover config            for (CacheData cacheData : cacheMap.get().values()) {                if (cacheData.getTaskId() == taskId) {                    cacheDatas.add(cacheData);                    try {                        checkLocalConfig(cacheData);                        if (cacheData.isUseLocalConfigInfo()) {                            cacheData.checkListenerMd5();                        }                    } catch (Exception e) {                        LOGGER.error("get local config info error", e);                    }                }            }            List
     
       inInitializingCacheList = new ArrayList
      
       ();            // check server config            List
       
         changedGroupKeys = checkUpdateDataIds(cacheDatas, inInitializingCacheList);            for (String groupKey : changedGroupKeys) {                String[] key = GroupKey.parseKey(groupKey);                String dataId = key[0];                String group = key[1];                String tenant = null;                if (key.length == 3) {                    tenant = key[2];                }                try {                    String content = getServerConfig(dataId, group, tenant, 3000L);                    CacheData cache = cacheMap.get().get(GroupKey.getKeyTenant(dataId, group, tenant));                    cache.setContent(content);                    LOGGER.info("[{}] [data-received] dataId={}, group={}, tenant={}, md5={}, content={}",                        agent.getName(), dataId, group, tenant, cache.getMd5(),                        ContentUtils.truncateContent(content));                } catch (NacosException ioe) {                    String message = String.format(                        "[%s] [get-update] get changed config exception. dataId=%s, group=%s, tenant=%s",                        agent.getName(), dataId, group, tenant);                    LOGGER.error(message, ioe);                }            }            for (CacheData cacheData : cacheDatas) {                if (!cacheData.isInitializing() || inInitializingCacheList                    .contains(GroupKey.getKeyTenant(cacheData.dataId, cacheData.group, cacheData.tenant))) {                    cacheData.checkListenerMd5();                    cacheData.setInitializing(false);                }            }            inInitializingCacheList.clear();        } catch (Throwable e) {            LOGGER.error("longPolling error", e);        } finally {            executorService.execute(this);        }    }}
       
      
     
    
   

上面自动配置时，提到了最后configService.addListener(dataId, group, listener);最后是调用ClientWorker中下面的addTenantListeners方法

public void addTenantListeners(String dataId, String group, List
    listeners) {    group = null2defaultGroup(group);    String tenant = agent.getTenant();    CacheData cache = addCacheDataIfAbsent(dataId, group, tenant);    for (Listener listener : listeners) {        cache.addListener(listener);    }}

public CacheData addCacheDataIfAbsent(String dataId, String group, String tenant) {    CacheData cache = getCache(dataId, group, tenant);    if (null != cache) {        return cache;    }    String key = GroupKey.getKeyTenant(dataId, group, tenant);    cache = new CacheData(configFilterChainManager, agent.getName(), dataId, group, tenant);    synchronized (cacheMap) {        CacheData cacheFromMap = getCache(dataId, group, tenant);        // multiple listeners on the same dataid+group and race condition,so        // double check again        // other listener thread beat me to set to cacheMap        if (null != cacheFromMap) {            cache = cacheFromMap;            // reset so that server not hang this check            cache.setInitializing(true);        }        Map
   
     copy = new HashMap
    
     (cacheMap.get());        copy.put(key, cache);        cacheMap.set(copy);    }    LOGGER.info("[{}] [subscribe] {}", agent.getName(), key);    MetricsMonitor.getListenConfigCountMonitor().set(cacheMap.get().size());    return cache;}
    
   

可以看到是listener是被CacheData所持有的，下面是CacheData的主要属性，md5值在构造时getMd5String(content)，ManagerListenerWrap中有个lastCallMd5

private final String name;private final ConfigFilterChainManager configFilterChainManager;public final String dataId;public final String group;public final String tenant;private final CopyOnWriteArrayList
   
     listeners;private volatile String md5;/** * whether use local config */private volatile boolean isUseLocalConfig = false;/** * last motify time */private volatile long localConfigLastModified;private volatile String content;private int taskId;private volatile boolean isInitializing = true;
   

再看LongPollingRunnable线程run方法中CacheData的checkListenerMd5（），如果md5跟lastCallMd5不一致，则safeNotifyListener（）

void checkListenerMd5() {    for (ManagerListenerWrap wrap : listeners) {        if (!md5.equals(wrap.lastCallMd5)) {            safeNotifyListener(dataId, group, content, md5, wrap);        }    }}

safeNotifyListener是执行了listener的回调方法listener.receiveConfigInfo(contentTmp);这样上面NacosContextRefresher注册的listener就会执行receiveConfigInfo中的代码，完成了配置的更新。

private void safeNotifyListener(final String dataId, final String group, final String content,                                final String md5, final ManagerListenerWrap listenerWrap) {    final Listener listener = listenerWrap.listener;    Runnable job = new Runnable() {        public void run() {            ClassLoader myClassLoader = Thread.currentThread().getContextClassLoader();            ClassLoader appClassLoader = listener.getClass().getClassLoader();            try {                if (listener instanceof AbstractSharedListener) {                    AbstractSharedListener adapter = (AbstractSharedListener)listener;                    adapter.fillContext(dataId, group);                    LOGGER.info("[{}] [notify-context] dataId={}, group={}, md5={}", name, dataId, group, md5);                }                // 执行回调之前先将线程classloader设置为具体webapp的classloader，以免回调方法中调用spi接口是出现异常或错用（多应用部署才会有该问题）。                Thread.currentThread().setContextClassLoader(appClassLoader);                ConfigResponse cr = new ConfigResponse();                cr.setDataId(dataId);                cr.setGroup(group);                cr.setContent(content);                configFilterChainManager.doFilter(null, cr);                String contentTmp = cr.getContent();                listener.receiveConfigInfo(contentTmp);                listenerWrap.lastCallMd5 = md5;                LOGGER.info("[{}] [notify-ok] dataId={}, group={}, md5={}, listener={} ", name, dataId, group, md5,                    listener);            } catch (NacosException de) {                LOGGER.error("[{}] [notify-error] dataId={}, group={}, md5={}, listener={} errCode={} errMsg={}", name,                    dataId, group, md5, listener, de.getErrCode(), de.getErrMsg());            } catch (Throwable t) {                LOGGER.error("[{}] [notify-error] dataId={}, group={}, md5={}, listener={} tx={}", name, dataId, group,                    md5, listener, t.getCause());            } finally {                Thread.currentThread().setContextClassLoader(myClassLoader);            }        }    };    final long startNotify = System.currentTimeMillis();    try {        if (null != listener.getExecutor()) {            listener.getExecutor().execute(job);        } else {            job.run();        }    } catch (Throwable t) {        LOGGER.error("[{}] [notify-error] dataId={}, group={}, md5={}, listener={} throwable={}", name, dataId, group,            md5, listener, t.getCause());    }    final long finishNotify = System.currentTimeMillis();    LOGGER.info("[{}] [notify-listener] time cost={}ms in ClientWorker, dataId={}, group={}, md5={}, listener={} ",        name, (finishNotify - startNotify), dataId, group, md5, listener);}

上面客户端走完了闭环代码，再看客户端去服务端请求变化的配置的数据方法，设置超时时间30s

List
   
     changedGroupKeys = checkUpdateDataIds(cacheDatas, inInitializingCacheList);
   

HttpResult result = agent.httpPost(Constants.CONFIG_CONTROLLER_PATH + "/listener", headers, params,    agent.getEncode(), timeout);

请求服务端路径为/v1/cs/configs/listener，对应为nacos中的config模块中ConfigController，追踪后是调用ConfigServletInner的doPollingConfig（）

// 长轮询if (LongPollingService.isSupportLongPolling(request)) {    longPollingService.addLongPollingClient(request, response, clientMd5Map, probeRequestSize);    return HttpServletResponse.SC_OK + "";}

public void addLongPollingClient(HttpServletRequest req, HttpServletResponse rsp, Map
   
     clientMd5Map,                                 int probeRequestSize) {    String str = req.getHeader(LongPollingService.LONG_POLLING_HEADER);    String noHangUpFlag = req.getHeader(LongPollingService.LONG_POLLING_NO_HANG_UP_HEADER);    String appName = req.getHeader(RequestUtil.CLIENT_APPNAME_HEADER);    String tag = req.getHeader("Vipserver-Tag");    int delayTime = SwitchService.getSwitchInteger(SwitchService.FIXED_DELAY_TIME, 500);    /**     * 提前500ms返回响应，为避免客户端超时 @qiaoyi.dingqy 2013.10.22改动  add delay time for LoadBalance     */    long timeout = Math.max(10000, Long.parseLong(str) - delayTime);    if (isFixedPolling()) {        timeout = Math.max(10000, getFixedPollingInterval());        // do nothing but set fix polling timeout    } else {        long start = System.currentTimeMillis();        List
    
      changedGroups = MD5Util.compareMd5(req, rsp, clientMd5Map);        if (changedGroups.size() > 0) {            generateResponse(req, rsp, changedGroups);            LogUtil.clientLog.info("{}|{}|{}|{}|{}|{}|{}",                System.currentTimeMillis() - start, "instant", RequestUtil.getRemoteIp(req), "polling",                clientMd5Map.size(), probeRequestSize, changedGroups.size());            return;        } else if (noHangUpFlag != null && noHangUpFlag.equalsIgnoreCase(TRUE_STR)) {            LogUtil.clientLog.info("{}|{}|{}|{}|{}|{}|{}", System.currentTimeMillis() - start, "nohangup",                RequestUtil.getRemoteIp(req), "polling", clientMd5Map.size(), probeRequestSize,                changedGroups.size());            return;        }    }    String ip = RequestUtil.getRemoteIp(req);    // 一定要由HTTP线程调用，否则离开后容器会立即发送响应    final AsyncContext asyncContext = req.startAsync();    // AsyncContext.setTimeout()的超时时间不准，所以只能自己控制    asyncContext.setTimeout(0L);    scheduler.execute(        new ClientLongPolling(asyncContext, clientMd5Map, ip, probeRequestSize, timeout, appName, tag));}
    
   

此时交给了final ScheduledExecutorService scheduler;定时任务执行，同时定时时间为29.5秒。再看ClientLongPolling的run（）方法

@Overridepublic void run() {    asyncTimeoutFuture = scheduler.schedule(new Runnable() {        public void run() {            try {                getRetainIps().put(ClientLongPolling.this.ip, System.currentTimeMillis());                /**                 * 删除订阅关系                 */                allSubs.remove(ClientLongPolling.this);                if (isFixedPolling()) {                    LogUtil.clientLog.info("{}|{}|{}|{}|{}|{}",                        (System.currentTimeMillis() - createTime),                        "fix", RequestUtil.getRemoteIp((HttpServletRequest)asyncContext.getRequest()),                        "polling",                        clientMd5Map.size(), probeRequestSize);                    List
   
     changedGroups = MD5Util.compareMd5(                        (HttpServletRequest)asyncContext.getRequest(),                        (HttpServletResponse)asyncContext.getResponse(), clientMd5Map);                    if (changedGroups.size() > 0) {                        sendResponse(changedGroups);                    } else {                        sendResponse(null);                    }                } else {                    LogUtil.clientLog.info("{}|{}|{}|{}|{}|{}",                        (System.currentTimeMillis() - createTime),                        "timeout", RequestUtil.getRemoteIp((HttpServletRequest)asyncContext.getRequest()),                        "polling",                        clientMd5Map.size(), probeRequestSize);                    sendResponse(null);                }            } catch (Throwable t) {                LogUtil.defaultLog.error("long polling error:" + t.getMessage(), t.getCause());            }        }    }, timeoutTime, TimeUnit.MILLISECONDS);    allSubs.add(this);}
   

创建一个定时任务，同时把自己加入到allSubs中，当时间到了后，具体执行内容，把自己从allSubs移除，取消订阅关系，把变化的数据写回到reponse中

/** * 长轮询订阅关系 */final Queue
   
     allSubs;
   

但是如果服务器的配置更新后，客户端配置是如何做到实时更新配置的。查到服务器修改配置接口/v1/cs/configs，追踪代码发现有EventDispatcher.fireEvent

persistService.insertOrUpdate(srcIp, srcUser, configInfo, time, configAdvanceInfo, false);EventDispatcher.fireEvent(new ConfigDataChangeEvent(false, dataId, group, tenant, time.getTime()));

看 EventDispatcher的fireEvent

/** * fire event, notify listeners. */static public void fireEvent(Event event) {    if (null == event) {        throw new IllegalArgumentException();    }    for (AbstractEventListener listener : getEntry(event.getClass()).listeners) {        try {            listener.onEvent(event);        } catch (Exception e) {            log.error(e.toString(), e);        }    }}

它触发了AbstractEventListener的onEvent方法，那再找哪些类具体实现了AbstractEventListener的方法那？

发现了熟悉的身影LongPollingService，发现它的onEvent方法。AsyncNotifyService（用于节点之间的信息通知）

@Overridepublic void onEvent(Event event) {    if (isFixedPolling()) {        // ignore    } else {        if (event instanceof LocalDataChangeEvent) {            LocalDataChangeEvent evt = (LocalDataChangeEvent)event;            scheduler.execute(new DataChangeTask(evt.groupKey, evt.isBeta, evt.betaIps));        }    }}

再看DataChangeTask线程

线程中具体方法，遍历allSubs中的值，匹配到后，移除订阅关系，然后返回reopense,返回时首先取消等待定时执行的请求，防止写完返回值后，定时请求的再写返回值时报错。

void sendResponse(List
   
     changedGroups) {    /**     *  取消超时任务     */    if (null != asyncTimeoutFuture) {        asyncTimeoutFuture.cancel(false);    }    generateResponse(changedGroups);}
   

 

总结：nacos的config客户端采用长轮训的http请求服务器是否有配置变化。如果配置服务器变化了，则从订阅队列中取出订阅者进行实时返回的方式，来实现远程配置。

 

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