一：关于Nacos的思考
首先思考一个问题，Nacos作为配置中心，Nacos 客户端是怎么实时获取到 Nacos 服务端的最新数据？
其实客户端和服务端之间的数据交互，无外乎两种情况：
1.服务端推数据给客户端
2.客户端从服务端拉数据
zk作为配置中心，基于zk的watcher机制，配置发生变化通知客户端，Nacos也是同样的原理吗？
二：Nacos的源码解析
看看Nacos是如何获取服务端的最新数据
createConfigService的作用：通过反射创建NacosConfigService
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(NacosException.CLIENT_INVALID_PARAM, e);
}
}
NacosConfigService的构造函数
new MetricsHttpAgent(new ServerHttpAgent(properties))作用：MetricsHttpAgent包装ServerHttpAgent（装饰器模式）为了做一些统计等功能。
agent.start()作用 : 监听服务器列表是否变化
public class MetricsHttpAgent implements HttpAgent {
private HttpAgent httpAgent;
public MetricsHttpAgent(HttpAgent httpAgent) {
this.httpAgent = httpAgent;
}
@Override
public void start() throws NacosException {
httpAgent.start();
}
@Override
public HttpResult httpGet(String path, List<String> headers, List<String> paramValues, String encoding, long readTimeoutMs) throws IOException {
Histogram.Timer timer = MetricsMonitor.getConfigRequestMonitor("GET", path, "NA");
HttpResult result = null;
try {
result = httpAgent.httpGet(path, headers, paramValues, encoding, readTimeoutMs);
} catch (IOException e) {
throw e;
} finally {
timer.observeDuration();
timer.close();
}
return result;
}
@Override
public HttpResult httpPost(String path, List<String> headers, List<String> paramValues, String encoding, long readTimeoutMs) throws IOException {
Histogram.Timer timer = MetricsMonitor.getConfigRequestMonitor("POST", path, "NA");
HttpResult result = null;
try {
result = httpAgent.httpPost(path, headers, paramValues, encoding, readTimeoutMs);
} catch (IOException e) {
throw e;
} finally {
timer.observeDuration();
timer.close();
}
return result;
}
@Override
public HttpResult httpDelete(String path, List<String> headers, List<String> paramValues, String encoding, long readTimeoutMs) throws IOException {
Histogram.Timer timer = MetricsMonitor.getConfigRequestMonitor("DELETE", path, "NA");
HttpResult result = null;
try {
result = httpAgent.httpDelete(path, headers, paramValues, encoding, readTimeoutMs);
} catch (IOException e) {
throw e;
} finally {
timer.observeDuration();
timer.close();
}
return result;
}
@Override
public String getName() {
return httpAgent.getName();
}
@Override
public String getNamespace() {
return httpAgent.getNamespace();
}
@Override
public String getTenant() {
return httpAgent.getTenant();
}
@Override
public String getEncode() {
return httpAgent.getEncode();
}
}
new ClientWorker(agent, configFilterChainManager, properties)的作用：线程池轮询服务器
public ClientWorker(final HttpAgent agent, final ConfigFilterChainManager configFilterChainManager, final Properties properties) {
this.agent = agent;
this.configFilterChainManager = configFilterChainManager;
// Initialize the timeout parameter
init(properties);
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);
}
checkConfigInfo作用：检查配置信息
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;
}
}
LongPollingRunnable：run方法是一个长轮询服务端过程，大致分为四块部分
第一部分：检查本地配置相关
checkLocalConfig作用：判断本地配置是否存在，是否有变更，dataId=“example”和group=“DEFAULT_GROUP”在Windows环境下默认配置路径（C:\Users\Administrator\nacos\config\fixed-localhost_8848_nacos\data\config-data\DEFAULT_GROUP\example）。
private void checkLocalConfig(CacheData cacheData) { final String dataId = cacheData.dataId; final String group = cacheData.group; final String tenant = cacheData.tenant; File path = LocalConfigInfoProcessor.getFailoverFile(agent.getName(), dataId, group, tenant); // 没有 -> 有 if (!cacheData.isUseLocalConfigInfo() && path.exists()) { String content = LocalConfigInfoProcessor.getFailover(agent.getName(), dataId, group, tenant); String md5 = MD5.getInstance().getMD5String(content); cacheData.setUseLocalConfigInfo(true); cacheData.setLocalConfigInfoVersion(path.lastModified()); cacheData.setContent(content); LOGGER.warn("[{}] [failover-change] failover file created. dataId={}, group={}, tenant={}, md5={}, content={}", agent.getName(), dataId, group, tenant, md5, ContentUtils.truncateContent(content)); return; } // 有 -> 没有。不通知业务监听器，从server拿到配置后通知。 if (cacheData.isUseLocalConfigInfo() && !path.exists()) { cacheData.setUseLocalConfigInfo(false); LOGGER.warn("[{}] [failover-change] failover file deleted. dataId={}, group={}, tenant={}", agent.getName(), dataId, group, tenant); return; } // 有变更 if (cacheData.isUseLocalConfigInfo() && path.exists() && cacheData.getLocalConfigInfoVersion() != path.lastModified()) { String content = LocalConfigInfoProcessor.getFailover(agent.getName(), dataId, group, tenant); String md5 = MD5.getInstance().getMD5String(content); cacheData.setUseLocalConfigInfo(true); cacheData.setLocalConfigInfoVersion(path.lastModified()); cacheData.setContent(content); LOGGER.warn("[{}] [failover-change] failover file changed. dataId={}, group={}, tenant={}, md5={}, content={}", agent.getName(), dataId, group, tenant, md5, ContentUtils.truncateContent(content)); } }