主要分析的类

com.alibaba.csp.sentinel.dashboard.metric.MetricFetcher

在sentinel监控数据db持久化中，更换了MetricController的存储实现，可以发现com.alibaba.csp.sentinel.dashboard.repository.metric.MetricsRepository原来只有com.alibaba.csp.sentinel.dashboard.repository.metric.repository.InMemoryMetricsRepository实现

从全局可知，用到MetricsRepository的类原有的也就只有

com.alibaba.csp.sentinel.dashboard.repository.metric.repository.InMemoryMetricsRepository     监控数据的内存实现
com.alibaba.csp.sentinel.dashboard.metric.MetricFetcher    监控数据抓取器
com.alibaba.csp.sentinel.dashboard.controller.MetricController    dashboard获取监控数据入口

可以猜测监控数据获取实现的地方是在com.alibaba.csp.sentinel.dashboard.metric.MetricFetcher

还有一种方法不用猜的方式，在我们实现了dashboard的监控数据db存储后，发现

com.alibaba.csp.sentinel.dashboard.repository.metric.repository.SentinelMetricsRepository#saveAll

只要看哪里调用了存储的方法，就可以知道数据是怎么获取从而存储的。

com.alibaba.csp.sentinel.dashboard.metric.MetricFetcher#writeMetric

com.alibaba.csp.sentinel.dashboard.metric.MetricFetcher#fetchOnce

/*** fetch metric between [startTime, endTime], both side inclusive*/private void fetchOnce(String app, long startTime, long endTime, int maxWaitSeconds) {if (maxWaitSeconds <= 0) {throw new IllegalArgumentException("maxWaitSeconds must > 0, but " + maxWaitSeconds);}//获取应用的基本信息AppInfo appInfo = appManagement.getDetailApp(app);// auto remove for appif (appInfo.isDead()) {logger.info("Dead app removed: {}", app);appManagement.removeApp(app);return;}//查看应用的机器信息（比如ip）Set machines = appInfo.getMachines();logger.debug("enter fetchOnce(" + app + "), machines.size()=" + machines.size()+ ", time intervalMs [" + startTime + ", " + endTime + "]");if (machines.isEmpty()) {return;}final String msg = "fetch";AtomicLong unhealthy = new AtomicLong();final AtomicLong success = new AtomicLong();final AtomicLong fail = new AtomicLong();long start = System.currentTimeMillis();/** app_resource_timeSecond -> metric */final Map metricMap = new ConcurrentHashMap<>(16);final CountDownLatch latch = new CountDownLatch(machines.size());for (final MachineInfo machine : machines) {// 机器不正常 auto remove if (machine.isDead()) {latch.countDown();appManagement.getDetailApp(app).removeMachine(machine.getIp(), machine.getPort());logger.info("Dead machine removed: {}:{} of {}", machine.getIp(), machine.getPort(), app);continue;}if (!machine.isHealthy()) {latch.countDown();unhealthy.incrementAndGet();continue;}//机器正常的情况下final String url = "http://" + machine.getIp() + ":" + machine.getPort() + "/" + METRIC_URL_PATH+ "?startTime=" + startTime + "&endTime=" + endTime + "&refetch=" + false;final HttpGet httpGet = new HttpGet(url);httpGet.setHeader(HTTP.CONN_DIRECTIVE, HTTP.CONN_CLOSE);httpclient.execute(httpGet, new FutureCallback() {@Overridepublic void completed(final HttpResponse response) {try {handleResponse(response, machine, metricMap);success.incrementAndGet();} catch (Exception e) {logger.error(msg + " metric " + url + " error:", e);} finally {latch.countDown();}}@Overridepublic void failed(final Exception ex) {latch.countDown();fail.incrementAndGet();httpGet.abort();if (ex instanceof SocketTimeoutException) {logger.error("Failed to fetch metric from <{}>: socket timeout", url);} else if (ex instanceof ConnectException) {logger.error("Failed to fetch metric from <{}> (ConnectionException: {})", url, ex.getMessage());} else {logger.error(msg + " metric " + url + " error", ex);}}@Overridepublic void cancelled() {latch.countDown();fail.incrementAndGet();httpGet.abort();}});}try {latch.await(maxWaitSeconds, TimeUnit.SECONDS);} catch (Exception e) {logger.info(msg + " metric, wait http client error:", e);}//long cost = System.currentTimeMillis() - start;//logger.info("finished " + msg + " metric for " + app + ", time intervalMs [" + startTime + ", " + endTime//    + "], total machines=" + machines.size() + ", dead=" + dead + ", fetch success="//    + success + ", fetch fail=" + fail + ", time cost=" + cost + " ms");writeMetric(metricMap);}

final String url = "http://" + machine.getIp() + ":" + machine.getPort() + "/" + METRIC_URL_PATH+ "?startTime=" + startTime + "&endTime=" + endTime + "&refetch=" + false;final HttpGet httpGet = new HttpGet(url);

这里是调用机器的**“metric”**接口获取数据。

metric接口位于sentinel-transport【sentinel通信包】下

com.alibaba.csp.sentinel.command.handler.SendMetricCommandHandler

com.alibaba.csp.sentinel.node.metric.MetricSearcher

注释写的已经很清楚了，通过MetricSearcher查询机器的监控数据文件

com.alibaba.csp.sentinel.node.metric.MetricWriter#listMetricFiles

此方法是获取应用机器下的监控文件的。

知道了dashboard怎么获取的监控数据，那监控数据是怎么写到应用机器的磁盘？

com.alibaba.csp.sentinel.n`在这里插入代码片`ode.metric.MetricWriter#listMetricFiles

所属的类com.alibaba.csp.sentinel.node.metric.MetricWriter从命名就可以看出是写监控数据的。

com.alibaba.csp.sentinel.node.metric.MetricWriter#write

查看write方法的调用

com.alibaba.csp.sentinel.slots.block.flow.FlowRuleManager

在应用启动的时候FlowRuleManager会注册监听配置项的变化，同时也会注册MetricTimerListener，通过MetricTimerListener将监控数据写到应用所在的磁盘上，dashborad通过ip+port+方法名+参数调用获取应用磁盘上文件的监控数据。