一、查詢帶有restful api的信息，我們發(fā)現(xiàn)都是以“Resource”結(jié)尾的類

帶有api的蹤跡

首先我們先從NodeResource.java中的"/v1/node"下手，他有一個成員變量：HeartbeatFailureDetector，類中提供了所有節(jié)點的執(zhí)行狀態(tài)的封裝信息：

start
uri
recentRequests
recentFailures
recentSuccesses
lastRequestTime
lastResponseTime

 if (coordinator) {
            binder.install(new FailureDetectorModule());
            jaxrsBinder(binder).bind(NodeResource.class);
}

其中綁定了：
HeartbeatFailureDetector

HeartbeatFailureDetector這個類在PostConstruct階段(也就是類注入完成之后的階段)，開啟了定時器，每隔5s去監(jiān)聽worker的服務(wù)狀況：

@PostConstruct
    public void start()
    {
        if (isEnabled && started.compareAndSet(false, true)) {
            executor.scheduleWithFixedDelay(new Runnable()
            {
                @Override
                public void run()
                {
                    try {
                        updateMonitoredServices();
                    }
                    catch (Throwable e) {
                        // ignore to avoid getting unscheduled
                        log.warn(e, "Error updating services");
                    }
                }
            }, 0, 5, TimeUnit.SECONDS);
        }
    }

其中updateMonitoredServices使用httpclient的method為header方法去獲取信息，并把異常信息封裝起來。

 private void ping()
        {
            try {
                stats.recordStart();
                 //prepareHead為head http請求方法
                 //public static Builder prepareHead() {
                     // return new Builder().setMethod("HEAD");
                  // }
                httpClient.executeAsync(prepareHead().setUri(uri).build(), new ResponseHandler<Object, Exception>()
                {
                    @Override
                    public Exception handleException(Request request, Exception exception)
                    {
                        // ignore error
                        stats.recordFailure(exception);

                        // TODO: this will technically cause an NPE in httpClient, but it's not triggered because
                        // we never call get() on the response future. This behavior needs to be fixed in airlift
                        return null;
                    }

                    @Override
                    public Object handle(Request request, Response response)
                            throws Exception
                    {
                        stats.recordSuccess();
                        return null;
                    }
                });
            }
            catch (RuntimeException e) {
                log.warn(e, "Error scheduling request for %s", uri);
            }
        }

上面state實例記錄著狀態(tài)信息，與ServiceDescriptor（各個服務(wù)器的描述符：uuid（隨機(jī)生成）、nodeId、location等信息，從配置文件node.properties中讀取）

那，還有一個問題是，協(xié)調(diào)節(jié)點怎么獲取其他worker節(jié)點的信息的呢？

在updateMonitoredServices方法中：

 // selector.selectAllServices()獲取所有節(jié)點信息
        Set<ServiceDescriptor> online = selector.selectAllServices().stream()
                .filter(descriptor -> !nodeInfo.getNodeId().equals(descriptor.getNodeId()))
                .collect(toImmutableSet());

上面的selector是CachingServiceSelector類，此類在PostConstruct有這樣的動作：

@PostConstruct
    public void start()
    {
        if (started.compareAndSet(false, true)) {
            Preconditions.checkState(!executor.isShutdown(), "CachingServiceSelector has been destroyed");

            // if discovery is available, get the initial set of servers before starting
            try {
                refresh().get(30, TimeUnit.SECONDS);
            }
            catch (Exception ignored) {
            }
        }
    }

其中的refresh是：

 ServiceDescriptors oldDescriptors = this.serviceDescriptors.get();

        ListenableFuture<ServiceDescriptors> future;
        if (oldDescriptors == null) {
          //DiscoveryLookupClient  lookupClient
            future = lookupClient.getServices(type, pool);
        }
        else {
            future = lookupClient.refreshServices(oldDescriptors);
        }

上面的DiscoveryLookupClient是HttpDiscoveryLookupClient，看其中方法：

private ListenableFuture<ServiceDescriptors> lookup(final String type, final String pool, final ServiceDescriptors serviceDescriptors)
    {
        Preconditions.checkNotNull(type, "type is null");

        URI uri = discoveryServiceURI.get();
        if (uri == null) {
            return Futures.immediateFailedCheckedFuture(new DiscoveryException("No discovery servers are available"));
        }

        uri = URI.create(uri + "/v1/service/" + type + "/");
        if (pool != null) {
            uri = uri.resolve(pool);
        }

  Builder requestBuilder = prepareGet()
                .setUri(uri)
                .setHeader("User-Agent", nodeInfo.getNodeId());

從上面可以看出，他會去調(diào)用service api，通過get請求將nodeid做為header信息。