获取大致流程

客户端获取服务

前面讲了服务注册，续约，现在还有个获取服务，也是初始化的时候开启的调度任务CacheRefreshThread：

DiscoveryClient的refreshRegistry刷新注册表

核心方法就是fetchRegistry。

    void refreshRegistry() {
            try {
                boolean remoteRegionsModified = false;
               	...
                boolean success = fetchRegistry(remoteRegionsModified);
    			..
             
            } catch (Throwable e) {
                logger.error("Cannot fetch registry from server", e);
            }
        }

fetchRegistry

主要思想就是先判断是增量拉去还是全量拉去，一般一开始就全量拉去，后面是增量，毕竟增量效率高啊。最后获取完信息后比对一下AppsHashCode，也就是比对数据的完整性，保证拉去的信息和注册中心的是一致的。

      private boolean fetchRegistry(boolean forceFullRegistryFetch) {
    		...
            try {
                // If the delta is disabled or if it is the first time, get all
                // applications
                Applications applications = getApplications();//获取已在本地的服务
    
                if (clientConfig.shouldDisableDelta()//配置禁止增量
                        || (!Strings.isNullOrEmpty(clientConfig.getRegistryRefreshSingleVipAddress()))
                        || forceFullRegistryFetch//强制
                        || (applications == null)//没有服务信息
                        || (applications.getRegisteredApplications().size() == 0)//没有服务信息
                        || (applications.getVersion() == -1)) //Client application does not have latest library supporting delta
                {
                	...
                    getAndStoreFullRegistry();
                } else {
                    getAndUpdateDelta(applications);
                }
                applications.setAppsHashCode(applications.getReconcileHashCode());
                logTotalInstances();
            } catch (Throwable e) {
                logger.error(PREFIX + "{} - was unable to refresh its cache! status = {}", appPathIdentifier, e.getMessage(), e);
                return false;
            } finally {
              	...
            }
    		...
            return true;
        }

getAndStoreFullRegistry全量获取

主要还是调用jersey的，最终到AbstractJerseyEurekaHttpClient的getApplicationsInternal，获取后方本地缓存localRegionApps。

最后是这里：

getAndUpdateDelta增量获取

其实就是调用jersey的增量获取接口，获取增量后判断，如果是null的话说明有问题，就进行一次全量获取，如果有增量，就进行更新，并比对数据一致性的AppsHashCode，如果有问题就进行全量获取reconcileAndLogDifference。

    private void getAndUpdateDelta(Applications applications) throws Throwable {
            long currentUpdateGeneration = fetchRegistryGeneration.get();
    		//增量
            Applications delta = null;
            EurekaHttpResponse<Applications> httpResponse = eurekaTransport.queryClient.getDelta(remoteRegionsRef.get());
            if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
                delta = httpResponse.getEntity();
            }
    
            if (delta == null) {
    			//如果增量为null，就进行一次全量
                getAndStoreFullRegistry();
            } else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
    
                String reconcileHashCode = "";
                if (fetchRegistryUpdateLock.tryLock()) {
                    try {
                        updateDelta(delta);//更新增量
                        reconcileHashCode = getReconcileHashCode(applications);//获取数据一致的AppsHashCode
                    } finally {
                        fetchRegistryUpdateLock.unlock();
                    }
                } else {
                    
                }
                // There is a diff in number of instances for some reason
                if (!reconcileHashCode.equals(delta.getAppsHashCode()) || clientConfig.shouldLogDeltaDiff()) {//比对AppsHashCode，如果不一致说明有问题，进行一次全量获取
                    reconcileAndLogDifference(delta, reconcileHashCode);  // this makes a remoteCall
                }
            } else {
    
            }
        }

细节下篇说吧。

好了，今天就到这里了，希望对学习理解有帮助，大神看见勿喷，仅为自己的学习理解，能力有限，请多包涵。

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